Diode reverse current formula. Reverse voltage
U arr. m ax = 1.045U avg.
In a number of practical applications, thyristor converters are used to rectify alternating current and smoothly control the power transmitted to the load. At the same time, small control currents make it possible to control large load currents.
An example of the simplest power-controlled thyristor rectifier is shown in Fig. 7.10.
Rice. 7.10. Thyristor rectifier circuit
In Fig. Figure 7.11 shows timing diagrams that explain the principle of regulating the average value of the rectified voltage.
Rice. 7.11. Timing diagrams of thyristor rectifier operation
In this circuit, it is assumed that the input voltage Uin for an adjustable thyristor is generated, for example, by a full-wave rectifier. If control pulses U y of sufficient amplitude are supplied at the beginning of each half-cycle (section o-a in the U out diagram), the output voltage will repeat the voltage of the full-wave rectifier. If you shift the control pulses to the middle of each half-cycle, then the output pulses will have a duration equal to a quarter of the half-cycle (section b-c). Further displacement of the control pulses will lead to a further decrease in the average amplitude of the output pulses (section d – e).
Thus, by applying control pulses to the thyristor that are phase-shifted relative to the input voltage, you can turn a sinusoidal voltage (current) into a sequence of pulses of any duration, amplitude and polarity, that is, you can change the effective value of the voltage (current) within a wide range.
7.3 Anti-aliasing filters
The considered rectification circuits make it possible to obtain a unipolar pulsating voltage, which is not always applicable for powering complex electronic devices, since, due to large pulsations, they lead to instability of their operation.
To significantly reduce ripple, smoothing filters are used. The most important parameter of the smoothing filter is the smoothing coefficient S, determined by the formula S= 1 / 2, where 1 and 2 are the ripple coefficients at the input and output of the filter, respectively. The ripple factor shows how many times the filter reduces ripple. In practical circuits, the ripple factor at the filter output can reach values of 0.00003.
The main elements of filters are reactive elements - capacitance and inductance (chokes). Let us first consider the principle of operation of the simplest anti-aliasing filter, the diagram of which is shown in Fig. 7.12.
Rice. 7.12. Circuit of the simplest smoothing filter with a half-wave rectifier
In this circuit, smoothing of the voltage across the load after a half-wave diode rectifier VD is carried out using a capacitor C connected in parallel with the load R n.
Timing diagrams explaining the operation of such a filter are shown in Fig. 7.13. In the t1 – t2 section, the input voltage opens the diode and charges the capacitor. When the input voltage begins to decrease, the diode closes with the voltage accumulated on the capacitor U c (section t1 - t2). During this interval, the input voltage source is disconnected from the capacitor and the load, and the capacitor is discharged through the load resistance R n.
Rice. 7.13. Timing diagrams of filter operation with a half-wave rectifier
If the capacitance is large enough, the discharge of the capacitance through R n will occur with a large time constant = R n C, and therefore, the decrease in voltage on the capacitor will be small, and the smoothing effect will be significant. On the other hand, the larger the capacitance, the shorter the segment t1 - t2 during which the diode is open and current i flows through it, increasing (for a given average load current) as the difference t2 - t1 decreases. This mode of operation can lead to failure of the rectifier diode, and, in addition, is quite heavy for the transformer.
When using full-wave rectifiers, the amount of ripple at the output of the capacitive filter decreases, since the capacitor is smaller during the time between the appearance of pulses, which is well illustrated in Fig. 7.14.
Rice. 7.14. Full-Wave Rectifier Ripple Smoothing
To calculate the magnitude of ripple at the output of a capacitive filter, we will approximate the ripple of the output voltage using a sawtooth current curve, as shown in Fig. 7.15.
Rice. 7.15. Ripple voltage approximation
The change in charge on the capacitor is determined by the expression
∆Q=∆UC=I n T 1,
where T 1 is the pulsation period, I n is the average value of the load current. Taking into account the fact that I n = I av / R n, we obtain
.
From Fig. 7.15 it follows that
in this case, the double amplitude of the pulsations is determined by the expression
.
Inductive filters also have smoothing properties, and the best smoothing properties are found in filters containing inductance and capacitance connected as shown in Fig. 7.16.
Rice. 7.16. Anti-aliasing filter with inductance and capacitance
In this circuit, the capacitance of the capacitor is selected so that its reactance is significantly less than the load resistance. The advantage of such a filter is that it reduces the input ripple ∆U to the value 
, where ω is the pulsation frequency.
In practice, various types of F-shaped and U-shaped filters have become widespread, the construction options of which are presented in Fig. 7.17.
At low load currents, the F-shaped rectifier shown in Fig. works well. 7.16.
Rice. 7.17. Filter construction options
In the most critical schemes, multi-link filtering circuits are used (Fig. 7.17 d).
Often the inductor is replaced with resistors, which somewhat reduces the quality of filtration, but significantly reduces the cost of filters (Fig. 7.17 b, c).
The main external characteristic of rectifiers with a filter is the dependence of the average value of the output voltage U cf (load voltage) on the average value of the output current.
In the considered circuits, an increase in the output current leads to a decrease in U av due to an increase in the voltage drop across the transformer windings, diodes, lead wires, and filter elements.
The slope of the external characteristic at a given average current is determined through the output resistance Rout, determined by the formula:
I cf – specified. The smaller the value of Rout, the less the output voltage depends on the output current, the better the rectifier circuit with a filter. In Fig. Figure 7.18 shows typical dependences of Uav on Iav for various filtration options.
Rice. 7.18. Typical dependences of Uav on Iav for various filtration schemes
Published Date: 12/23/2017
Do you know what reverse voltage is?
Reverse voltage
Reverse voltage is a type of energy signal created when the polarity of an electrical current is reversed. This voltage often occurs when reverse polarity is applied to a diode, causing the diode to react by operating in the opposite direction. This reverse function can also create a breakdown voltage within the diode, as this often breaks the circuit to which the voltage is applied.
Reverse voltage occurs when the power signal connection source to a circuit is applied in an inverted manner. This means that the positive lead source is connected to the ground or negative conductor of the circuit and vice versa. This voltage transfer is often not intended, as most electrical circuits are not capable of handling voltages.
When minimum voltage is applied to a circuit or diode, it may cause the circuit or diode to operate in reverse. This may cause a reaction such as the box fan motor turning incorrectly. The element will continue to function in such cases.
When the amount of voltage applied to a circuit is too large, the signal for the receiving circuit, however, is called breakdown voltage. If the input signal that has been reversed exceeds the allowable voltage for the circuit to maintain, the circuit may be damaged beyond the rest of the usable. The point at which the circuit is damaged refers to the breakdown voltage value. This breakdown voltage has a couple of other names, reverse peak voltage or reverse breakdown voltage.
Reverse voltage can cause breakdown voltage, which also affects the operation of other circuit components. Beyond the damaging diodes and reverse voltage circuit functions, it can also become a reverse voltage peak. In such cases, the circuit cannot contain the amount of input power from the signal that has been reversed, and may create a breakdown voltage between the insulators.
This breakdown voltage, which can occur across circuit components, can cause breakdown of components or wire insulators. This can turn them into signal conductors and damage the circuit by conducting voltage to different parts of the circuit that should not receive it, causing instability throughout the circuit. This can cause voltage arcs from component to component, which can also be powerful enough to ignite various circuit components and cause a fire.
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During the life cycle of a building, renovation work is necessary at certain periods to update the interior. Modernization is also necessary when interior design or functionality lags behind modern times.
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There are more than 100 million housing units in Russia, and most of them are “single-family houses” or cottages. In cities, suburbs and rural areas, own homes are a very common type of housing.
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1. The real estate developer who provides financing for the project;
One or more financial institutions or other investors that provide financing;
2. Local planning and management bodies;
3. Service that carries out ALTA/ACSM and construction surveys throughout the project;
4. Building managers who coordinate the efforts of various groups of project participants;
5. Licensed architects and engineers who design buildings and prepare construction documents;
The simplest design in the family of semiconductors are diodes, which have only two electrodes between which there is conductivity of electric current in one direction. This type of conductivity in semiconductors is created due to their internal structure.
Device Features
Without knowing the design features of the diode, it is impossible to understand its operating principle. The diode structure consists of two layers with different types of conductivity.
The diode consists of the following main elements:
- Frame. It is made in the form of a vacuum cylinder, the material of which can be ceramics, metal, glass and other durable materials.
- Cathode. It is located inside the balloon and serves to generate electron emission. The simplest cathode device is a thin thread that glows during operation. Modern diodes are equipped with indirectly heated electrodes, which are made in the form of metal cylinders with the property of an active layer that has the ability to emit electrons.
- Heater. This is a special element in the form of a thread that is heated by electric current. The heater is located inside an indirectly heated cathode.
- Anode. This is the second electrode of the diode, which serves to receive electrons emitted from the cathode. The anode has a positive potential compared to the cathode. The shape of the anode is most often the same as the cathode, cylindrical. Both electrodes are similar to the emitter and base of semiconductors.
- Crystal. Its material of manufacture is germanium or silicon. One part of the crystal is p-type with a lack of electrons. The other part of the crystal has n-type conductivity with an excess of electrons. The boundary located between these two parts of the crystal is called a p-n junction.
These design features of the diode allow it to conduct current in one direction.
Operating principle
The operation of a diode is characterized by its various states, and the properties of the semiconductor when in these states. Let's take a closer look at the main types of diode connections and what processes occur inside the semiconductor.
Diodes at rest
If the diode is not connected to the circuit, then peculiar processes still occur inside it. There is an excess of electrons in the "n" region, which creates a negative potential. The positive charge is concentrated in the “p” region. Together, such charges create an electric field.
Since charges with opposite signs attract, electrons from “n” pass into “p”, filling the holes. As a result of such processes, a very weak current appears in the semiconductor, and the density of the substance in the “p” region increases to a certain value. In this case, the particles disperse uniformly throughout the volume of space, that is, slow diffusion occurs. As a result, the electrons return to the “n” region.
For many electrical devices, the direction of the current does not really matter; everything works fine. For a diode, the direction of current flow is of great importance. The main task of a diode is to pass current in one direction, which is facilitated by the p-n junction.
Reverse switching
If the diodes are connected to the power supply according to the diagram shown, then the current will not pass through the p-n junction. The positive pole of the power supply is connected to the “n” area, and the negative pole is connected to “p”. As a result, electrons from the “n” region move to the positive pole of the power supply. Holes are attracted by the negative pole. A void appears at the transition; there are no charge carriers.
As the voltage increases, holes and electrons attract more strongly, and there are no charge carriers at the junction. When the diode is turned on in reverse, no current flows.
An increase in the density of matter near the poles creates diffusion, that is, the tendency to distribute matter throughout the volume. This occurs when the power is turned off.
Reverse current
Let us recall the work of minority charge carriers. When the diode is turned off, a small amount of reverse current passes through it. It is formed from minority carriers moving in the opposite direction. This movement occurs when the power supply polarity is reversed. The reverse current is usually negligible because the number of minority carriers is very small.
As the temperature of the crystal increases, their number increases and causes an increase in the reverse current, which usually leads to damage to the junction. In order to limit the operating temperature of semiconductors, their housing is mounted on heat-removing cooling radiators.
Direct connection
Let's swap the power poles between the cathode and anode. On the "n" side, electrons will move away from the negative terminal and flow towards the junction. On the “p” side, holes that have a positive charge will be pushed away from the positive power terminal. Therefore, electrons and holes will begin to rapidly move towards each other.
Particles with different charges accumulate near the junction, and an electric field is formed between them. Electrons pass through the p-n junction and move to the “p” region. Some electrons recombine with holes, and the rest pass to the positive pole of the power supply. A forward diode current arises, which is limited by its properties. If this value is exceeded, the diode may fail.
In the direct circuit of the diode, its resistance is insignificant, in contrast to the reverse circuit. It is believed that current does not flow back through the diode. As a result, we found out that diodes operate on the principle of a valve: turn the knob to the left - water flows, to the right - no water. Therefore, they are also called semiconductor valves.
Forward and reverse voltage
When the diode opens, there is forward voltage across it. Reverse voltage is the value when the diode closes and reverse current passes through it. The diode resistance at forward voltage is very small, in contrast to reverse voltage, which increases to thousands of kOhms. This can be verified by measuring with a multimeter.
The resistance of a semiconductor crystal can vary depending on the voltage. As this value increases, the resistance decreases, and vice versa.
If diodes are used in operation with alternating current, then with a positive half-wave of the sine voltage it will be open, and with a negative half-wave it will be closed. This property of diodes is used to rectify voltage. Therefore, such devices are called rectifiers.
Diode characteristics
The characteristics of the diode are expressed by a graph that shows the dependence of current, voltage and its polarity. The vertical coordinate axis in the upper part determines the forward current, in the lower part - the reverse one.
The horizontal axis on the right indicates forward voltage, and the horizontal axis on the left indicates reverse voltage. The straight branch of the graph expresses the diode's passing current and runs close to the vertical axis, as it expresses an increase in the forward current.
The second branch of the graph shows the current when the diode is closed, and runs parallel to the horizontal axis. The steeper the graph, the better the diode rectifies current. As the forward voltage increases, the current slowly increases. Having reached the jump region, its magnitude increases sharply.
The reverse branch of the graph shows that as the reverse voltage increases, the current practically does not increase. But, when the permissible limits are reached, a sharp jump in the reverse current occurs. As a result, the diode will overheat and fail.
Published Date: 12/23/2017
Do you know what reverse voltage is?
Reverse voltage
Reverse voltage is a type of energy signal created when the polarity of an electrical current is reversed. This voltage often occurs when reverse polarity is applied to a diode, causing the diode to react by operating in the opposite direction. This reverse function can also create a breakdown voltage within the diode, as this often breaks the circuit to which the voltage is applied.
Reverse voltage occurs when the power signal connection source to a circuit is applied in an inverted manner. This means that the positive lead source is connected to the ground or negative conductor of the circuit and vice versa. This voltage transfer is often not intended, as most electrical circuits are not capable of handling voltages.
When minimum voltage is applied to a circuit or diode, it may cause the circuit or diode to operate in reverse. This may cause a reaction such as the box fan motor turning incorrectly. The element will continue to function in such cases.
When the amount of voltage applied to a circuit is too large, the signal for the receiving circuit, however, is called breakdown voltage. If the input signal that has been reversed exceeds the allowable voltage for the circuit to maintain, the circuit may be damaged beyond the rest of the usable. The point at which the circuit is damaged refers to the breakdown voltage value. This breakdown voltage has a couple of other names, reverse peak voltage or reverse breakdown voltage.
Reverse voltage can cause breakdown voltage, which also affects the operation of other circuit components. Beyond the damaging diodes and reverse voltage circuit functions, it can also become a reverse voltage peak. In such cases, the circuit cannot contain the amount of input power from the signal that has been reversed, and may create a breakdown voltage between the insulators.
This breakdown voltage, which can occur across circuit components, can cause breakdown of components or wire insulators. This can turn them into signal conductors and damage the circuit by conducting voltage to different parts of the circuit that should not receive it, causing instability throughout the circuit. This can cause voltage arcs from component to component, which can also be powerful enough to ignite various circuit components and cause a fire.
Post navigation
Healthy
Renovation interior construction
During the life cycle of a building, renovation work is necessary at certain periods to update the interior. Modernization is also necessary when interior design or functionality lags behind modern times.
Multi-storey construction
There are more than 100 million housing units in Russia, and most of them are “single-family houses” or cottages. In cities, suburbs and rural areas, own homes are a very common type of housing.
The practice of designing, constructing and operating buildings is most often a collective effort among various groups of professionals and professions. Depending on the size, complexity and purpose of a particular building project, the project team may include:
1. The real estate developer who provides financing for the project;
One or more financial institutions or other investors that provide financing;
2. Local planning and management bodies;
3. Service that carries out ALTA/ACSM and construction surveys throughout the project;
4. Building managers who coordinate the efforts of various groups of project participants;
5. Licensed architects and engineers who design buildings and prepare construction documents;
What is forward and reverse voltage? I'm trying to understand the principle of operation of a field-effect transistor. and got the best answer
Answer from Vovik[active]
Direct - a plus is applied to a plus, a minus is applied to a minus. The opposite is true - to a plus - a minus, to a minus - a plus.
In relation to a field-effect transistor - between the source and the gate.
A bipolar transistor has a base and an emitter, not a field effect transistor.
A bipolar transistor consists of two back-to-back pn junctions with one common output - emitter - base (common type) - collector, like two diodes, only the common “layer” is thin and conducts current if a direct voltage, called opening, is applied between emitter and base.
The greater the forward voltage between the base and emitter, the more open the transistor is and the lower its emitter-collector resistance, i.e., there is an inverse relationship between the emitter-base voltage and the resistance of the bipolar transistor.
If a reverse voltage is applied between the base and emitter, the transistor will turn off completely and will not conduct current.
If you apply voltage only to the base and emitter or base and collector, you get a regular diode.
The field-effect transistor is designed somewhat differently. There are also three terminals, but they are called drain, source and gate. There is only one pn junction, gate -> drain-source or gate<- сток-исток в зависимости от полярности транзистора. Затвор находится между истоком и стоком и к нему (измеряется относительно истока) всегда прикладывается только обратное напряжение, которое создаёт поле в промежутке между истоком и стоком, в зависимости от напряжённости больше или меньше препятствующее движению электронов (следовательно, изменяя сопротивление транзистора) , и, таким образом, создающую обратную зависимость между напряжением исток-затвор и сопротивлением полевого транзистора.
Answer from ALEX R[guru]
On the 1st question, direct and reverse direc- tion occurs in a semiconductor (diode), i.e., the diode passes current in the direct direction, but if the current flows in the opposite direction, everything is closed. For clarity, the nipple of a bicycle tire goes there, there is no way back. Field tr-r, just for the sake of understanding, there is no electronic connection between the gate and the drain-source, but the current passes due to the evil field created at the gate. Something like that.
Answer from Alexander Egorov[guru]
direct - minus to the region with n-conductivity, plus to the region k with p-conductivity
the opposite is the opposite
by supplying only the emitter and collector, no current will pass, since the ionized atoms of the base will repel the free charges of the emitter from the pn junction (which are already difficult to jump over the pn junction, since it is a dielectric). And if you apply voltage to the base, it will “suck” free charges from the base and they will no longer repel the emitter charges, preventing them from crossing the pn junction. The transistor will open.
By the way, the emitter, collector and base are not a field-effect transistor, but a bipolar transistor.
If you apply voltage only to the base and emitter or base and collector, then it will be a simple diode (each pn junction is a diode).
Answer from User user[guru]
The field-effect transistor has a p or n type field-controlled channel. transistor terminals gate drain source