555 conclusions. Servo as a finger extension

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Modern market electronic components and various devices based on them are mostly filled Chinese manufacturers. Most as protozoa Christmas tree garlands, thermostats, photo relays, and complex household appliances(computers, televisions) are manufactured in China. In addition, delivery from the same is free in most cases, which is why many radio amateurs have already switched to electronic components from China. However, interest in simple designs has not yet disappeared.

The simplest electronic circuits still find their way into home automation systems. Many of them include an integrated timer chip NE555 or its domestic analogue KR1006VI1. Based on the NE555 timer, photo relay circuits, alarm systems, voltage converters and many others are built.

1 Photo relay based on NE555 integrated timer

The photo relay circuit based on the NE555 timer is shown in Figure 1.

Picture 1

The operating algorithm of the circuit is as follows: a change in illumination causes the LS1 light bulb to turn on or off. The presented circuit can be divided into three functional blocks: power supply, load switching block and illumination measurement block.

power unit in the above diagram there is no galvanic isolation of the power supply network and the control circuit. Adjustment of the illumination level at which the light bulb switches is performed once, so constant access to the circuit elements is not required and, accordingly, is not required additional measures to ensure protection against damage electric shock. It is recommended to carry out the setup with a connected external power supply with an output voltage of 12V. The operation of the circuit can be observed by LED1.

The photo relay power supply consists of a diode rectifier Br1 (1N4407), a quenching capacitor C2, a filter capacitor C14, a zener diode D1 (1N4467 or 1N5022A) and a smoothing resistor R5.

Load connection unit is built on the basis of the KR1182PM1A microcircuit, which generates control signals for triac T1 (KU208G or BT139 - 600). The microcircuit control signals are supplied to pins 5 and 6. When pins 5 and 6 are closed (the AOT128 optocoupler transistor is closed), the lamp is disconnected from the network. To adjust the brightness of the lamp, capacitor C13 is used.

Photo relay illuminance meter is based on NE555. A photoresistor LDR1 and a tuning resistor R7 are connected to the input of the timer chip (setting the relay response threshold). Switching of output signals is provided by the NE555 timer. The operating algorithm of the light meter is as follows: the output signals of the timer are determined by the voltage across resistor R7. When the voltage level on R7 is low (the photosensor has not worked and its resistance is high), a high signal level is set at the output of timer 3, the optocoupler is turned off and the transistor is closed, and the light bulb is on. When the resistance of the photosensor decreases, the voltage on R7 increases to a threshold value of 2/3Upit, as a result of which at the timer output - low level voltage. The load switching circuit can be replaced with a simple relay (Figure 2).

Figure 2

To connect a load (light bulb) with a certain time interval relative to turning on the power of the device, you should use the circuit shown in Figure 3 or Figure 4. The figures also show timing diagrams of the circuits (the dotted line shows the supply voltage, the solid line shows the output voltage)

Figure 3

Figure 4

2 Alarm devices based on the NE555 integrated timer chip

2.1 Liquid level indicator(Figure 5)

Figure 5

The liquid level detector circuit based on the NE555 integrated timer is a self-oscillating multivibrator.

The operating principle of the circuit is as follows: two electrodes are immersed in a container of water. If the liquid level is sufficient, both electrodes are immersed in water and the resistance between them is small (capacitor C1 is closed). In this case, the input signals of the timer (pins 2 and 6) are equal to zero, and the output signal (pin 3) is set to a high voltage level and the generator does not work.

A decrease in the liquid level will cause the electrodes to be in the air, and therefore the resistance between them will increase. As a result, capacitor C1 will be connected to the input signals of the microcircuit and the generator will begin to generate pulses. The frequency of the generated pulses is determined by the parameters of the RC circuit.

2.2 Signaling circuit based on NE555 integrated timer(Figure 6)

Figure 6

The timer starts when limit switch S2 is closed. Resetting to the initial state is carried out by contact S1.

Chip timer NE555 includes about 20 transistors, 15 resistors, 2 diodes. Output current is 200 mA, current consumption is approximately 3 mA more. Supply voltage from 4.5 to 18 volts. The accuracy of the timer does not depend on changes in supply voltage and is no more than 1% of the calculated value.

Datasheet of the NE555 chip, as well as a calculator for calculating the harness can be downloaded at the end of the article.

Pin assignment:

Conclusion No. 1 - Earth.

The output is connected to the power supply negative or to the common wire of the circuit.

Conclusion #2 - Launch.

This pin is one of the inputs #2. When a low-level pulse is applied to this input, which should be no more than 1/3 of the supply voltage, the timer starts and voltage appears at pin No. 3 high level for a time set by external resistance Ra+Rb and capacitor C. This mode operation is called monostable mode. The pulse supplied to pin No. 2 can be either rectangular or sinusoidal, and its duration should be less than the charging time of capacitor C.

Conclusion No. 3 - Exit.

The high level is equal to the supply voltage minus 1.7 Volts. Low level is approximately 0.25 volts. The switching time from one level to another occurs in approximately 100 ns.

Conclusion No. 4 - Reset.

When a low level voltage (no more than 0.7V) is applied to this pin, the timer will be reset and a low level voltage will be established at its output. If the circuit does not need a reset mode, then this conclusion must be connected to the power supply.

Conclusion No. 5 - Control.

Typically, this pin is not used. However, its use can significantly expand the functionality of the timer. By applying voltage to this pin, you can control the duration of the output pulses of the timer, which means you can abandon the RC timing chain. The applied voltage to this input in monostable multivibrator mode can range from 45% to 90% of the supply voltage. And in multivibrator mode from 1.7V to the supply voltage. Accordingly, the output will be an FM modulated signal.

If this pin is not used, then it is better to connect it via 0.01 µF to the common wire.

Conclusion #6 - Stop.

This pin is one of the inputs of comparator No. 1. When a high-level pulse (at least 2/3 of the supply voltage) is applied to this pin, the timer operation stops and a low level voltage is set at the timer output. As with pin No. 2, both rectangular and sinusoidal pulses can be applied to this pin.

Conclusion No. 7 - Discharge.

This pin is connected to the collector of transistor T1, the emitter of which is connected to the common wire. When the transistor is open, capacitor C is discharged through the collector-emitter junction and remains in a discharged state until the transistor closes. The transistor is closed when the timer output is high and open when the output is low.

Conclusion No. 8 - Nutrition.

The timer supply voltage ranges from 4.5 to 16 volts.

The timer can operate in two modes: monostable multivibrator and rectangular pulse generator.

1. Monostable multivibrator.

Monostable means that the timer has only one stable state, when it is turned off. It can be switched to the on state temporarily by applying some signal to the timer input. The time the timer is in active mode determined by RC circuit.

In the initial state, the output of the timer (pin No. 3) is low - approximately 0.25 volts, transistor T1 is open and, accordingly, the capacitor is discharged. This timer state is stable. When a low level pulse arrives at the input (pin No. 2), comparator No. 2 is turned on, which switches the timer trigger, and as a result, the timer output is set to a high level. Transistor T1 closes and capacitor C begins to charge through resistor R. And while capacitor C is charging, the output of the timer remains high. During this time, changes in the signal at the input (pin No. 2) will not cause any effect on the timer. After the voltage on capacitor C reaches 2/3 of the supply voltage, comparator No. 1 turns on and thereby switches the trigger. As a result, the output (pin No. 3) will go low, and the timer will restore its original, stable state. Transistor T1 will open and discharge capacitor C.

2. Rectangular pulse generator.

The timer generates a sequence of rectangular pulses determined by the RC chain.

In the initial state, capacitor C is discharged and the inputs of both comparators have a low level, close to zero. Comparator No. 2 switches the internal trigger and, as a result, the output of the timer (pin No. 3) is set to a high level. Transistor T1 closes and capacitor C begins to charge through the chain of resistors R1 and R2.

When, as a result of charging, the voltage on the capacitor reaches 2/3 of the supply voltage, comparator No. 1 switches the trigger, which in turn sets a low level at the output of the timer (pin No. 3). Transistor T1 opens and capacitor C begins to discharge through resistor R2. As soon as the voltage on the capacitor reaches 1/3 of the supply voltage, comparator No. 2 will switch the trigger again and a high level will again appear at the timer output (pin No. 3). Transistor T1 will close and capacitor C will begin to charge again.

The history of the creation of a very popular microcircuit and a description of its internal structure

One of the legends of electronics is NE555 integrated timer chip. It was developed back in 1972. Not every microcircuit or even every transistor can be proud of such longevity. So what is so special about this microcircuit that has three fives in its marking?

Signetics began serial production of the NE555 chip exactly one year after it was developed by Hans R. Camenzind. The most surprising thing in this story was that at that time Camenzind was practically unemployed: he quit the PR Mallory company, but did not manage to get a job anywhere. In essence, it was “homemade”.

The microcircuit saw the light of day and gained so much fame and popularity thanks to the efforts of Signetics manager Art Fury, who was, of course, Camenzind’s friend. He previously worked at General Electric, so he knew the electronics market, what was needed there, and how to attract the attention of a potential buyer.

According to Camenzind's recollections, A. Fury was a true enthusiast and lover of his work. At home he had a whole laboratory filled with radio components, where he conducted various studies and experiments. This made it possible to accumulate vast practical experience and deepen theoretical knowledge.

At that time, Signetics products were named “5**”, and the experienced A. Fury, who had an uncanny sense of the electronics market, decided that the marking 555 (three fives) would be just right for the new microcircuit. And he was not mistaken: the microcircuit went in great demand, it became, perhaps, the most widespread in the entire history of the creation of microcircuits. The most interesting thing is that the microcircuit has not lost its relevance to this day.

Somewhat later, two letters appeared in the marking of the microcircuit; it became known as NE555. But since at that time there was complete confusion in the patenting system, everyone rushed to produce the integral timer, naturally, putting other (read their) letters in front of the three fives. Later, based on the 555 timer, dual (IN556N) and quad (IN558N) timers were developed, naturally in more multi-pin packages. But the same NE555 was taken as the basis.

Rice. 1. NE555 integral timer

555 in the USSR

The first description of 555 in the domestic radio engineering literature appeared already in 1975 in the magazine “Electronics”. The authors of the article noted the fact that this microcircuit would be no less popular than the operational amplifiers that were already widely known at that time. And they weren't wrong at all. The microcircuit made it possible to create very simple designs, and almost all of them began to work immediately, without painful setup. But it is known that the repeatability of a design at home increases in proportion to the square of its “simplicity”.

In the Soviet Union, in the late 80s, a complete analogue of the 555 was developed, called KR1006VI1. The first industrial application of the domestic analogue was in the Elektronika VM12 video recorder.

Internal structure of the NE555 chip

Before you grab a soldering iron and start assembling the design on an integrated timer, let's first figure out what's inside and how it all works. After this, it will be much easier to understand how a specific practical scheme works.

Inside the integral timer there are over twenty, the connection of which is shown in the figure -

As you can see, the circuit diagram is quite complex, and is shown here for general information only. After all, you still can’t fit a soldering iron into it, and you won’t be able to repair it. As a matter of fact, this is exactly what all other microcircuits, both digital and analog, look like from the inside (see -). This is the production technology integrated circuits. It will also not be possible to understand the logic of operation of the device as a whole using such a scheme, so below is a functional diagram and its description.

Technical data

But, before you understand the logic of the microcircuit, you should probably give it electrical parameters. The supply voltage range is quite wide, 4.5…18V, and the output current can reach 200mA, which allows even low-power relays to be used as a load. The microcircuit itself consumes very little: only 3...6mA is added to the load current. At the same time, the accuracy of the timer itself practically does not depend on the supply voltage - only 1 percent of the calculated value. The drift is only 0.1%/volt. The temperature drift is also small - only 0.005%/°C. As you can see, everything is quite stable.

Functional diagram NE555 (KR1006VI1)

As mentioned above, in the USSR they made an analogue of the bourgeois NE555 and called it KR1006VI1. The analogue turned out to be very successful, no worse than the original, so you can use it without any fears or doubts. Figure 3 shows the functional diagram of the KR1006VI1 integrated timer. It is fully compatible with the NE555 chip.

Figure 3. Functional diagram of the integrated timer KR1006VI1

The chip itself is not that big - it is available in an eight-pin DIP8 package, as well as in a small-sized SOIC8. The latter suggests that 555 can be used for SMD mounting, in other words, developers are still interested in it.

There are also few elements inside the microcircuit. The main one is DD1. When a logical one is applied to the input R, the trigger is reset to zero, and when a logical one is applied to the input S, it is naturally set to one. To generate control signals at the RS inputs, it is used, which will be discussed a little later.

The physical levels of a logical unit depend, of course, on the supply voltage used and practically range from Upit/2 to almost full Upit. Approximately the same ratio is observed in CMOS logic chips. Logical zero is, as usual, within the range of 0...0.4V. But these levels are located inside the microcircuit, you can only guess about them, but you cannot touch them with your hands or see them with your eyes.

Output stage

To increase the load capacity of the microcircuit, a powerful output stage using transistors VT1, VT2 is connected to the trigger output.

If the RS trigger is reset, then a logical zero voltage is present at the output (pin 3), i.e. transistor VT2 is open. In the case when the trigger is set at the output, the level is also logical one.

The output stage is made according to a push-pull circuit, which allows you to connect a load between the output and the common wire (pins 3.1) or the power bus (pins 3.8).

A small note on the output stage. When repairing and setting up devices on digital microcircuits, one of the methods for checking the circuit is to apply a low-level signal to the inputs and outputs of the microcircuits. As a rule, this is done by shorting these same inputs and outputs to the common wire using a sewing needle, without causing any harm to the microcircuits.

In some circuits, the NE555 power supply is 5V, so it seems that this is also digital logic and can also be used quite freely. But actually it is not. In the case of the 555 microcircuit, more precisely with its push-pull output, such “experiments” cannot be done: if the output transistor VT1 is in the open state at this moment, then the result will be short circuit and the transistor will simply burn out. And if the supply voltage is close to the maximum, then a disastrous ending is simply inevitable.

Additional transistor (pin 7)

In addition to the mentioned transistors, there is also a VT3 transistor. The collector of this transistor is connected to pin 7 of microcircuit “Discharge”. Its purpose is to discharge the timing capacitor when using the microcircuit as a pulse generator. The capacitor discharge occurs at the moment the trigger DD1 is reset. If we recall the description of the trigger, then at the inverse output (indicated in the diagram by a circle) at this moment there is a logical unit, leading to the opening of transistor VT3.

About the reset signal (pin 4)

You can reset the trigger at any time - the “reset” signal has high priority. For this purpose, there is a special input R (pin 4), designated in the figure as Usbr. As you can understand from the figure, a reset will occur if a low-level pulse of no more than 0.7V is applied to pin 4. In this case, a low level voltage will appear at the output of the microcircuit (pin 3).

In cases where this input is not used, a logical one level is applied to it to get rid of impulse noise. The easiest way to do this is to connect pin 4 directly to the power bus. Under no circumstances should you leave it, so to speak, in the “air”. Then you will have to wonder and wonder for a long time, why does the scheme work so unstable?

Notes on the trigger "in general"

In order not to get completely confused about what state the trigger is in, it should be recalled that when discussing a trigger, the state of its direct output is always taken into account. Well, if it is said that the trigger is “installed,” then the direct output is in the state of logical one. If they say that the trigger is “reset,” the direct output will certainly be in a logical zero state.

At the inverse output (marked with a small circle), everything will be exactly the opposite, therefore, the trigger output is often called paraphase. In order not to confuse everything again, we will not talk about this anymore.

Anyone who has carefully read to this point may ask: “Excuse me, this is just a trigger with a powerful transistor stage at the output. Where is the timer itself?” And he will be right, since it hasn’t even come to the timer yet. To make a timer, his father, the creator Hans R. Camenzind, invented original way control this trigger. The whole trick of this method lies in the generation of control signals.

Generating signals at the RS trigger inputs

So, what did we get? The whole thing inside the timer is controlled by trigger DD1: if it is set to one, the output of the microcircuit has a high voltage level, and if it is reset, then pin 3 has a low level and, in addition, transistor VT3 is open. The purpose of this transistor is to discharge a timing capacitor in a circuit, for example, a pulse generator.

Trigger DD1 is controlled using comparators DA1 and DA2. In order to control the operation of the flip-flop, high-level R and S signals must be obtained at the outputs of the comparators. A reference voltage is supplied to one of the inputs of each comparator, which is formed by a precision divider on resistors R1…R3. The resistance of the resistors is the same, so the voltage applied to them is divided into 3 equal parts.

Generating Trigger Control Signals

Start a timer

A reference voltage of 1/3U is applied to the direct input of comparator DA2, and external voltage to start the timer Uzap through pin 2 is fed to the inverse input of the comparator. In order to influence the input S of flip-flop DD1, the output of this comparator must receive a high level. This is possible if the voltage Uzap is in the range of 0...1/3U.

Even a short-term pulse of such voltage will trigger trigger DD1 and cause a high voltage level to appear at the output of the timer. If the Uzap input is exposed to a voltage higher than 1/3U and up to the supply voltage, then no changes will occur at the output of the microcircuit.

Stop the timer

To stop the timer, you simply need to reset the internal trigger DD1, and to do this, generate a high-level R signal at the output of the comparator DA1. Comparator DA1 is switched on slightly differently than DA2. A reference voltage of 2/3U is applied to the inverting input, and the control signal “Operation threshold” Uthr is applied to the direct input.

With this connection, a high level at the output of comparator DA1 will occur only when the voltage Uthr at the direct input exceeds the reference voltage 2/3U at the inverting input. In this case, trigger DD1 will be reset, and a low level signal will be established at the output of the microcircuit (pin 3). The “discharge” transistor VT3 will also open, which will discharge the timing capacitor.

If the input voltage is within 1/3U...2/3U, none of the comparators will work, and the state at the timer output will not change. IN digital technology This voltage is called the “gray level”. If you simply connect pins 2 and 6, you get a comparator with trigger levels of 1/3U and 2/3U. And even without a single additional detail!

Changing reference voltage

Pin 5, designated in the figure as Urev, is intended for monitoring the reference voltage or changing it using additional resistors. It is also possible to supply a control voltage to this input, making it possible to obtain a frequency or phase modulated signal. But more often this pin is not used, but to reduce the influence of interference it is connected to the common wire through a small capacitor.

The microcircuit is powered through pins 1 - GND, 2 +U.

Here is the actual description of the NE555 integrated timer. The timer contains a lot of different circuits, which will be discussed in the following articles.

Boris Aladyshkin

Continuation of the article:

The 555 series chip was developed quite a long time ago, but still remains relevant. On the basis of a chip, several dozen of the most various devices With minimum quantity additional components in the circuit. The simplicity of calculating the values of components of the microcircuit body kit is also its important advantage.

This article will discuss two options for using a microcircuit in a time relay circuit with:

Turn-on delay;
Shutdown delay.

In both cases, the 555 chip will function as a timer.

How does the 555 chip work?

Before moving on to the example of a relay device, let's consider the structure of the microcircuit. All further descriptions will be made for the series microcircuit NE555 manufactured by Texas Instruments.

As can be seen from the figure, the basis is RS flip-flop with inverse output, controlled by outputs from comparators. The positive input of the upper comparator is called THRESHOLD, negative input of the lower - TRIGGER. Other comparator inputs are connected to a supply voltage divider consisting of three 5 kOhm resistors.

As you most likely know, an RS flip-flop can be in a steady state (it has a memory effect of 1 bit) either in a logical “0” or in a logical “1”. How it works:

R (RESET) sets the output to logical "1"(precisely “1”, not “0”, since the trigger is inverse - this is indicated by the circle at the output of the trigger);
Arrival of a positive impulse at the input S (SET) sets the output to logical "0".

Three 5 kOhm resistors divide the supply voltage by 3, which leads to the fact that the reference voltage of the upper comparator (the “–” input of the comparator, also known as the CONTROL VOLTAGE input of the microcircuit) is 2/3 Vcc. The lower reference voltage is 1/3 Vcc.

With this in mind, it is possible to create tables of states of the microcircuit relative to the inputs TRIGGER, THRESHOLD and exit OUT. Note that the OUT output is the inverted signal from the RS flip-flop.

Using this functionality of the microcircuit, you can easily make various signal generators with a generation frequency independent of the supply voltage.

In our case, to create a time relay, the following trick is used: the TRIGGER and THRESHOLD inputs are combined together and a signal is supplied to them from the RC chain. The state table in this case will look like this:

The NE555 connection diagram for this case is as follows:

After power is applied, the capacitor begins to charge, which leads to a gradual increase in the voltage across the capacitor from 0V onwards. In turn, the voltage at the TRIGGER and THRESHOLD inputs will, on the contrary, decrease, starting from Vcc+. As can be seen from the state table, there is a logical “0” at the OUT output after Vcc+ is applied, and the OUT output switches to a logical “1” when the voltage at the indicated TRIGGER and THRESHOLD inputs drops below 1/3 Vcc.

The important fact is that relay delay time, that is, the time interval between applying power and charging the capacitor until the OUT output switches to logical “1”, can be calculated using a very simple formula:

T = 1.1 * R * C
And as you can see, this time does not depend on the supply voltage. Consequently, when designing a time relay circuit, you don’t have to worry about power stability, which significantly simplifies the circuit design.

It is also worth mentioning that in addition to the 555 series, episode 556 in a 14-pin package. The 556 series contains two 555 timers.

Device with delay function

Let's move directly to the time relay. In this article we will analyze, on the one hand, a circuit that is as simple as possible, but on the other hand, it does not have galvanic isolation.

Attention! Assembly and adjustment of the circuit in question without galvanic isolation should be performed only by specialists with the appropriate education and approvals. The device is dangerous because it contains dangerous voltage.

Such a device in its design has 15 elements and is divided into two parts:

Supply voltage generation unit or power supply unit;
Node with temporary controller.

The power supply operates on a transformerless principle. Its design includes components R1, C1, VD1, VD2, C3 and VD3. The 12 V supply voltage itself is formed on the zener diode VD3 and smoothed by capacitor C3.

The second part of the circuit includes an integrated timer with a fitting. We described the role of capacitor C4 and resistor R2 above, and now, using the previously stated formula, we can calculate the value of the relay delay time:

T = 1.1 * R2 * C4 = 1.1 * 680000 * 0.0001 = 75 seconds ≈ 1.5 minutes By changing the values of R2-C4, you can independently determine the delay time you need and remake the circuit yourself for any time interval.

The operating principle of the circuit is as follows. After the device is connected to the network and the supply voltage appears on the zener diode VD3, and, consequently, on the NE555 chip, the capacitor begins to charge until the voltage at inputs 2 and 6 of the NE555 chip drops below 1/3 of the supply, that is, to approximately 4 V. After this event occurs, the OUT output will appear control voltage, which will start (turn on) relay K1. The relay, in turn, will close the load HL1.

Diode VD4 accelerates the discharge of capacitor C4 after a power failure so that after a quick restart connection to the device network, the response time has not been reduced. Diode VD5 dampens the inductive surge from K1, thereby protecting the circuit. C2 is used to filter interference from the NE555 power supply.

If the parts are selected correctly and the elements are installed without errors, then the device does not need to be configured.

When testing the circuit, in order not to wait a minute and a half, it is necessary to reduce the resistance R1 to a value of 68–100 kOhm.

You probably noticed that there is no transistor in the circuit that would turn on relay K1. This was done not out of economy, but because of the sufficient reliability of output 3 (OUT) of the DD1 chip. The NE555 chip supports the OUT output maximum load up to ±225 mA.

This scheme is ideal to control the operating time of ventilation devices installed in bathrooms and other utility rooms. Due to its presence fans turn on only if they are present in the room for a long time. This regime significantly reduces consumption electrical energy, and extends the service life of fans due to less wear of rubbing parts.

How to make a relay with a switch-off delay

The above circuit, thanks to the features of the NE555, can be easily converted into a shutdown delay timer. To do this, you need to swap C4 and R2-VD4. In this case, K1 will close the load HL1 immediately after turning on the device. The load will be turned off after the voltage on capacitor C4 increases to 2/3 of the supply voltage, that is, to approximately 8 V.

The disadvantage of this modification is the fact that after disconnecting the load, the circuit will remain exposed to dangerous voltage. This drawback can be eliminated by connecting a relay contact to the power supply circuit to the timer in parallel with the power button ( just a button, not a switch!).

The diagram of such a device, taking into account all the modifications, is shown below:

Attention! In order for dangerous voltage to actually be removed from the circuit by the relay contact, it is necessary that the PHASE be connected exactly as shown in the diagram.

Please note that the 555 timer is used and described on our website in another article in which it is discussed. The diagram presented there is more reliable, contains galvanic isolation and allows you to change the time interval using the regulator.

If you need a drawing when manufacturing a product printed circuit board, write about it in the comments.

Video on the topic

It is immediately worth noting when describing the NE 555 chip that it is produced in both standard TTL and CMOS logic, so it can operate in a wide range of voltages and is used in many types of devices as a clock generator or universal timer. The microcircuit can generate both single and repeating pulses, which depends on schematic diagram turning on and selecting a specific operating mode.

The first version of the IC was developed back in 1971 by the then famous company Signetics. According to its characteristics and functionality it is widely in demand, as evidenced by its active use in motor speed control devices and thyristor power regulators.

Also, it can be used to design a unified pulse generator with an adjustable output frequency by a pulse sequence. For detailed description microcircuit characteristics see ne 555 datasheet. It indicates not only the main characteristics, but also provides operation diagrams. And in this description we will provide ne 555 general information, sufficient for development electronic devices with your own hands.

Background to the creation of IP

In the 70s the Signetics company fell under the influence of the crisis and was forced to reduce the number of its staff by at least 50%, including the developer of the presented scheme. That's why she was created literally on his knees in a garage, and the NE 566 he developed was taken as a basis. The platform of the future IC already consisted of the basic functional blocks necessary for operation:

There are switching diagrams for the ne 555 different types For the microcircuit to operate, the presence of an external RC circuit, which was the timing circuit, was sufficient. And internal voltage divider, in proportion to which the amplitude of the output signal was formed. After some time and minor modifications, in particular, replacing the built-in stable current generator for charging the internal capacitor with a resistor, it entered production.

As for the timer structure, it contained:

23 transistors;
16 resistors;
2 diodes.

Microcircuit analogues

The universal timer soon acquired functional analogues, which were Soviet microcircuits from the KR series:

1006VI1;
1008VI1;
1087VI2;
1087VI3.

Also, the ne555 microcircuit has an analogue, for example, KR10006VI1, then it is worth considering the fact that the reset input R has priority in relation to the installation. This somehow the moment was missed V technical description MS, which is an important fact when constructing electronic circuits. In other microcircuits, pins have priority up to the opposite S over R.

All of the above analogues of timers are built on standard TTL logic. If you want to design devices based on ne555 with more economical performance, then it is better to use MS from the CMOS series. These are the devices:

ICM 7555 IPA;
GLC 555;
KR1441VI1.

Chip characteristics

The functional diagram of the presented microcircuit is quite simple and consists of the following blocks:

a voltage divider that compares the input signal to two reference levels;
2 high-precision comparators for high and low signal levels;
trigger with built-in RS inputs and additional reset, medium power output transistor is bipolar or field effect depending on the technology.

Also, the hardware design of the microcircuit provides a power amplifier, which increases the load capacity of the device and its quality of operation.

The microcircuit is universal, no matter how you look at it, from all sides. For example, basic version NE 555 is designed to supply voltage in the range from 4.5 to 16.5 V, which greatly simplifies the process of designing many circuits, since there is no need to adhere to a specific power supply.

But if it is necessary to power the pulse generator from a reduced level of the order of 2–3 V, then it is better to use circuits based on CMOS logic. Not only can they function freely at low voltage, but also have increased resistance to interference and power instability.

Also, modifications of devices are available with an increased supply voltage threshold, which can reach 18 V. These MS can be used in pulse devices and generators.

According to the information provided by the Western ne555 datasheet, the current consumed by the device depends on the size of the input pulse. If it lies at a nominal level of about 5 V, then current value is no more than 6 mA. But if the voltage rises to 15V, then the current also rises to 15mA. Typically, devices are developed by hand using average current, which leaves about 10 mA, which indicates a supply voltage ranging from 9 to 12 V. But this is typical for TTL logic.

Microcircuits designed on the basis of CMOS transistors consume even less - 100-200 μA, which makes them even more economical. But the maximum value of current consumption does not exceed 100 mA. If it takes more than this value from you, this means that the device is faulty and requires replacement.

Some problems and features of working with a microcircuit

The 8-pin case is a good idea, but this form factor causes some difficulties when working with the timer. Namely, it is deprived of the ability to independently compare the signals of the upper and lower thresholds, which quite often required in conversion devices, for example, the same ADCs. To realize this possibility, radio amateurs resort to using another series of devices, for example, NE 521, or install 3I-NOT elements at the input, if appropriate.

Bipolar devices have a drawback such as a pulse current when turning on and off, the value of which can reach 400 mA, which can cause breakdown output transistor or other elements of the circuit into which it was soldered. The reason for this phenomenon is the through current of the output stage, which arises due to the same high power supply pulses.

To fix the problem, it is recommended to use a special blocking capacitor connected to inputs 5 and common (minus power supply) with a capacity of about 0.01–0.1 μF. Due to the charge of its plates, the internal voltage in the MS, entering the output stage, is smoothed out, which eliminates the possibility of a breakdown. It will also protect the internal divider from external interference that could cause false triggering.

Also, as is the case with many other TTL logic microcircuits, it is recommended to bypass the NE 555 with a quenching capacitor with 1 µF ceramic plates.

Purpose and location of microcircuit pins

NE 555 in its basic version has an 8-pin DIP package, but other modifications that are analogous are also available. Therefore, orient only this description when building devices with your own hands based on it, it is not worth it. Each chip needs to view its own datasheet.

The schematic designation of the device is displayed as the inscription “G 1/ GN”. In foreign reference books, this inscription can be deciphered as a generator of single and series of pulses. What concerns the location of the terminals and their purposes, then all MSs of the same type are standardized and can be interchangeable without making any modifications.

The table below shows the pinout arrangement in a standard MS case:

Operating modes and application of the microcircuit

The simplest circuit implementation used in various digital devices, is a one-shot device. Using this circuit as an example, you can also see a typical connection using quenching and shunt capacitors. It is in this design that this microcircuit is most often used. And it works like this:

When a low-level signal arrives at the MS input number 2, the timer starts working in time counting mode. In this case, the output of the device is set to a high level throughout the entire duration of time period. You can set this time yourself by selecting the necessary external components, which are a resistor and a capacitor connected to the power plus and pin number 6.

The time delay is determined using the standard formula taking into account the correction constant: t =1.1 RC. At the end of the count (discharge of the capacitor), the timer returns to its original state. And the output signal changes to the opposite. So until the next arrival of the low level input pulse.

In this case, if there is a low level at the input, then the output is high. And when a pulse is applied to the reset input of the trigger, the timer stops counting and the output signal level changes to the opposite.

Independent generator mode

To enable the microcircuit in multivibrator mode, there is a circuit shown in the figure below. Everything here is as simple as in the previous version, but there are some features in the calculation of the element and the characteristics of the output signal sequence. To set a specific frequency changing the output signal and subsequent switching to the opposite stable state, you will need to combine pins 2 and 6 and install another resistor in divide, reducing the capacitor charge current, but at the same time connecting the input signal to the trigger setup input. And to calculate the parameters used by the element, you will need to use the following simple formulas calculation:

Changing the duty cycle of the output pulse

Often it is necessary to use a 555 microcircuit with the ability to set the duty cycle of the output signal. For example, to make it more than 2, then this will require forming an additional chain between 7 and 6 pins by connecting a diode to them. In this case, the anode terminal is in contact with terminal 7 of the MS. Such inclusion additional component shunts resistor R 2, providing a capacitor charging circuit through R 1. Then, when calculating the duration of a high signal level at the output, it will occur according to the formula without taking into account R 2.

In reverse cycle discharge current will flow through R 2, and R 1 is no longer involved in the process. And it is determined by the formula indicated above without changes.