Convert the electronic transformer into a more powerful one. Increasing the power of the electronic transformer
The electronic transformer is a network switching power supply with very good performance. Such power supplies do not have short circuit protection at the output, but this defect can be corrected. Today I decided to present the entire process of increasing the power of electronic transformers for halogen lamps. We will turn a Chinese electric power supply with a power of 150 watts into a powerful UPS that can be used for almost any purpose. The secondary winding of the pulse transformer, in my case, contains only one turn. The winding is wound with 10 strands of 0.5 mm wire. The power supply is capable of up to 300 watts, therefore, it can be used for low frequencies such as Holton, Lanzar, Marshall Leach, etc. If desired, you can assemble a powerful laboratory power supply based on such a UPS. We know that many UPSs of this type do not turn on without load; Tashibra electronic transformers with a power of 105 watts have this drawback.
Our circuit does not have such a drawback; the circuit starts without load and can work with low-power loads (LEDs, etc.). To make it more powerful, you need to make a few modifications. You need to rewind the pulse transformer, select half-bridge capacitors, replace the diodes in the rectifier and use more powerful switches. In my case, I used one and a half ampere diodes, which I did not replace, but be sure to replace them with any diodes with a reverse voltage of at least 400 Volts and a current of 2 Amps or more.
First, let's remake the pulse transformer. On the board you can see a ring transformer with two windings; both windings need to be removed. Then we take another similar ring (removed from the same block) and glue them together. The network winding consists of 90 turns, the turns are stretched across the entire ring.
The diameter of the wire with which the winding is wound is 0.5...0.7 mm. Next we wind the secondary winding. One turn gives one and a half volts, for example - to obtain 12 volts of output voltage, the winding must contain 8 turns (but there are other values).
Next, we replace the half-bridge capacitors. The standard circuit uses 0.22 µF 630 Volt capacitors, which were replaced with 0.5 µF 400 Volt capacitors. Power switches were used in the MJE13007 series, which were replaced with more powerful ones - MJE13009.
At this point, the conversion is almost complete and you can already connect it to a 220 Volt network. After checking the functionality of the circuit, we move on. We supplement the mains voltage UPS. The filter contains chokes and a smoothing capacitor. The electrolytic capacitor is selected with a calculation of 1 µF per 1 Volt; for our 300 Watts we select a capacitor with a capacity of 300 µF with a minimum voltage of 400 Volts. Next we move on to the throttles. I used a ready-made choke, it was unsoldered from another UPS. The inductor has two separate windings of 30 turns of 0.4 mm wire.
You can put a fuse at the power input, but in my case it was already on the board. The fuse is selected for 1.25 - 1.5 Ampere. Now everything is ready, you can already supplement the circuit with an output rectifier and smoothing filters. If you plan to assemble a charger for a car battery based on such a UPS, then one powerful Schottky diode will be enough at the output. These diodes include the powerful pulse diode STPR40 series, which is often used in computer power supplies. The current of the specified diode is 20 Amperes, but for a 300 watt power supply and 20 Amps is not enough. No problem! The fact is that the indicated diode contains two similar 20 Ampere diodes; you just need to connect the two outer terminals of the case to each other. Now we have a full 40 Ampere diode. The diode will need to be installed on a sufficiently large heat sink, since the latter will overheat quite strongly; a small cooler may be needed.
The operation of the transformer is based on converting current from a 220 V network. The devices are divided by the number of phases, as well as the overload indicator. Modifications of single-phase and two-phase types are available on the market. The current overload parameter ranges from 3 to 10 A. If necessary, you can make an electronic transformer with your own hands. However, to do this, it is first important to familiarize yourself with the structure of the model.
Model diagram
The electronic 12V circuit involves the use of a pass relay. The winding itself is used with a filter. To increase the clock frequency, there are capacitors in the circuit. They are available in open and closed types. For single-phase modifications, rectifiers are used. These elements are necessary to increase current conductivity.
On average, the sensitivity of the models is 10 mV. With the help of expanders, problems with network congestion are solved. If we consider a two-phase modification, then it uses a thyristor. The specified element is usually installed with resistors. Their capacity is on average 15 pF. The level of current conduction in this case depends on the relay load.
How to do it yourself?
You can easily do it yourself. For this it is important to use a wired relay. It is advisable to select an expander for it of the pulse type. To increase the sensitivity parameter of the device, capacitors are used. Many experts recommend installing resistors with insulators.
To solve problems with voltage surges, filters are soldered. If we consider a homemade single-phase model, then it is more appropriate to select a modulator for 20 W. The output impedance in the transformer circuit should be 55 Ohms. The output contacts are soldered directly to connect the device.
Devices with capacitor resistor
The electronic transformer circuit for 12V involves the use of a wired relay. In this case, resistors are installed behind the plate. As a rule, modulators are used of the open type. Also, the electronic transformer circuit for 12V halogen lamps includes rectifiers that are matched with filters.
To solve switching problems, amplifiers are needed. The average output resistance is 45 ohms. Current conductivity, as a rule, does not exceed 10 microns. If we consider a single-phase modification, then it has a trigger. Some specialists use triggers to increase conductivity. However, in this case, heat losses increase significantly.
Transformers with regulator
The 220-12 V transformer with a regulator is quite simple. The relay in this case is usually used as a wired type. The regulator itself is installed with a modulator. To solve problems with reverse polarity there is a kenotron. It can be used with or without a cover.
The trigger in this case is connected through conductors. These elements can only work with pulse expanders. On average, the conductivity parameter of transformers of this type does not exceed 12 microns. It is also important to note that the negative resistance value depends on the sensitivity of the modulator. As a rule, it does not exceed 45 Ohms.
Using wire stabilizers
A 220-12 V transformer with a wire stabilizer is very rare. For normal operation of the device, a high-quality relay is necessary. The negative resistance indicator is on average 50 ohms. The stabilizer in this case is fixed on the modulator. This element is primarily intended to lower the clock frequency.
The heat losses from the transformer are insignificant. However, it is important to note that there is a lot of pressure on the trigger. Some experts recommend using capacitive filters in this situation. They are sold with or without a guide.
Models with diode bridge
A transformer (12 Volt) of this type is made on the basis of selective triggers. The threshold resistance of the models is on average 35 Ohms. To solve problems with frequency reduction, transceivers are installed. Directly diode bridges are used with different conductivities. If we consider single-phase modifications, then in this case the resistors are selected for two plates. The conductivity indicator does not exceed 8 microns.
Tetrodes in transformers can significantly increase the sensitivity of the relay. Modifications with amplifiers are very rare. The main problem with this type of transformers is negative polarity. It occurs due to an increase in the temperature of the relay. To remedy the situation, many experts recommend using triggers with conductors.
Model Taschibra
The electronic transformer circuit for 12V halogen lamps includes a trigger with two plates. The model's relay is of the wired type. To solve problems with reduced frequency, expanders are used. In total, the model has three capacitors. Therefore, network congestion problems rarely occur. On average, the output resistance parameter is kept at 50 Ohms. According to experts, the output voltage at the transformer should not exceed 30 W. On average, the sensitivity of the modulator is 5.5 microns. However, in this case it is important to take into account the load on the expander.
Device RET251C
The specified electronic transformer for lamps is produced with an output adapter. The model has a dipole type expander. There are a total of three capacitors installed in the device. A resistor is used to solve problems with negative polarity. The model's capacitors rarely overheat. The modulator is directly connected through a resistor. In total, the model has two thyristors. First of all, they are responsible for the output voltage parameter. Thyristors are also designed to ensure stable operation of the expander.
Transformer GET 03
The transformer (12 Volt) of this series is very popular. In total, the model has two resistors. They are located next to the modulator. If we talk about indicators, it is important to note that the modification frequency is 55 Hz. The device is connected via an output adapter.
The expander is matched with an insulator. To solve problems with negative polarity, two capacitors are used. There is no regulator in the presented modification. The conductivity index of the transformer is 4.5 microns. The output voltage fluctuates around 12 V.
Device ELTR-70
The specified 12V electronic transformer includes two pass-through thyristors. A distinctive feature of the modification is the high clock frequency. Thus, the current conversion process will be carried out without voltage surges. The model's expander is used without lining.
There is a trigger to reduce sensitivity. It is installed as a standard selective type. The negative resistance indicator is 40 ohms. For a single-phase modification this is considered normal. It is also important to note that the devices are connected via an output adapter.
Model ELTR-60
This transformer features high voltage stability. The model refers to single-phase devices. It uses a capacitor with high conductivity. Problems with negative polarity are solved by using an expander. It is installed behind the modulator. There is no regulator in the presented transformer. In total, the model uses two resistors. Their capacitance is 4.5 pF. According to experts, overheating of elements is observed very rarely. The output voltage to the relay is strictly 12 V.
Transformers TRA110
These transformers operate from a pass-through relay. The model’s expanders are used in different capacities. The average output impedance of the transformer is 40 ohms. The model belongs to two-phase modifications. Its threshold frequency is 55 Hz. In this case, dipole type resistors are used. In total, the model has two capacitors. To stabilize the frequency during operation of the device, a modulator operates. The conductors of the model are soldered with high conductivity.
How to power a cordless screwdriver from an electrical outlet?
The cordless screwdriver is designed for screwing and unscrewing screws, self-tapping screws, screws and bolts. It all depends on the use of replaceable heads - bits. The scope of application of a screwdriver is also very wide: it is used by furniture assemblers, electricians, construction workers - finishers use it to secure plasterboard slabs and, in general, everything that can be assembled using a threaded connection.
This is the use of a screwdriver in a professional setting. In addition to professionals, this tool is also purchased exclusively for personal use when carrying out repair and construction work in an apartment or country house, or garage.
The cordless screwdriver is lightweight, small in size, and does not require a power connection, which allows you to work with it in any conditions. But the trouble is that the battery capacity is small, and after 30 - 40 minutes of intensive work you have to charge the battery for at least 3 - 4 hours.
In addition, batteries tend to become unusable, especially when the screwdriver is not used regularly: they hung up a carpet, curtains, pictures and put it in a box. A year later, we decided to screw in a plastic baseboard, but the screwdriver didn’t work, and charging the battery didn’t help much.
A new battery is expensive, and it’s not always possible to immediately find exactly what you need on sale. In both cases, there is only one way out - to power the screwdriver from the mains through the power supply. Moreover, most often the work is carried out two steps away from a power outlet. The design of such a power supply will be described below.
In general, the design is simple, does not contain scarce parts, and can be repeated by anyone who is at least a little familiar with electrical circuits and knows how to hold a soldering iron in their hands. If we remember how many screwdrivers are in use, we can assume that the design will be popular and in demand.
The power supply must satisfy several requirements at once. Firstly, it is quite reliable, and secondly, it is small-sized and light and convenient to carry and transport. The third requirement, perhaps the most important, is a falling load characteristic, which allows you to avoid damage to the screwdriver during overloads. Simplicity of design and availability of parts are also important. All these requirements are fully met by the power supply, the design of which will be discussed below.
The basis of the device is an electronic transformer of the Feron or Toshibra brand with a power of 60 watts. Such transformers are sold in electrical goods stores and are designed to power halogen lamps with a voltage of 12 V. Typically, such lamps are used to illuminate shop windows.
In this design, the transformer itself does not require any modifications; it is used as is: two input network wires and two output wires with a voltage of 12 V. The circuit diagram of the power supply is quite simple and is shown in Figure 1.
Figure 1. Schematic diagram of the power supply
Transformer T1 creates a falling characteristic of the power supply due to increased leakage inductance, which is achieved by its design, which will be discussed above. In addition, transformer T1 provides additional galvanic isolation from the network, which increases the overall electrical safety of the device, although this isolation is already present in the electronic transformer U1 itself. By selecting the number of turns of the primary winding, it is possible to regulate the output voltage of the unit as a whole within certain limits, which allows it to be used with different types of screwdrivers.
The secondary winding of transformer T1 is tapped from the midpoint, which makes it possible to use a full-wave rectifier with only two diodes instead of a diode bridge. Compared to a bridge circuit, the losses of such a rectifier, due to the voltage drop across the diodes, are two times lower. After all, there are two diodes, not four. In order to further reduce power losses on diodes, a diode assembly with Schottky diodes is used in the rectifier.
Low-frequency ripples of the rectified voltage are smoothed out by electrolytic capacitor C1. Electronic transformers operate at high frequencies, about 40 - 50 KHz, therefore, in addition to ripples at the mains frequency, these high-frequency ripples are also present in the output voltage. Considering that the full-wave rectifier increases the frequency by 2 times, these ripples reach 100 kilohertz or more.
Oxide capacitors have a large internal inductance, so they cannot smooth out high-frequency ripples. Moreover, they will simply uselessly heat up the electrolytic capacitor, and may even render it unusable. To suppress these ripples, a ceramic capacitor C2 is installed in parallel with the oxide capacitor, with a small capacitance and a small self-inductance.
Indication of the operation of the power supply can be checked by the lighting of the HL1 LED, the current through which is limited by resistor R1.
Separately, it should be said about the purpose of resistors R2 - R7. The fact is that the electronic transformer was originally designed to power halogen lamps. It is assumed that these lamps are connected to the output winding of the electronic transformer even before it is connected to the network: otherwise it simply does not start without a load.
If, in the design described, you plug in the electronic transformer into the network, then pressing the screwdriver button again will not make it rotate. To prevent this from happening, resistors R2 - R7 are provided in the design. Their resistance is chosen such that the electronic transformer starts up reliably.
Details and design
The power supply is housed in the housing of a standard battery that has expired, unless, of course, it has already been thrown away. The basis of the design is an aluminum plate with a thickness of at least 3 mm, placed in the middle of the battery case. The overall design is shown in Figure 2.
Figure 2. Power supply for cordless screwdriver
All other parts are attached to this plate: electronic transformer U1, transformer T1 (on one side), and the diode assembly VD1 and all other parts, including the power button SB1, on the other. The plate also serves as a common output voltage wire, so the diode assembly is installed on it without a gasket, although for better cooling the heat-removing surface of the VD1 assembly should be lubricated with heat-removing paste KPT-8.
Transformer T1 is made on a ferrite ring of standard size 28*16*9 made of HM2000 ferrite. Such a ring is not in short supply, it is quite common, and there should be no problems with its acquisition. Before winding the transformer, first, using a diamond file or just sandpaper, you should blunt the outer and inner edges of the ring, and then insulate it with varnished cloth tape or FUM tape, used for winding heating pipes.
As mentioned above, the transformer must have a large leakage inductance. This is achieved by the fact that the windings are located opposite each other, and not one under the other. Primary winding I contains 16 turns of two wires of PEL or PEV-2 grade. Wire diameter 0.8 mm.
Secondary winding II is wound with a bundle of four wires, the number of turns is 12, the wire diameter is the same as for the primary winding. To ensure symmetry of the secondary winding, it should be wound into two wires at once, or rather a bundle. After winding, as is usually done, the beginning of one winding is connected to the end of the other. To do this, the windings will have to be “ringed” with a tester.
The MP3-1 microswitch is used as the SB1 button, which has a normally closed contact. A pusher is installed in the bottom of the power supply housing, which is connected to a button through a spring. The power supply is connected to the screwdriver, exactly the same as a standard battery.
If you now place the screwdriver on a flat surface, the pusher presses the SB1 button through a spring and the power supply turns off. As soon as the screwdriver is picked up, the released button will turn on the power supply. All you have to do is pull the screwdriver trigger and everything will work.
A little about the details
There are few parts in the power supply. It is better to use imported capacitors; this is now even easier than finding domestically produced parts. The VD1 diode assembly of type SBL2040CT (rectified current 20 A, reverse voltage 40 V) can be replaced with SBL3040CT, or, in extreme cases, with two domestic KD2997 diodes. But the diodes indicated in the diagram are not in short supply, since they are used in computer power supplies, and buying them is not a problem.
The design of transformer T1 was discussed above. Any LED you have on hand will work as an HL1 LED.
Setting up the device is simple and comes down to simply unwinding the turns of the primary winding of transformer T1 to achieve the desired output voltage. The rated supply voltage of screwdrivers, depending on the model, is 9, 12 and 19 V. By unwinding the turns from transformer T1, 11, 14 and 20 V should be achieved, respectively.
Externally electronic transformer It is a small metal, usually aluminum, case, the halves of which are fastened together with only two rivets. However, some companies produce similar devices in plastic cases.
To see what's inside, these rivets can simply be drilled out. The same operation will have to be performed if alteration or repair of the device itself is planned. Although, given its low price, it is much easier to go and buy another one than to repair the old one. And yet, there were many enthusiasts who not only managed to understand the structure of the device, but also developed several switching power supplies based on it.
A schematic diagram is not included with the device, as with all current electronic devices. But the circuit is quite simple, contains a small number of parts, and therefore the circuit diagram of an electronic transformer can be copied from a printed circuit board.
Figure 1 shows a diagram of a Taschibra transformer taken in a similar way. Converters manufactured by Feron have a very similar circuit. The only difference is in the design of the printed circuit boards and the types of parts used, mainly transformers: in Feron converters the output transformer is made on a ring, while in Taschibra converters it is on an W-shaped core.
In both cases, the cores are made of ferrite. It should be immediately noted that ring-shaped transformers, with various modifications of the device, are better rewindable than W-shaped ones. Therefore, if an electronic transformer is purchased for experiments and modifications, it is better to buy a device from Feron.
When using an electronic transformer only to power halogen lamps, the name of the manufacturer does not matter. The only thing you should pay attention to is the power: electronic transformers are available with a power of 60 - 250 W.
Figure 1. Diagram of an electronic transformer from Taschibra
Brief description of the electronic transformer circuit, its advantages and disadvantages
As can be seen from the figure, the device is a push-pull self-oscillator made according to a half-bridge circuit. The two arms of the bridge are made of transistors Q1 and Q2, and the other two arms contain capacitors C1 and C2, so this bridge is called a half bridge.
One of its diagonals is supplied with mains voltage, rectified by a diode bridge, and the other is connected to the load. In this case, this is the primary winding of the output transformer. Electronic ballasts for energy-saving lamps are made according to a very similar scheme, but instead of a transformer they include a choke, capacitors and filaments of fluorescent lamps.
To control the operation of the transistors, windings I and II of the feedback transformer T1 are included in their basic circuits. Winding III is the current feedback; the primary winding of the output transformer is connected through it.
The control transformer T1 is wound on a ferrite ring with an outer diameter of 8 mm. Basic windings I and II contain 3..4 turns each, and feedback winding III contains only one turn. All three windings are made of wires in multi-colored plastic insulation, which is important when experimenting with the device.
The elements R2, R3, C4, D5, D6 assemble the circuit for starting the autogenerator at the moment the entire device is connected to the network. The mains voltage rectified by the input diode bridge charges capacitor C4 through resistor R2. When the voltage across it exceeds the operating threshold of dinistor D6, the latter opens and a current pulse is formed at the base of transistor Q2, which starts the converter.
Further work is carried out without the participation of the starting circuit. It should be noted that the D6 dinistor is double-sided and can operate in alternating current circuits; in the case of direct current, the polarity of the connection does not matter. On the Internet it is also called “diak”.
The mains rectifier is made of four 1N4007 type diodes, resistor R1 with a resistance of 1 Ohm and a power of 0.125 W is used as a fuse.
The converter circuit as it is is quite simple and does not contain any “excesses”. After the rectifier bridge there is not even a simple capacitor provided to smooth out the ripples of the rectified mains voltage.
The output voltage directly from the output winding of the transformer is also supplied directly to the load without any filters. There are no circuits for stabilizing the output voltage and protection, so in the event of a short circuit in the load circuit, several elements burn out at once, as a rule, these are transistors Q1, Q2, resistors R4, R5, R1. Well, maybe not all at once, but at least one transistor for sure.
And despite this seemingly imperfection, the scheme fully justifies itself when used in normal mode, i.e. for powering halogen lamps. The simplicity of the circuit determines its low cost and widespread use of the device as a whole.
Study of the operation of electronic transformers
If you connect a load to an electronic transformer, for example, a 12V x 50W halogen lamp, and connect an oscilloscope to this load, then on its screen you will see the picture shown in Figure 2.
Figure 2. Oscillogram of the output voltage of the Taschibra 12Vx50W electronic transformer
The output voltage is a high-frequency oscillation with a frequency of 40KHz, modulated 100% by a frequency of 100Hz, obtained after rectifying the mains voltage with a frequency of 50Hz, which is quite suitable for powering halogen lamps. Exactly the same picture will be obtained for converters of a different power or from a different company, because the circuits are practically no different from each other.
If you connect an electrolytic capacitor C4 47uFx400V to the output of the rectifier bridge, as shown by the dotted line in Figure 4, then the voltage at the load will take the form shown in Figure 4.
Figure 3. Connecting a capacitor to the output of the rectifier bridge
However, we should not forget that the charging current of the additionally connected capacitor C4 will lead to the burnout, and quite noisy, of resistor R1, which is used as a fuse. Therefore, this resistor should be replaced with a more powerful resistor with a rating of 22Ohmx2W, the purpose of which is simply to limit the charging current of capacitor C4. As a fuse, you should use a regular 0.5A fuse.
It is easy to see that the modulation with a frequency of 100 Hz has ceased, leaving only high-frequency oscillations with a frequency of about 40 kHz. Even if during this study it is not possible to use an oscilloscope, this indisputable fact can be noticed by a slight increase in the brightness of the light bulb.
This suggests that the electronic transformer is quite suitable for creating simple switching power supplies. There are several options here: using the converter without disassembling, only by adding external elements and with minor changes to the circuit, very small, but giving the converter completely different properties. But we will talk about this in more detail in the next article.
How to make a power supply from an electronic transformer?
After everything that has been said in the previous article (see How does an electronic transformer work?), it seems that making a switching power supply from an electronic transformer is quite simple: put a rectifier bridge, a smoothing capacitor, and, if necessary, a voltage stabilizer at the output and connect the load. However, this is not quite true.
The fact is that the converter does not start without a load or the load is not sufficient: if you connect an LED to the output of the rectifier, of course, with a limiting resistor, you will be able to see only one LED flash when turned on.
To see another flash, you will need to turn off and turn on the converter to the network. In order for the flash to turn into a constant glow, you need to connect an additional load to the rectifier, which will simply take away the useful power, turning it into heat. Therefore, this scheme is used in the case where the load is constant, for example, a DC motor or an electromagnet, which can only be controlled via the primary circuit.
If the load requires a voltage of more than 12V, which is produced by electronic transformers, you will need to rewind the output transformer, although there is a less labor-intensive option.
Option for manufacturing a switching power supply without disassembling the electronic transformer
The diagram of such a power supply is shown in Figure 1.
Figure 1. Bipolar power supply for amplifier
The power supply is made on the basis of an electronic transformer with a power of 105W. To manufacture such a power supply, you will need to make several additional elements: a mains filter, matching transformer T1, output choke L2, rectifier bridge VD1-VD4.
The power supply has been operating for several years with a ULF power of 2x20W without any complaints. With a nominal network voltage of 220V and a load current of 0.1A, the output voltage of the unit is 2x25V, and when the current increases to 2A, the voltage drops to 2x20V, which is quite enough for normal operation of the amplifier.
The matching transformer T1 is made on a K30x18x7 ring made of M2000NM ferrite. The primary winding contains 10 turns of PEV-2 wire with a diameter of 0.8 mm, folded in half and twisted into a bundle. The secondary winding contains 2x22 turns with a midpoint, the same wire, also folded in half. To make the winding symmetrical, you should wind it in two wires at once - a bundle. After winding, to obtain the midpoint, connect the beginning of one winding to the end of the other.
You will also have to make the inductor L2 yourself; for its manufacture you will need the same ferrite ring as for the transformer T1. Both windings are wound with PEV-2 wire with a diameter of 0.8 mm and contain 10 turns.
The rectifier bridge is assembled on KD213 diodes, you can also use KD2997 or imported ones, it is only important that the diodes are designed for an operating frequency of at least 100 KHz. If instead of them you put, for example, KD242, then they will only heat up, and you will not be able to get the required voltage from them. The diodes should be installed on a radiator with an area of at least 60 - 70 cm2, using insulating mica spacers.
Electrolytic capacitors C4, C5 are made up of three parallel-connected capacitors with a capacity of 2200 microfarads each. This is usually done in all switching power supplies in order to reduce the overall inductance of the electrolytic capacitors. In addition, it is also useful to install ceramic capacitors with a capacity of 0.33 - 0.5 μF in parallel with them, which will smooth out high-frequency vibrations.
It is useful to install an input surge filter at the input of the power supply, although it will work without it. As an input filter choke, a ready-made DF50GTs choke was used, which was used in 3USTST TVs.
All units of the block are mounted on a board made of insulating material in a hinged manner, using the pins of the parts for this purpose. The entire structure should be placed in a shielding case made of brass or tin, with holes provided for cooling.
A correctly assembled power supply does not require adjustment and starts working immediately. Although, before placing the block in the finished structure, you should check it. To do this, a load is connected to the output of the block - resistors with a resistance of 240 Ohms, with a power of at least 5 W. It is not recommended to turn on the unit without load.
Another way to modify an electronic transformer
There are situations when you want to use a similar switching power supply, but the load turns out to be very “harmful”. The current consumption is either very small or varies widely, and the power supply does not start.
A similar situation arose when they tried to install a lamp or chandelier with built-in electronic transformers instead of halogen lamps. LED. The chandelier simply refused to work with them. What to do in this case, how to make it all work?
To understand this issue, let's look at Figure 2, which shows a simplified circuit of an electronic transformer.
Figure 2. Simplified circuit of an electronic transformer
Let's pay attention to the winding of the control transformer T1, highlighted by a red stripe. This winding provides current feedback: if there is no current through the load, or it is simply small, then the transformer simply does not start. Some citizens who bought this device connect a 2.5W light bulb to it, and then take it back to the store, saying it doesn’t work.
And yet, in a fairly simple way, you can not only make the device work with virtually no load, but also provide short circuit protection in it. The method of such modification is shown in Figure 3.
Figure 3. Modification of the electronic transformer. Simplified diagram.
In order for the electronic transformer to operate without load or with minimal load, current feedback should be replaced with voltage feedback. To do this, remove the current feedback winding (highlighted in red in Figure 2), and instead solder a jumper wire into the board, naturally, in addition to the ferrite ring.
Next, a winding of 2 - 3 turns is wound onto the control transformer Tr1, this is the one on the small ring. And there is one turn per output transformer, and then the resulting additional windings are connected as indicated in the diagram. If the converter does not start, then you need to change the phasing of one of the windings.
The resistor in the feedback circuit is selected within the range of 3 - 10 Ohms, with a power of at least 1 W. It determines the depth of feedback, which determines the current at which generation will fail. Actually, this is the current of short-circuit protection. The greater the resistance of this resistor, the lower the load current the generation will fail, i.e. short circuit protection triggered.
Of all the improvements given, this is perhaps the best. But this will not prevent you from supplementing it with another transformer, as in the circuit in Figure 1.
Electronic transformers: purpose and typical use
Application of electronic transformer
In order to improve the electrical safety conditions of lighting systems, in some cases it is recommended to use lamps not with a voltage of 220V, but much lower. As a rule, such lighting is installed in damp rooms: basements, cellars, bathrooms.
For these purposes, they are currently mainly used halogen lamps with operating voltage 12V. These lamps are powered through electronic transformers, the internal structure of which will be discussed a little later. In the meantime, a few words about the normal use of these devices.
Externally, the electronic transformer is a small metal or plastic box from which 4 wires come out: two input wires labeled ~220V, and two output wires ~12V.
Everything is quite simple and clear. Electronic transformers allow brightness adjustment using dimmers(thyristor regulators) of course from the input voltage side. It is possible to connect several electronic transformers to one dimmer at once. Naturally, switching on without regulators is also possible. Typical circuit diagram for connecting an electronic transformer shown in Figure 1.
Figure 1. Typical circuit diagram for connecting an electronic transformer.
The advantages of electronic transformers, first of all, include their small dimensions and weight, which allows them to be installed almost anywhere. Some models of modern lighting devices designed to work with halogen lamps contain built-in electronic transformers, sometimes even several of them. This scheme is used, for example, in chandeliers. There are known options when electronic transformers are installed in furniture to provide internal lighting for shelves and hangers.
For indoor lighting, transformers can be installed behind a suspended ceiling or behind plasterboard wall coverings in close proximity to halogen lamps. At the same time, the length of the connecting wires between the transformer and the lamp is no more than 0.5 - 1 meter, which is due to high currents (at a voltage of 12V and a power of 60W, the current in the load is at least 5A), as well as the high-frequency component of the output voltage of the electronic transformer.
The inductive reactance of a wire increases with frequency and also with its length. Basically, the length determines the inductance of the wire. In this case, the total power of the connected lamps should not exceed that indicated on the label of the electronic transformer. To increase the reliability of the entire system as a whole, it is better if the power of the lamps is 10 - 15% lower than the power of the transformer.
Rice. 2. Electronic transformer for halogen lamps from OSRAM
That's probably all that can be said about the typical use of this device. There is one condition that should not be forgotten: electronic transformers do not start without load. Therefore, the light bulb must be permanently connected, and the lighting must be turned on with a switch installed in the primary network.
But the scope of application of electronic transformers is not limited to this: simple modifications, often without even requiring opening the case, make it possible to create switching power supplies (UPS) based on an electronic transformer. But before talking about this, you should take a closer look at the structure of the transformer itself.
In the next article we will take a closer look at one of the electronic transformers from Taschibra, and also conduct a small study of the operation of the transformer.
Transformers for halogen lamps
Spot recessed lamps Today they have become the same everyday normal thing in the interior of a house, apartment, or office as an ordinary chandelier or fluorescent lamp.
Many people have probably noticed that sometimes light bulbs, if there are several of them, glow differently in these same spotlights. Some lamps shine quite brightly, while others burn, at best, at half incandescence. In this article we will try to understand the essence of the problem.
So, first, a little theory. Halogen bulbs installed in recessed spotlights are designed for operating voltages of 220 V and 12 V. In order to connect light bulbs designed for a voltage of 12 V, a special transformer device is required.
Transformers for halogen lamps presented on our market are mostly electronic. There are also toroidal transformers, but in this article we will not dwell on them. Let us only note that they are more reliable than electronic ones, but provided that you have a relatively stable voltage and the power of the transformer-lamp is correctly balanced.
An electronic transformer for halogen lamps has a number of advantages compared to a conventional transformer. These advantages include: soft start (not all trans have it), short circuit protection (also not all), light weight, small size, constant output voltage (most), automatic adjustment of the output voltage. But all this will work correctly only with proper installation.
It just so happens that many self-taught electricians or people who lay wires read few books on electrical engineering, much less the instructions that come with almost all devices, in this case step-down transformers. In this very instruction it is written in black and white that:
1) the length of the wire from the transformer to the lamp should be no more than 1.5 meters, provided that the cross-section of the wire is at least 1 mm square.
2) if it is necessary to connect 2 or more lamps to one transformer, the connection is made according to the “star” circuit;
3) if you need to increase the length of the wire from the transformer to the lamp, then it is necessary to increase the cross-section of the wire in proportion to the length;
Following these simple rules will save you from many questions and problems that arise during the lighting installation process.
Without going too much into the laws of physics, let’s consider each of the points.
1) If you increase the length of the wires, the lamp will shine more dimly, and the wire may begin to heat up.
2) What is a star circuit? This means that a separate wire should be drawn to each lamp and, importantly, the length of all wires should be the same length, regardless of the distance transformer->lamp, otherwise the glow of all lamps will be different.
4) Each transformer for halogen lamps is designed for a certain power. There is no need to take a 300 W transformer and power a 20 W light bulb onto it.
Firstly, it’s pointless and secondly, there will be no coordination between the transformer and the lamp, and something from this chain will definitely burn out. It's just a matter of time.
For example, for a transformer with a power of 105 W, you can use 3 lamps of 35 W, 5 of 20 W, but this is subject to the use of high-quality transformers.
The reliability of a transformer largely depends on the manufacturer. Most of the electrical equipment presented on our market is manufactured, you know where, in China. The price, as a rule, corresponds to the quality. When choosing a transformer, carefully read the instructions (if any), or what is written on the box or the transformer itself.
As a rule, the manufacturer writes the maximum power that this device is capable of. In practice, it is necessary to subtract about 30% from this figure, then there is a chance that the transformer will last for some time.
If all the wiring has already been done and it is not possible to redo the wiring according to the “star” circuit, the best option would be to power each light bulb with its own separate transformer. At first, this will cost a little more than one trans for 3-4 lamps, but later, during operation, you will understand the advantages of this scheme.
What is the advantage? If one transformer fails, only one light bulb will not shine, which, you see, is quite convenient, because the main lighting still remains in operation.
If you need to regulate the light intensity, that is, use a dimmer, you will have to abandon the electronic transformer, since most electronic transformers are not designed to work with a dimmer. In this case, you can use a toroidal step-down transformer.
If it seems a little expensive for you to “hang” a separate transformer on each light bulb, instead of light bulbs designed for 12 V, install 220 V lamps, equipping them with a soft start device, or, if the design of the lamps allows, change the lamps to others, to For example, MR-16 LED economy lamps. We described this in more detail in a previous article.
When choosing a transformer for halogen light bulbs, opt for high-quality, more expensive transformers. Such transformers are equipped with a variety of protections: against short circuits, against overheating, and are equipped with a soft start device for lamps, which significantly extends the life of the lamps by 2-3 times. And, in addition, high-quality transformers undergo many checks for operational safety, fire safety, and compliance with European standards, which cannot be said about cheaper models, which, for the most part, appear from nowhere.
In any case, it is better to entrust all rather complex technical issues, which include the choice of transformers for halogen lamps, to professionals.
Device for smooth switching on of incandescent lamps
The operating principle of this device and the advantages of using it.
As is known, incandescent lamps and the so-called halogen lamps very often they fail. This is often due to unstable mains voltage and very frequent switching on of the lamps. Even if low-voltage lamps (12 volts) are used through a step-down transformer, frequent switching on of the lamps still leads to their rapid combustion. For a longer service life of incandescent lamps, a device for smooth switching on of lamps was invented.
A device for soft starting of incandescent lamps ignites the lamp filament more slowly (2-3 seconds), thereby eliminating the possibility of lamp failure at the moment the filament is heated.
As is known in most cases incandescent lamps fail at the moment of switching on, by eliminating this moment, we will significantly extend the service life of incandescent lamps.
It is also necessary to take into account that when passing through the device for smooth switching of lamps, the network voltage stabilizes, and the lamp is not affected by sudden voltage surges.
Soft starters for lamps can be used with both 220-volt lamps and lamps operating through a step-down transformer. In both cases, the device for smoothly switching on lamps is installed in an open circuit (phase).
Please remember that when using the device in conjunction with step-down transformer, it must be installed before the transformer.
You can install the device for smooth switching of lamps in any accessible place, be it a junction box, a chandelier connector, a switch, or a recessed lamp.
It is not recommended to install in rooms with high humidity. Each individual device must be selected depending on the load that it will support; a soft-start device cannot be installed for lamps with an installed power lower than that of all the lamps it protects. You cannot use the device for smooth switching of lamps with fluorescent lamps.
By installing a device for smooth switching of lamps, you will forget for a long time about the problem of replacing halogen and incandescent lamps.
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Many novice radio amateurs, and not only those, face problems in the manufacture of powerful power supplies. Nowadays a large number of electronic transformers have appeared on sale, used to power halogen lamps. The electronic transformer is a half-bridge self-oscillating pulse voltage converter. experience in remaking the electronic transformer Taschibra 105W.
Let's consider the circuit diagram of an electronic converter. half-bridge converter based on transistors Q1 and Q2. In the diagonal of the bridge formed by these transistors and capacitors C1, C2, winding I of the pulse transformer T2 is turned on. Starting the inverter is provided by a circuit consisting of resistors R1, R2, capacitor C3, diode D5 and diac D6. Transformer feedback T1 has three windings - the current feedback winding, which is connected in series with the primary winding of the power transformer, and two windings of 3 turns, feeding the base circuits of the transistors. 30 kHz modulated at 100 Hz.
In order to use an electronic transformer as a power source, it must be finalize.
We connect a capacitor at the output of the rectifier bridge to smooth out the ripples of the rectified voltage. The capacitance is selected at the rate of 1 µF per 1 W. The operating voltage of the capacitor should not be less than 400V. When a rectifier bridge with a capacitor is connected to the network, an inrush current occurs, so you need to break turn on one of the network wires an NTC thermistor or a 4.7 Ohm 5W resistor. This will limit the starting current.
If a different output voltage is needed, we rewind the secondary winding of the power transformer. The diameter of the wire (harness of wires) is selected based on the load current.
Electronic transformers are current feedback, so the output voltage will vary depending on from the load. If the load is not connected, the transformer will not start. In order for this not to happen, it is necessary change the current feedback circuit to the voltage feedback circuit. We remove the current feedback winding and replace it with a jumper on the board. Then we skip flexible stranded wire through a power transformer and make 2 turns, then pass the wire through feedback transformer and make one turn. The ends passed through a power transformer and the feedback transformer wires, we connect through two parallel connected resistors 6.8 Ohm 5 W. This current-limiting resistor sets the conversion frequency (approximately 30 kHz). As the load current increases, the frequency becomes higher. If the converter does not start, you need to change the winding direction.
In Taschibra transformers, the transistors are pressed to the housing through cardboard, which is unsafe during operation. In addition, paper conducts heat very poorly. Therefore, it is better to install transistors through a heat-conducting gasket install a diode bridge. KD213B (200V; 10A; 100 kHz; 0.17 µs). At high load currents they heat up, so they need to be install on the radiator through heat-conducting gaskets. For normal operation, a smooth startup of the device is necessary. Helps ensure smooth starting throttle L1. Together with a 100uF capacitor, it also performs the function of filtering rectified voltage. Such cores (yellow, with one white edge) are used in computer power supplies. External diameter 27mm, internal 14mm, and height 12mm. By the way, in dead power supplies you can also find other parts, including a thermistor. If you have a screwdriver or other tool whose battery has exhausted its resource, then a power supply from an electronic transformer can be placed in the housing of this battery. As a result, you will have a network-powered tool.
During the process of setting up a transformer, you need to be extremely careful and careful. There is high voltage on the device elements. Do not touch the transistor flanges, to check if they are heating up or not. It is also necessary to remember that after switching off the capacitors remain charged for some time. |
Experiments with electronic transformer "Tashibra"
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I think that the advantages of this transformer have already been appreciated by many of those who have ever dealt with the problems of powering various electronic structures. And this electronic transformer has many advantages. Light weight and dimensions (as with all similar circuits), ease of modification to suit your own needs, the presence of a shielding housing, low cost and relative reliability (at least, if extreme modes and short circuits are avoided, a product made according to a similar circuit can work long years). The range of application of power supplies based on "Tashibra" can be very wide, comparable to the use of conventional transformers.
The use is justified in cases of shortage of time, funds, or lack of need for stabilization.
Well, shall we experiment? Let me make a reservation right away that the purpose of the experiments was to test the Tashibra starting circuit under various loads, frequencies and the use of various transformers. I also wanted to select the optimal ratings of the components of the PIC circuit and check the temperature conditions of the circuit components when operating under various loads, taking into account the use of the “Tashibra” case as a radiator.
Despite the large number of published electronic transformer circuits, I will not be too lazy to once again post it for review. Look at Fig.1, illustrating the "Tashibra" filling.
The diagram is valid for ET "Tashibra" 60-150W. The mockery was carried out on ET 150W. It is assumed, however, that due to the identity of the circuits, the results of the experiments can be easily projected onto instances of both lower and higher power.
And let me remind you once again what Tashibra is missing for a full-fledged power supply.
1. Lack of an input smoothing filter (also an anti-interference filter, which prevents conversion products from entering the network),
2. Current PIC, which allows excitation of the converter and its normal operation only in the presence of a certain load current,
3. No output rectifier,
4. Lack of output filter elements.
Let's try to correct all of the listed shortcomings of "Tashibra" and try to achieve its acceptable operation with the desired output characteristics. To begin with, we won’t even open the housing of the electronic transformer, but simply add the missing elements...
1. Input filter: capacitors C`1, C`2 with a symmetrical two-winding choke (transformer) T`1
2. diode bridge VDS`1 with smoothing capacitor C`3 and resistor R`1 to protect the bridge from the charging current of the capacitor.
The smoothing capacitor is usually selected at the rate of 1.0 - 1.5 μF per watt of power, and a discharge resistor with a resistance of 300-500 kOhm should be connected in parallel to the capacitor for safety (touching the terminals of a capacitor charged with a relatively high voltage is not very pleasant).
Resistor R`1 can be replaced with a 5-15Ohm/1-5A thermistor. Such a replacement will reduce the efficiency of the transformer to a lesser extent.
At the output of the ET, as shown in the diagram in Fig. 3, we connect a circuit of diode VD`1, capacitors C`4-C`5 and inductor L1 connected between them to obtain a filtered DC voltage at the “patient” output. In this case, the polystyrene capacitor placed directly behind the diode accounts for the main share of absorption of conversion products after rectification. It is assumed that the electrolytic capacitor, “hidden” behind the inductance of the inductor, will perform only its direct functions, preventing voltage “dip” at the peak power of the device connected to the ET. But it is also recommended to install a non-electrolytic capacitor in parallel with it.
After adding the input circuit, changes occurred in the operation of the electronic transformer: the amplitude of the output pulses (up to the diode VD`1) increased slightly due to the increase in the voltage at the input of the device due to the addition of C`3, and modulation with a frequency of 50 Hz was practically absent. This is at the load calculated for the electric vehicle.
However, this is not enough. "Tashibra" does not want to start without significant load current.
Installing load resistors at the output of the converter to create any minimum current value capable of starting the converter only reduces the overall efficiency of the device. Starting at a load current of about 100 mA is carried out at a very low frequency, which will be quite difficult to filter if the power supply is intended for joint use with UMZCH and other audio equipment with low current consumption in the no-signal mode, for example. The amplitude of the pulses is also less than at full load. The change in frequency in different power modes is quite strong: from a couple to several tens of kilohertz. This circumstance imposes significant restrictions on the use of "Tashibra" in this (for now) form when working with many devices.
But let's continue.
There have been proposals to connect an additional transformer to the ET output, as shown, for example, in Fig. 2.
It was assumed that the primary winding of the additional transformer is capable of creating a current sufficient for the normal operation of the basic ET circuit. The offer, however, is tempting only because without disassembling the electric transformer, using an additional transformer you can create a set of necessary (to your liking) voltages. In fact, the no-load current of the additional transformer is not enough to start the electric vehicle. Attempts to increase the current (such as a 6.3VX0.3A light bulb connected to an additional winding) capable of ensuring NORMAL operation of the ET only resulted in the converter starting up and the light bulb lighting up. But perhaps someone will be interested in this result, because... connecting an additional transformer is also true in many other cases to solve many problems. So, for example, an additional transformer can be used in conjunction with an old (but working) computer power supply, capable of providing significant output power, but having a limited (but stabilized) set of voltages.
One could continue to search for the truth in the shamanism around "Tashibra", however, I considered this topic exhausted for myself, because to achieve the desired result (stable start-up and return to operating mode in the absence of load, and, therefore, high efficiency; a slight change in frequency when the power supply is operating from minimum to maximum power and stable start-up at maximum load) it is much more effective to get inside the Tashibra "and make all the necessary changes in the circuit of the ET itself in the manner shown in Fig. 4. Moreover,
I collected about fifty similar circuits back in the era of Spectrum computers (specifically for these computers). Various UMZCHs, powered by similar power supplies, are still working somewhere. PSUs made according to this scheme showed their best performance, working while being assembled from a wide variety of components and in various options.
Are we redoing it? Certainly. Moreover, it is not at all difficult.
We solder the transformer. We warm it up for ease of disassembly in order to rewind the secondary winding to obtain the desired output parameters as shown in this photo
or using any other technology. In this case, the transformer is soldered only in order to inquire about its winding data (by the way: W-shaped magnetic core with a round core, standard dimensions for computer power supplies with 90 turns of the primary winding, wound in 3 layers with a wire with a diameter of 0.65 mm and 7 turns secondary winding with a wire folded five times with a diameter of approximately 1.1 mm; all this without the slightest interlayer and interwinding insulation - just varnish) and make room for another transformer. For experiments, it was easier for me to use ring magnetic cores. They take up less space on the board, which makes it possible (if necessary) to use additional components in the volume of the case. In this case, a pair of ferrite rings with outer and inner diameters and heights of 32x20x6mm, respectively, folded in half (without gluing) - N2000-NM1 - was used. 90 turns of the primary (wire diameter - 0.65 mm) and 2X12 (1.2 mm) turns of the secondary with the necessary inter-winding insulation. The communication winding contains 1 turn of mounting wire with a diameter of 0.35 mm. All windings are wound in the order corresponding to the numbering of the windings. Insulation of the magnetic circuit itself is mandatory. In this case, the magnetic circuit is wrapped in two layers of electrical tape, by the way, securely fixing the folded rings.
Before installing the transformer on the ET board, we unsolder the current winding of the commutating transformer and use it as a jumper, soldering it there, but without passing the transformer rings through the window. We install the wound transformer Tr2 on the board, soldering the leads in accordance with the diagram in Fig. 4
and pass the wire of winding III into the window of the commutating transformer ring. Using the rigidity of the wire, we form a semblance of a geometrically closed circle and the feedback loop is ready. In the gap in the mounting wire that forms windings III of both (switching and power) transformers, we solder a fairly powerful resistor (>1W) with a resistance of 3-10 Ohms.
In the diagram in Fig. 4, standard ET diodes are not used. They should be removed, as should resistor R1, in order to increase the efficiency of the unit as a whole. But you can neglect a few percent of the efficiency and leave the listed parts on the board. At least at the time of the experiments with ET, these parts remained on the board. The resistors installed in the base circuits of the transistors should be left - they perform the functions of limiting the base current when starting the converter, facilitating its operation on a capacitive load.
Transistors should definitely be installed on radiators through insulating heat-conducting gaskets (borrowed, for example, from a faulty computer power supply), thereby preventing them
accidental instant heating and providing some personal safety in case of touching the radiator while the device is operating. By the way, the electrical cardboard used in ET to insulate transistors and the board from the case is not thermally conductive. Therefore, when “packing” the finished power supply circuit into a standard case, exactly these gaskets should be installed between the transistors and the case. Only in this case will at least some heat removal be ensured. When using a converter with powers over 100W, an additional radiator must be installed on the device body. But this is for the future.
In the meantime, having finished installing the circuit, let’s perform one more safety point by connecting its input in series through an incandescent lamp with a power of 150-200W. The lamp, in the event of an emergency (short circuit, for example), will limit the current through the structure to a safe value and, in the worst case, create additional illumination of the work space. In the best case, with some observation, the lamp can be used as an indicator, for example, of through current. Thus, a weak (or somewhat more intense) glow of the lamp filament with an unloaded or lightly loaded converter will indicate the presence of a through current. The temperature of the key elements can serve as confirmation - heating in through-current mode will be quite fast. When a working converter is operating, the glow of a 200-watt lamp filament, visible against the background of daylight, will appear only at the threshold of 20-35 W.
So, everything is ready for the first launch of the converted "Tashibra" circuit. To begin with, we turn it on - without load, but do not forget about the pre-connected voltmeter to the output of the converter and an oscilloscope. With correctly phased feedback windings, the converter should start without problems. If the start-up does not occur, then we pass the wire passed through the window of the commutating transformer (having previously unsoldered it from resistor R5) on the other side, giving it, again, the appearance of a completed turn. Solder the wire to R5. Apply power to the converter again. Did not help? Look for errors in installation: short circuit, “missing connections”, erroneously set values.
When a working converter is started with the specified winding data, the display of an oscilloscope connected to the secondary winding of transformer Tr2 (in my case, half of the winding) will display a time-invariant sequence of clear rectangular pulses. The conversion frequency is selected by resistor R5 and in my case, with R5 = 5.1Ohm, the frequency of the unloaded converter was 18 kHz. With a load of 20 Ohm - 20.5 kHz. With a load of 12 Ohm - 22.3 kHz. The load was connected directly to the instrument-controlled winding of the transformer with an effective voltage value of 17.5V. The calculated voltage value was slightly different (20V), but it turned out that instead of the nominal value of 5.1 Ohm, the resistance installed on the board R1 = 51 Ohm. Be attentive to such surprises from your Chinese comrades. However, I considered it possible to continue the experiments without replacing this resistor, despite its significant but tolerable heating. When the power delivered by the converter to the load was about 25 W, the power dissipated by this resistor did not exceed 0.4 W.
As for the potential power of the power supply, at a frequency of 20 kHz the installed transformer will be able to deliver no more than 60-65 W to the load.
Let's try to increase the frequency. When the resistor (R5) with a resistance of 8.2 Ohm is turned on, the frequency of the converter without load increases to 38.5 kHz, with a load of 12 Ohm - 41.8 kHz.
At this conversion frequency, with the existing power transformer, you can safely service a load of up to 120 W.
You can further experiment with the resistances in the PIC circuit, achieving the required frequency value, keeping in mind, however, that too high a resistance R5 can lead to generation failures and unstable startup of the converter. When changing the parameters of the PIC converter, you should control the current passing through the converter keys.
You can also experiment with the PIC windings of both transformers at your own peril and risk. In this case, you should first calculate the number of turns of the commutating transformer using the formulas posted on the page /stats/Blokpit02.htm, for example, or using one of Mr. Moskatov’s programs posted on the page of his website /Design_tools_pulse_transformers.html.
You can avoid heating resistor R5 by replacing it... with a capacitor.
In this case, the PIC circuit certainly acquires some resonant properties, but no deterioration in the operation of the power supply is manifested. Moreover, a capacitor installed instead of a resistor heats up significantly less than the replaced resistor. Thus, the frequency with a 220nF capacitor installed increased to 86.5 kHz (without load) and amounted to 88.1 kHz when operating with a load. Startup and operation
the converter remained as stable as in the case of using a resistor in the PIC circuit. Note that the potential power of the power supply at such a frequency increases to 220 W (minimum).
Transformer power: values are approximate, with certain assumptions, but not exaggerated.
Unfortunately, I did not have the opportunity to test a power supply with a large load current, but I believe that the description of the experiments performed is enough to draw the attention of many to such simple power converter circuits, worthy of use in a wide variety of designs .
I apologize in advance for possible inaccuracies, omissions and errors. I'll correct myself in answering your questions.
How to make a switching power supply from a burnt-out light bulb in an hour?
In this article you will find a detailed description of the process of manufacturing switching power supplies of different powers based on the electronic ballast of a compact fluorescent lamp.
You can make a switching power supply for 5...20 Watts in less than an hour. It will take several hours to make a 100-watt power supply./
Building a power supply won't be much more difficult than reading this article. And certainly, it will be easier than finding a low-frequency transformer of suitable power and rewinding its secondary windings to suit your needs.
Introduction.
The difference between a CFL circuit and a pulse power supply.
What power power supply can be made from CFLs?
Pulse transformer for power supply.
Input filter capacitance and voltage ripple.
20 Watt power supply.
100 watt power supply
Rectifier.
How to properly connect a switching power supply to the network?
How to set up a switching power supply?
What is the purpose of the switching power supply circuit elements?
Introduction.
Compact Fluorescent Lamps (CFLs) are now widely used. To reduce the size of the ballast choke, they use a high-frequency voltage converter circuit, which can significantly reduce the size of the choke.
If the electronic ballast fails, it can be easily repaired. But when the bulb itself fails, the light bulb is usually thrown away.
However, the electronic ballast of such a light bulb is an almost ready-made switching power supply unit (PSU). The only way the electronic ballast circuit differs from a real pulse power supply is the absence of an isolation transformer and a rectifier, if necessary./
At the same time, modern radio amateurs experience great difficulty in finding power transformers to power their homemade products. Even if a transformer is found, its rewinding requires the use of a large amount of copper wire, and the weight and dimensions of products assembled on the basis of power transformers are not encouraging. But in the vast majority of cases, the power transformer can be replaced with a switching power supply. If you use ballast from faulty CFLs for these purposes, the savings will amount to a significant amount, especially if we are talking about transformers of 100 watts or more.
Experiments with the tashibra electronic transformer. Electronic transformer circuit
Such an interesting component, like an electronic transformer, is begging for a variety of amateur radio crafts. It costs only a couple of dollars and can easily be purchased and converted into a power supply or compact car charger. Today we will tell you how to make a power supply from an electronic transformer.
The basis of our power supply will be a Chinese electronic transformer with short circuit protection called Taschibra, with a power of 105 W, the diagram of which is shown below.
It is almost impossible to use it as a regular power supply without modifications. The main problem is that the output of the electronic transformer is high frequency alternating voltage. Also, such a transformer is not capable of operating without a minimum load.
We will tell you about a conversion method in which the electronic transformer does not even have to be disassembled, just connect a small board to its output. In the diagram, its components are highlighted with a red frame.
It consists of a diode (a Schottky diode and a filter capacitor are required). To start the unit, a small light bulb must be connected to its output.
How to choose a Schottky diode. The first step is to know the output voltage of the electronic transformer. As a rule, it is 12 V, as well as the maximum current, for our transformer it will be about 8 A. Depending on these parameters, the Schottky diode is selected.
You need to select a diode with a maximum reverse voltage at least 3 times higher than the voltage at the output of the electronic transformer. In terms of current, it is better to choose a diode whose direct current is at least 1.5 times greater than the maximum output from your power supply.
This is roughly what our board looks like.
As you can see, the power supply from the electronic transformer is working, and at the output we already have a constant smoothed current. If you have the desire and opportunity, then it is better to create a higher-quality filter and not be limited to just one electrolytic capacitor at the output. Also, during operation, transistors and a Schottky diode must be installed on the radiator.
Where to use such a powerful power supply from an electronic transformer is up to you to decide. Of course, it is not suitable for powering receivers or high-quality amplifiers, but it can easily cope with an LED strip, a small motor or other undemanding devices.
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Remaking an electronic transformer
An electronic transformer is a network switching power supply, which is designed to power 12 Volt halogen lamps. Read more about this device in the article “Electronic transformer (introduction)”. The device has a fairly simple circuit. A simple push-pull self-oscillator, which is made using a half-bridge circuit, the operating frequency is about 30 kHz, but this indicator strongly depends on the output load. The circuit of such a power supply is very unstable, it does not have any protection against short circuits at the output of the transformer, perhaps precisely because of this, the circuit has not yet found widespread use in amateur radio circles. Although recently there has been a promotion of this topic on various forums. People offer various options for modifying such transformers. Today I will try to combine all these improvements in one article and offer options not only for improvements, but also for strengthening the ET.
We won’t go into the basics of how the circuit works, but let’s get down to business right away. We will try to refine and increase the power of the Chinese Taschibra electric vehicle by 105 watts.
To begin with, I want to explain why I decided to take on the powering and alteration of such transformers. The fact is that recently a neighbor asked me to make him a custom-made charger for a car battery that would be compact and lightweight. I didn’t want to assemble it, but later I came across interesting articles that discussed remaking an electronic transformer. This gave me the idea - why not try it?
Thus, several ETs from 50 to 150 Watts were purchased, but experiments with conversion were not always completed successfully; of all, only the 105 Watt ET survived. The disadvantage of such a block is that its transformer is not ring-shaped, and therefore it is inconvenient to unwind or rewind the turns. But there was no other choice and this particular block had to be remade.
As we know, these units do not turn on without load; this is not always an advantage. I plan to get a reliable device that can be freely used for any purpose without fear that the power supply may burn out or fail during a short circuit.
Improvement No. 1
The essence of the idea is to add short-circuit protection and also eliminate the above-mentioned drawback (activation of a circuit without an output load or with a low-power load).
Looking at the unit itself, we can see the simplest UPS circuit; I would say that the circuit has not been fully developed by the manufacturer. As we know, if you short-circuit the secondary winding of a transformer, the circuit will fail in less than a second. The current in the circuit increases sharply, the switches instantly fail, and sometimes even the basic limiters. Thus, repairing the circuit will cost more than the cost (the price of such an ET is about $2.5).
The feedback transformer consists of three separate windings. Two of these windings power the base switch circuits.
First, remove the communication winding on the OS transformer and install a jumper. This winding is connected in series with the primary winding of the pulse transformer. Then we wind only 2 turns on the power transformer and one turn on the ring (OS transformer). For winding, you can use a wire with a diameter of 0.4-0.8 mm.
Next, you need to select a resistor for the OS, in my case it is 6.2 ohms, but a resistor can be selected with a resistance of 3-12 ohms, the higher the resistance of this resistor, the lower the short-circuit protection current. In my case, the resistor is a wirewound one, which I do not recommend doing. We select the power of this resistor to be 3-5 watts (you can use from 1 to 10 watts).
During a short circuit on the output winding of a pulse transformer, the current in the secondary winding drops (in standard ET circuits, during a short circuit, the current increases, disabling the switches). This leads to a decrease in the current on the OS winding. Thus, generation stops and the keys themselves are locked.
The only drawback of this solution is that in the event of a long-term short circuit at the output, the circuit fails because the switches heat up quite strongly. Do not expose the output winding to a short circuit lasting more than 5-8 seconds.
The circuit will now start without load; in a word, we have a full-fledged UPS with short-circuit protection.
Improvement No. 2
Now we will try to smooth out the mains voltage from the rectifier to some extent. For this we will use chokes and a smoothing capacitor. In my case, a ready-made inductor with two independent windings was used. This inductor was removed from the UPS of the DVD player, although homemade inductors can also be used.
After the bridge, an electrolyte with a capacity of 200 μF should be connected with a voltage of at least 400 Volts. The capacitor capacity is selected based on the power of the power supply 1 μF per 1 watt of power. But as you remember, our power supply is designed for 105 Watts, why is the capacitor used at 200 μF? You will understand this very soon.
Improvement No. 3
Now about the main thing - increasing the power of the electronic transformer and is it real? In fact, there is only one reliable way to power it up without much modification.
For powering up, it is convenient to use an ET with a ring transformer, since it will be necessary to rewind the secondary winding; it is for this reason that we will replace our transformer.
The network winding is stretched across the entire ring and contains 90 turns of wire 0.5-0.65 mm. The winding is wound on two folded ferrite rings, which were removed from an ET with a power of 150 watts. The secondary winding is wound based on needs, in our case it is designed for 12 Volts.
It is planned to increase the power to 200 watts. That is why an electrolyte with a reserve, which was mentioned above, was needed.
We replace the half-bridge capacitors with 0.5 μF; in the standard circuit they have a capacity of 0.22 μF. Bipolar keys MJE13007 are replaced with MJE13009. The power winding of the transformer contains 8 turns, the winding was done with 5 strands of 0.7 mm wire, so we have a wire in the primary with a total cross-section of 3.5 mm.
Go ahead. Before and after the chokes we place film capacitors with a capacity of 0.22-0.47 μF with a voltage of at least 400 Volts (I used exactly those capacitors that were on the ET board and which had to be replaced to increase the power).
Next, replace the diode rectifier. In standard circuits, conventional rectifier diodes of the 1N4007 series are used. The current of the diodes is 1 Ampere, our circuit consumes a lot of current, so the diodes should be replaced with more powerful ones in order to avoid unpleasant results after the first turn on of the circuit. You can use literally any rectifier diodes with a current of 1.5-2 Amps, a reverse voltage of at least 400 Volts.
All components except the generator board are mounted on a breadboard. The keys were secured to the heat sink through insulating gaskets.
We continue our modification of the electronic transformer, adding a rectifier and filter to the circuit. The chokes are wound on rings made of powdered iron (removed from a computer power supply unit) and consist of 5-8 turns. It is convenient to wind it using 5 strands of wire with a diameter of 0.4-0.6 mm each.
We select a smoothing capacitor with a voltage of 25-35 Volts; one powerful Schottky diode (diode assemblies from a computer power supply) is used as a rectifier. You can use any fast diodes with a current of 15-20 Amps.
AKA KASYAN
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Chinese electronic transformer TASCHIBRA TRA25
Review of the popular Chinese electronic transformer TASCHIBRA. One fine day, a friend of mine brought a pulsed electronic transformer for repair to power the halogen lamps used to power it. The repair was a quick replacement of the dinistor. After giving it to the owner. I had a desire to make the same block for myself. First, I found out where he bought it and bought it for later copying.
Technical characteristics of TASCHIBRA TRA25
- Input AC 220V 50/60 Hz.
- AC 12V output. 60W MAX.
- Protection class 1.
Electronic transformer circuit
A more detailed diagram can be viewed here. List of parts for manufacturing:
- n-p-n transistor 13003 2 pcs.
- Diode 1N4007 4 pcs.
- Film capacitor 10nF 100V 1 piece (C1).
- Film capacitor 47nF 250V 2 pcs (C2, C3).
- Dinistor DB3
- Resistors:
- R1 22 ohm 0.25W
- R2 500 kOhm 0.25W
- R3 2.5 ohm 0.25W
- R4 2.5 ohm 0.25W
Manufacturing a transformer on an W-shaped ferrite core from a computer power supply.
The primary winding contains a 1-core wire with a diameter of 0.5 mm, a length of 2.85 m and 68 turns. The standard secondary winding contains a 4-core wire with a diameter of 0.5 mm, a length of 33 cm and 8-12 turns. The windings of the transformer must be wound in one direction. Winding the inductor on a ferrite ring with a diameter of 8 mm of the coil: 4 turns of green wire, 4 turns of yellow wire and not a full 1 (0.5) turn of red wire.
PCB photo and PCB file.
Dinistor DB3 and its characteristics:
- (I open - 0.2 A), V 5 is the voltage when open;
- Average maximum permissible value when open: A 0.3;
- In the open state, the pulse current is A 2;
- Maximum voltage (during closed state): V 32;
- Current in closed state: µA - 10; The maximum non-unlocking pulse voltage is 5 V.
This is how the design turned out. The view is certainly not very good, but I was convinced that you can assemble this switching power supply device yourself.
radioskot.ru
Experiments with electronic transformer tashibra CAVR.ru
Share in: I think that the advantages of this transformer have already been appreciated by many of those who have ever dealt with the problems of powering various electronic structures. And this electronic transformer has many advantages. Light weight and dimensions (as with all similar circuits), ease of modification to suit your own needs, the presence of a shielding housing, low cost and relative reliability (at least, if extreme modes and short circuits are avoided, a product made according to a similar circuit can work long years). The range of application of power supplies based on "Tashibra" can be very wide, comparable to the use of conventional transformers. The use is justified in cases of shortage of time, money, and lack of need for stabilization. Well, shall we experiment? Let me make a reservation right away that the purpose of the experiments was to test the Tashibra starting circuit under various loads, frequencies and the use of various transformers. I also wanted to select the optimal ratings of the PIC circuit components and check the temperature conditions of the circuit components when operating under various loads, taking into account the use of the “Tashibra” case as a radiator. Despite the large number of published electronic transformer circuits, I will not be too lazy to once again put it on display. Look at Fig.1, illustrating the "Tashibra" filling.
The diagram is valid for ET "Tashibra" 60-150W. The mockery was carried out on ET 150W. It is assumed, however, that due to the identity of the circuits, the results of the experiments can easily be projected onto copies with both lower and higher power. And let me remind you once again what Tashibra lacks for a full-fledged power supply. 1. Lack of an input smoothing filter (also known as an anti-interference filter, which prevents conversion products from entering the network), 2. Current PIC, which allows excitation of the converter and its normal operation only in the presence of a certain load current, 3. Lack of output rectifier,4. Lack of output filter elements. Let's try to correct all of the listed shortcomings of "Tashibra" and try to achieve its acceptable operation with the desired output characteristics. To begin with, we won’t even open the housing of the electronic transformer, but simply add the missing elements...
1. Input filter: capacitors C`1, C`2 with a symmetrical two-winding choke (transformer) T`12. diode bridge VDS`1 with smoothing capacitor C`3 and resistor R`1 to protect the bridge from the charging current of the capacitor.
The smoothing capacitor is usually selected at the rate of 1.0 - 1.5 µF per watt of power, and a discharge resistor with a resistance of 300-500 kOhm should be connected in parallel to the capacitor for safety (touching the terminals of a capacitor charged with a relatively high voltage is not very pleasant). Resistor R`1 can replace with a 5-15Ohm/1-5A thermistor. Such a replacement will reduce the efficiency of the transformer to a lesser extent. At the output of the ET, as shown in the diagram in Fig. 3, we connect a circuit of diode VD`1, capacitors C`4-C`5 and inductor L1 connected between them - to obtain a filtered DC voltage at the exit of the "patient". In this case, the polystyrene capacitor placed directly behind the diode accounts for the main share of absorption of conversion products after rectification. It is assumed that the electrolytic capacitor, “hidden” behind the inductance of the inductor, will perform only its direct functions, preventing voltage “dip” at the peak power of the device connected to the ET. But it is also recommended to install a non-electrolytic capacitor in parallel with it.
After adding the input circuit, changes occurred in the operation of the electronic transformer: the amplitude of the output pulses (up to the diode VD`1) increased slightly due to the increase in the voltage at the input of the device due to the addition of C`3, and modulation with a frequency of 50 Hz was practically absent. This is at the load calculated for the electric vehicle. However, this is not enough. "Tashibra" does not want to start without a significant load current. Installing load resistors at the output of the converter to create any minimum current value capable of starting the converter only reduces the overall efficiency of the device. Starting at a load current of about 100 mA is carried out at a very low frequency, which will be quite difficult to filter if the power supply is intended for joint use with UMZCH and other audio equipment with low current consumption in the no-signal mode, for example. The amplitude of the pulses is also less than at full load. The change in frequency in different power modes is quite strong: from a couple to several tens of kilohertz. This circumstance imposes significant restrictions on the use of "Tashibra" in this (for now) form when working with many devices. But let's continue. There have been proposals to connect an additional transformer to the output of the ET, as is shown, for example, in Fig. 2.
It was assumed that the primary winding of the additional transformer is capable of creating a current sufficient for the normal operation of the basic ET circuit. The offer, however, is tempting only because without disassembling the electric transformer, using an additional transformer you can create a set of necessary (to your liking) voltages. In fact, the no-load current of the additional transformer is not enough to start the electric vehicle. Attempts to increase the current (such as a 6.3VX0.3A light bulb connected to an additional winding) capable of ensuring NORMAL operation of the ET only resulted in the converter starting up and the light bulb lighting up. But perhaps someone will be interested in this result, because... connecting an additional transformer is also true in many other cases to solve many problems. So, for example, an additional transformer can be used in conjunction with an old (but working) computer power supply, capable of providing significant output power, but having a limited (but stabilized) set of voltages.
One could continue to search for the truth in the shamanism around "Tashibra", however, I considered this topic exhausted for myself, because to achieve the desired result (stable start-up and return to operating mode in the absence of load, and, therefore, high efficiency; a slight change in frequency when the power supply is operating from minimum to maximum power and stable start-up at maximum load) it is much more effective to get inside the Tashibra " and make all the necessary changes in the circuit of the ET itself in the manner shown in Fig. 4. Moreover, I collected fifty similar circuits back in the era of Spectrum computers (precisely for these computers). Various UMZCHs, powered by similar power supplies, are still working somewhere. PSUs made according to this scheme showed their best performance, working while being assembled from a wide variety of components and in various options.
Are we redoing it? Certainly. Moreover, it is not at all difficult.
We solder the transformer. We warm it up for ease of disassembly in order to rewind the secondary winding to obtain the desired output parameters as shown in this photo
or using any other technology. In this case, the transformer is soldered only in order to inquire about its winding data (by the way: W-shaped magnetic core with a round core, standard dimensions for computer power supplies with 90 turns of the primary winding, wound in 3 layers with a wire with a diameter of 0.65 mm and 7 turns secondary winding with a wire folded five times with a diameter of approximately 1.1 mm; all this without the slightest interlayer and interwinding insulation - just varnish) and make room for another transformer. For experiments, it was easier for me to use ring magnetic cores. They take up less space on the board, which makes it possible (if necessary) to use additional components in the volume of the case. In this case, a pair of ferrite rings with outer and inner diameters and heights of 32x20x6mm, respectively, folded in half (without gluing) - N2000-NM1 - was used. 90 turns of the primary (wire diameter - 0.65 mm) and 2X12 (1.2 mm) turns of the secondary with the necessary inter-winding insulation. The communication winding contains 1 turn of mounting wire with a diameter of 0.35 mm. All windings are wound in the order corresponding to the numbering of the windings. Insulation of the magnetic circuit itself is mandatory. In this case, the magnetic circuit is wrapped in two layers of electrical tape, by the way, securely fixing the folded rings.
Before installing the transformer on the ET board, we unsolder the current winding of the commutating transformer and use it as a jumper, soldering it there, but without passing the transformer rings through the window. We install the wound transformer Tr2 on the board, soldering the leads in accordance with the diagram in Fig. 4
and pass the wire of winding III into the window of the commutating transformer ring. Using the rigidity of the wire, we form a semblance of a geometrically closed circle and the feedback loop is ready. In the gap in the mounting wire that forms windings III of both (switching and power) transformers, we solder a fairly powerful resistor (>1W) with a resistance of 3-10 Ohms.
In the diagram in Fig. 4, standard ET diodes are not used. They should be removed, as should resistor R1, in order to increase the efficiency of the unit as a whole. But you can neglect a few percent of the efficiency and leave the listed parts on the board. At least at the time of the experiments with ET, these parts remained on the board. Resistors installed in the base circuits of transistors should be left - they perform the functions of limiting the base current when starting the converter, facilitating its operation on a capacitive load. Transistors should certainly be installed on radiators through insulating heat-conducting gaskets (borrowed, for example, from a faulty computer power supply), thereby preventing most of them
accidental instant heating and providing some personal safety in case of touching the radiator while the device is operating. By the way, the electrical cardboard used in ET to insulate transistors and the board from the case is not thermally conductive. Therefore, when “packing” the finished power supply circuit into a standard case, exactly these gaskets should be installed between the transistors and the case. Only in this case will at least some heat removal be ensured. When using a converter with powers over 100W, an additional radiator must be installed on the device body. But this is for the future. In the meantime, having finished installing the circuit, let’s perform one more safety point by connecting its input in series through an incandescent lamp with a power of 150-200 W. The lamp, in the event of an emergency (short circuit, for example), will limit the current through the structure to a safe value and, in the worst case, create additional illumination of the work space. In the best case, with some observation, the lamp can be used as an indicator, for example, of through current. Thus, a weak (or somewhat more intense) glow of the lamp filament with an unloaded or lightly loaded converter will indicate the presence of a through current. The temperature of the key elements can serve as confirmation - heating in through-current mode will be quite fast. When a working converter is operating, the glow of a 200-watt lamp filament, visible against the background of daylight, will appear only at the threshold of 20-35 W. So, everything is ready for the first start-up of the converted “Tashibra” circuit. To begin with, we turn it on - without load, but do not forget about the pre-connected voltmeter to the output of the converter and an oscilloscope. With correctly phased feedback windings, the converter should start without problems. If the start-up does not occur, then we pass the wire passed through the window of the commutating transformer (having previously unsoldered it from resistor R5) on the other side, giving it, again, the appearance of a completed turn. Solder the wire to R5. Apply power to the converter again. Did not help? Look for errors in installation: short circuit, “missing connections”, erroneously set values. When you start a working converter with the specified winding data, the display of an oscilloscope connected to the secondary winding of transformer Tr2 (in my case - to half the winding) will display a time-invariant sequence of clear rectangular pulses. The conversion frequency is selected by resistor R5 and in my case, with R5 = 5.1Ohm, the frequency of the unloaded converter was 18 kHz. With a load of 20 Ohm - 20.5 kHz. With a load of 12 Ohm - 22.3 kHz. The load was connected directly to the instrument-controlled winding of the transformer with an effective voltage value of 17.5V. The calculated voltage value was slightly different (20V), but it turned out that instead of the nominal value of 5.1 Ohm, the resistance installed on the board R1 = 51 Ohm. Be attentive to such surprises from your Chinese comrades. However, I considered it possible to continue the experiments without replacing this resistor, despite its significant but tolerable heating. When the power delivered by the converter to the load was about 25 W, the power dissipated by this resistor did not exceed 0.4 W. As for the potential power of the power supply, at a frequency of 20 kHz the installed transformer will be able to deliver no more than 60-65 W to the load. Let's try to increase the frequency. When the resistor (R5) with a resistance of 8.2 Ohm is turned on, the frequency of the converter without load increases to 38.5 kHz, with a load of 12 Ohm - 41.8 kHz.
At this conversion frequency, with the existing power transformer you can safely service a load with a power of up to 120 W. You can experiment further with resistances in the PIC circuit, achieving the required frequency value, keeping in mind, however, that too high a resistance R5 can lead to generation failures and unstable startup of the converter . When changing the parameters of the PIC converter, you should control the current passing through the converter keys. You can also experiment with the PIC windings of both transformers at your own peril and risk. In this case, you should first calculate the number of turns of the commutating transformer using the formulas posted on the page http://interlavka.narod.ru/stats/Blokpit02.htm, for example, or using one of Mr. Moskatov’s programs posted on the page of his website http://www.moskatov.narod.ru/Design_tools_pulse_transformers.html.You can avoid heating resistor R5 by replacing it... with a capacitor.
In this case, the PIC circuit certainly acquires some resonant properties, but no deterioration in the operation of the power supply is manifested. Moreover, a capacitor installed instead of a resistor heats up significantly less than the replaced resistor. Thus, the frequency with a 220nF capacitor installed increased to 86.5 kHz (without load) and amounted to 88.1 kHz when operating with a load. Startup and operation 
the converter remained as stable as in the case of using a resistor in the PIC circuit. Note that the potential power of a power supply at such a frequency increases to 220 W (minimum). Transformer power: values are approximate, with certain assumptions, but not overestimated. Unfortunately, I did not have the opportunity to test a power supply with a large load current, but, I believe that the description of the experiments performed is enough to draw the attention of many to such simple circuits of power converters, worthy of use in a wide variety of designs.
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device, principle of operation and conversion into a power supply with your own hands
Fluorescent and halogen lamps are gradually becoming a thing of the past, giving way to LED lamps. In the lamps where they were used, unnecessary electronic transformers remained, which were responsible for igniting these lamps. It seems that what is unnecessary belongs in the trash heap. But that's not true. These transformers can be used to create powerful power supplies that can power power tools, LED strips, and much more.
Electronic transformer device
The massive transformers we are accustomed to have recently begun to be replaced by electronic ones, which are cheap and compact. The dimensions of the electronic transformer are so small that they are built into the housings of compact fluorescent lamps (CFLs).
All such transformers are made according to the same circuit; the differences between them are minimal. The circuit is based on a symmetrical self-oscillator, otherwise called a multivibrator.
They consist of a diode bridge, transistors and two transformers: matching and power. These are the main parts of the scheme, but not all. In addition to them, the circuit includes various resistors, capacitors and diodes.
Schematic diagram of an electronic transformer.
In this circuit, direct current from the diode bridge is supplied to the autogenerator transistors, which pump energy into the power transformer. The ratings and type of all radio components are selected so that a strictly defined voltage is obtained at the output.
If you turn on such a transformer without a load, the self-generator will not start and there will be no voltage at the output.
DIY assembly according to the diagram
Electronic ballast can be bought in a store or found in your bins, but the most interesting option would be to assemble an electronic transformer with your own hands. It is assembled quite simply, and most of the necessary parts can be picked out from broken power supplies and energy-saving lamps.
- Required components: A diode bridge with a reverse voltage of at least 400 V and a current of at least 3 A or four diodes with the same characteristics.
- 5 A fuse.
- Symmetrical dinistor DB3.
- Resistor 500 kOhm.
- 2 resistors 2.2 Ohm, 0.5 W.
- 2 bipolar transistors MJE13009.
- 3 film capacitors 600 V, 100 nF.
- 2 toroidal cores.
- Lacquered wire 0.5 mm².
- Wire in regular insulation 2.5 mm².
- Radiator for transistors.
- Bread board.
It all starts with a breadboard on which you will install all the radio components. You can buy two types of boards on the market - with one-sided metallization on brown fiberglass.
And with two-way through, on green.
The choice of board determines how much time and effort you will spend on assembling the project.
Brown boards are of disgusting quality. The metallization on them is made in such a thin layer that breaks are visible in some places. It is poorly wetted by solder, even if you use good flux. And everything that was successfully soldered comes off along with the metallization at the slightest effort.
Green ones cost one and a half to two times more, but the quality is okay. Metallization on them has no problems with thickness. All holes in the board are tinned at the factory, so the copper does not oxidize and there are no problems during soldering.
You can find and buy these breadboards either in the nearest radio store or on Aliexpress. In China they cost half as much, but delivery will have to wait.
Choose radio components with long leads, they will be useful to you when installing the circuit. If you are going to use used parts, be sure to check their functionality and absence of external damage.
The only part you have to make yourself is the transformer.
The matching must be wound with a thin wire. Number of turns in each winding:
- I - 7 turns.
- II - 7.
- III - 3.
Don't forget to secure the windings with tape, otherwise they will fall apart.
The power transformer consists of only two windings. Wind the primary with 0.5mm² wire, and the secondary with 2.5mm². The primary and secondary consist of 90 and 12 turns, respectively.
For soldering, it is better not to use “old-fashioned” soldering irons - they can easily burn temperature-sensitive radioelements. It’s better to take a soldering iron with power control; they don’t overheat, unlike the first ones.
Install the transistors on the radiators in advance. Doing this on an already assembled board is extremely inconvenient. You need to assemble the circuit from small parts to large ones. If you install the large ones first, they will interfere when soldering the small ones. Take this into account.
When assembling, look at the circuit diagram; all connections of radio elements must correspond to it. Insert the pins of the parts into the holes on the board and bend them in the desired direction. If the length is not enough, extend them with wire. After soldering, glue the transformers to the board with epoxy resin.
After assembly, connect a load to the terminals of the device and make sure that it works.
Conversion into a power supply
It happens that power tool batteries fail, and there is no opportunity to buy a new one. In this case, an adapter in the form of a power supply will help. After a little modification, you can assemble such an adapter from an electronic transformer.
Parts needed for remodeling:
- NTC thermistor 4 Ohm.
- Capacitor 100 µF, 400 V.
- Capacitor 100 uF, 63V.
- Film capacitor 100 nF.
- 2 resistors 6.8 Ohm, 5 W.
- Resistor 500 Ohm, 2 W.
- 4 diodes KD213B.
- Radiator for diodes.
- Toroidal core.
- Wire with a cross-section of 1.2 mm².
- A piece of circuit board.
Before work, check if you forgot any part. If all the parts are in place, begin converting the electronic transformer into a power supply.
Solder a 400 V, 100 µF capacitor to the output of the diode bridge. To reduce the charging current of the capacitor, solder a thermistor into the gap in the power wire. If you forget to do this, the first time you turn it on, your diode bridge will burn out.
Disconnect the second winding of the matching transformer and replace it with a jumper. Add one winding on both transformers. Make one turn on the matching one, two on the power one. Connect the windings to each other by soldering two parallel-connected 6.8 Ohm resistors into the wire gap.
To make a choke, wind 24 turns of 1.2 mm² wire around the core and secure it with tape. Then, on the breadboard, assemble the remaining radio components according to the diagram and connect the assembly to the main circuit. Don't forget to install diodes on the radiator; they get very hot when operating under load.
Secure the entire structure in any suitable case and the power supply can be considered assembled.
After final assembly, plug the device into the network and check its operation. It should produce a voltage of 12 volts. If the power supply supplies them, you have done your job perfectly. If it doesn't work, check to see if you took a non-working transformer.
220v.guru
UPS from an electronic transformer | Techniques and Programs
September 29, 2012 by admin Comment »I'm generally not much of a fan of making power supplies unless that itself is the purpose of the entire design. However, for about 4 years now, I have been using a regular electronic transformer for halogen lamps as a power supply or even a charger for a car battery. A similar trans can be purchased at any electrical goods store.
There are already some articles on the Internet on converting such trances into a power supply, someone is even intensively researching this device. And in Radio magazine for some year there is an article on this topic. Well, I decided to put in my two cents. In general, everything is simply impossible, making a simpler and more reliable UPS, and even buying parts for it in any hardware store, I think it’s unrealistic. So, the diagram…. The circuit is a regular self-oscillator with current feedback. Those. if there is no load at the output, then essentially the entire electronic transformer does not work. Moreover, the load should be quite decent. There have been cases when I was asked to repair a similar device, saying it didn’t work. At the same time, we connected a 0.25 W light bulb to it and concluded that the device does not light up, they got it in the store. Again, with increasing load, our entire transic successfully turns into coals. Obviously, all this is somehow not particularly suitable for our purposes. We would like to make sure that everything works at idle, and also has protection against short circuits. Oddly enough, all this can be realized by upgrading the simple circuitry of an electronic transformer. Moreover, the answer to how to do this lies on the surface. All you need to do is replace the feedback (feedback) with current and voltage feedback.
The necessary changes are indicated in red on the diagram. The circuit itself may have some variations... for example, the VD1 diode may be missing. We remove the current winding OS, W3 and put a jumper in its place. We wind the feedback winding Woc1 on the main transformer TV1 - 1 turn, Woc2 - 2-3 turns on the feedback transformer Toc (a small ring, for those who don’t know). It is necessary to observe the beginning with the end of the windings, well, if it is not correct, then there is simply no generation. Resistor R4 regulates the OS depth, which in turn affects the current at which the generation of the self-oscillator fails, from where we actually get short-circuit protection. As resistor R4 increases, respectively, at a lower output current, generation will fail. Instead of resistor R4, you can use a film capacitor; this is even more preferable if someone is annoyed by the heating of R4. The capacitor size can be selected from 10n to 330n. It is selected experimentally. The secondary can be wound with a middle point, or a regular one. Then you will need 4 diodes in the rectifier. Diodes, of course, with a Schottky barrier. How much to wind, we are guided by the secondary one that was. I usually remove it completely. Throttle L is not required, but highly desirable. The value is not critical 10... 100 µH. Well, we install C4 electrolyte on the high side, this will improve the quality of the output voltage under load (there will be no ripple, up to a certain limit, of course). You can pick out such a small electrolyte, for example, from an energy-saving light bulb. Oh, and I forgot, you need to put a 220K discharge resistor with a power of 1W on the legs of the electrolyte (in parallel). I forgot to draw it on the diagram (too lazy to finish drawing), it contributes to the accelerated discharge of the electrolyte, and without it the converter may not start after turning it off and quickly turning it on again. This is connected with the DB3 trigger diac. If required, we install voltage stabilizers at the output of the rectifier... in short, who knows what) Well, it is highly advisable to install a surge protector L1, C7, C6. There is a lot of interference from such devices on the network; it’s not at all clear how the Chinese pass the standards via email. compatibility. Apparently there is no way... So, we install a filter. PS: there is no surge protector in the photo, at the time of writing this article it was traveling somewhere across the vast expanses of our country in the form of a parcel.....
nauchebe.net
Electronic transformer: connection diagram
An electronic transformer is an electromagnetic type device. It consists of an inductive winding and a magnetic circuit. An electronic transformer is used to convert alternating current. The devices are found in various electrical appliances.
They are also used to assemble power supplies. Various elements are used to connect the device. In this case, the parameter of threshold voltage, frequency and current conductivity is taken into account. In order to understand everything, you should consider specific schemes.
Connection diagram via capacitor resistor
Any electronic transformer can be connected via a capacitor resistor. The connection diagram includes a modulator as well as a transceiver. The current conductivity of the specified element must be at least 50 microns. In this case, the output voltage depends on the number of resistors. In some cases, expansion transceivers are used. If we consider the model for the power supply, then the amplifier is used as a terminal type. Filters are needed to stabilize the conversion process. Triggers are of the phase type.
Connection via two regulators
Only a low-frequency electronic transformer is allowed to be connected through two regulators. The connection diagram consists of open type tetrodes. In this case, the maximum conductivity of the element is 55 microns. The regulators are installed directly behind the relay. Amplifiers are found in both operational and toroidal types.
For normal operation of the expander, two connectors are used. The trigger capacitance must be at least 2 pF. It is also important to pay attention to the output voltage on the winding. On average, it is no more than 40 V. However, with a high level of negative resistance, this parameter can increase sharply. If we consider the circuit for the power supply, then the thyristor is selected as a dipole type. In this case, the current reducibility parameter of the element is no more than 45 μm. The maximum input voltage can be 20 V. Contactors are used to connect capacitors.
Using wire stabilizers
A high-frequency electronic transformer can be connected through wire stabilizers. The connection diagram assumes the use of triggers with a secondary winding. In this case, tetrodes are installed behind the relay. Filters are used to increase negative resistance. A total of two contactors are required for a 30 W power supply. Resistors are used of the toroidal type. The output voltage of the elements does not exceed 45 V.
Connection to diode bridge
The low-frequency transformer can be connected to the diode bridge through one regulator. For this purpose, the tetrode is used with two filters. The current conductivity of the element must be at least 55 microns. All this will significantly increase the threshold resistance. The modulator for the circuit is selected as a pulse type. If we consider a converter with an amplifier, then the relay must be used only with insulators. In this case, the resistance of the transformer will be about 22 m. The output voltage on the winding will fluctuate around 30 V.
Connection to a halogen lamp
Only a low-frequency electronic transformer may be connected to halogen lamps. The connection diagram consists of dipole type resistors. Capacitors are used with the primary winding. Filters are used to stabilize the induction process. In total, the circuit provides two amplifiers. The relay in this case is installed behind the capacitors.
The expander may only be used in the open type. The current conductivity of the element is 55 microns. Thus, the resistance should not exceed 12 ohms. The output voltage parameter depends on the resistors. If we consider models with a small capacity, then the indicated parameter is about 13 V.
Connection diagram for the Taschibra model
A Taschibra (electronic transformer) can be connected directly via the regulator. The connection diagram assumes the use of a modulator with a primary winding. The transceiver itself for the capacitor is selected for two phases. A Taschibra (electronic transformer) can also be connected via a dipole resistor. The device connection diagram in this case involves the use of a zener diode.
If we consider a standard modulator, then the current conductivity is about 60 microns. In this case, the resistance does not exceed 12 ohms. Wired relays are sometimes used. In this case, the expander is taken without winding.
Connecting the RET251C device
This electronic transformer (circuit RET251C shown below) is connected via two dipole resistors. Capacitors are often used without a modulator. In this case, the input voltage depends on the conductivity parameter. As a rule, it lies within 40 microns. It is also important to note that transistors are used only in the open type. If we consider a low-power converter, then the connector is installed with one amplifier. To connect the expander, two insulators are used. The tetrode can be used with a double regulator.
Transformer connection GET 03
The specified electronic transformer (GET 03 circuit shown below) is connected via a wired relay. The regulator is used with two adapters. The thyristor for connection is taken of the open type. The modulator can be used with or without a winding. If we consider the first option, then the resistor is connected to the selector. In turn, the tetrode is installed of the beam type.
If we consider a circuit without a winding, then the resistor is used only with output contactors. In this case, the regulator is installed behind the relay. An amplifier is not needed in the circuit. The current conductivity indicator will be about 70 microns. Thus, the resistance in the circuit will not exceed 30 Ohms.
Connection diagram for model ELTR-60
This electronic transformer is often used for various power tools. The screwdriver circuit includes an output amplifier. The regulator is used with two transceivers. Thus, the conductivity of the element is at least 44 microns. In this case, the tetrode is of the capacitor type. The output voltage of the transformer depends on the conductivity of the modulator.
If we consider a circuit with a winding, then the capacitor is installed behind the relay. Thus, the current conductivity is 35 microns. The input resistance is no more than 12 ohms. If we consider a circuit without a winding, then we will need to use two expanders. The trigger in this case is used without a filter. The regulator itself is selected as an operational or pulse type.
Connecting the ELTR-70 to a 24 V circuit
The specified electronic transformer (24 volt circuit shown below) is connected through a dipole regulator. In total, the model will require two conductors. The trigger for current conversion is an open type. Also, the connection diagram of the electronic transformer has filters that are installed behind the winding. The tetrode itself is selected for high sensitivity. In the specified circuit, the conductivity parameter should not exceed 60 μ. All this will allow you to keep the output impedance at a stable level.
The transceiver in the circuit is of the low-frequency type. To increase the speed of induction, various amplifiers are used. They are installed with or without capacitors. If we consider the first option, then the relay is used with a secondary winding. When it comes to connecting without capacitors, in this case one transceiver is used.
Connecting transformer TRA110
The connection diagram for the electronic transformer assumes the installation of a wired type regulator. Transceivers are used only in conjunction with dinistors. In total, for normal operation of the model, two capacitors are required. The expander capacitance must be at least 4 pF. In this case, the relay is installed behind the secondary winding.
If we consider a circuit with a trigger, then insulators are required for normal operation of the transformer. The thyristor for it is selected with contactors. If we consider a transformer without a trigger, then in this case it is necessary to install an output type modulator. Its current conductivity must be at least 50 microns. Resistors are used only vector type.
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Currently, there are many power tools that operate on rechargeable batteries. However, after a certain time, the battery life gradually decreases and does not provide the tool with the required power. In such cases, even more frequent charging does not help, so you have to decide what to do next: abandon the unit altogether or switch it to power from the general network. Since a new battery can be compared in price to the tool itself, you can make your own power supply from an electronic transformer, which will cost much less.
Manufacturing specifications
Converting an electronic transformer into a switching power supply is not as simple as it turns out to be in practice. In addition to the transformer, you will need to install a rectifier bridge at the output and a smoothing capacitor. If necessary, also connect the load.
It must be taken into account that the converter cannot be started without a load or with insufficient load. This can be easily checked using an LED connected to the output of the rectifier using a limiting resistor. As a result, the whole thing will end with just one flash of the LED light source at the moment of switching on.
In order for another flash to appear, the converter must first be turned off and then turned on again. It is possible to achieve a constant glow instead of flashes by connecting the rectifier to an additional load, which extracts useful power and releases heat. This circuit can only be used with a constant load controlled through the primary circuit.
If the load requires more than 12 volts supplied by the electronic transformer, it is necessary to rewind the output transformer. There is another option to solve this problem, more effective and less expensive.
How to create a switching power supply without disassembling a transformer
The manufacture of such a power supply is carried out in accordance with the presented diagram. It is based on an electronic transformer with a power of 105 watts. In addition, converting an electronic transformer into a power supply will require the use of additional elements - a rectifier bridge VD1-VD4, an output inductor L2, a matching transformer T1 and a mains filter.
To make a T1 transformer, you will need a ferrite ring with dimensions K30x18x7. The wire in the primary winding is doubled, twisted into a bundle and wound in this form in the amount of 10 turns. A wire with a diameter of 0.8 mm, for example, PEV-2, is best suited. The secondary winding consists of the same wire with the same laying, wound in 2x22 turns. The result is a double symmetrical winding with a common midpoint obtained by connecting the beginning of one winding to the end of the other.
Throttle L2 is also made by hand. It consists of the same ferrite ring as the transformer. For the windings, similar PEV-2 wires are used, wound in 10 turns. The rectifier bridge is assembled using KD213 or KD2997 diodes, which can operate at a minimum operating frequency of 100 kHz. If you use other elements, for example, KD242, they will only heat up, but will not provide the required voltage. The radiator area for installing diodes must be at least 0.6-0.7 m2. The radiator is used together with insulating gaskets.
The chain of electrolytic capacitors C4, C5 includes three 2200 μF elements connected in parallel. This option is used by all switching power supplies in order to reduce the overall inductance of electrolytic capacitors. In some circuits, ceramic capacitors of 0.33-0.5 μF can be connected in parallel with them to smooth out high-frequency oscillations.
The surge protector is installed at the input of the power supply, although the entire system can function without it. The input filter is equipped with a ready-made choke of the DF50GTs brand, which can be taken from the TV. All components and elements of the block are mounted on a common board using the surface-mounting method. Insulating material is used for the board, and the entire finished structure is placed in a brass or tin case with ventilation holes.
If the power supply is correctly assembled, no further adjustment is required, since the device immediately begins to function normally. However, it is still necessary to check the functionality. For this purpose, 240 Ohm resistors and a minimum power of 5 watts are connected at the output of the power supply as a load.
Power supply for use in special conditions
Quite often situations arise when application becomes problematic due to specific operating conditions. This may be too little current consumption or its change over a wide range, as a result, the power supply simply does not start. A typical example is a chandelier in which LED lamps are installed instead of halogen lamps, despite the fact that the lighting device has a built-in electronic transformer. A simplified diagram of this transformer, shown in the figure, will help solve this problem.
In this diagram, the winding of control transformer T1, marked in red, serves to provide current feedback. That is, when the current does not flow through the load or passes in very small quantities, the transformer simply will not turn on. This means that the device will not work if a 2.5 W light bulb is connected to it.
This circuit can be modified, which will allow the device to operate without any load at all. The device will be protected from short circuits. How to do all this in practice is shown in the following figure.
Operation of an electronic transformer with minimal or no load is ensured by replacing current feedback with voltage feedback. For this purpose, the current feedback winding is removed, and in its place a wire jumper is soldered into the board without affecting the ferrite ring.
Then, on the control transformer TR1, installed on a small ring, a winding consisting of 2-3 turns should be wound. Another turn is wound on the output transformer, after which both additional windings are connected. If the device does not start to function, it is recommended to change the phase arrangement on any winding.
The resistor installed in the feedback circuit must have a resistance in the range from 3 to 10 ohms. With its help, the depth of feedback is determined, which determines the value of the current at which generation fails. This will be the response current against a short circuit, depending on the resistance of the resistor.