How does a thyristor work? Thyristor control, principle of operation The principle of operation of a thyristor in simple language

The operating principle of a thyristor

Thyristor is a power electronic not fully controlled key. Therefore, sometimes in the technical literature it is called a single-operation thyristor, which can only be switched into a conducting state by a control signal, i.e., turned on. To turn it off (when operating on direct current), it is necessary to take special measures to ensure that the forward current drops to zero.

A thyristor switch can only conduct current in one direction, and in the closed state it can withstand both forward and reverse voltage.

The thyristor has a four-layer p-n-p-n structure with three terminals: anode (A), cathode (C) and control electrode (G), as shown in Fig. 1

Rice. 1. Conventional thyristor: a) – graphical designation; b) – current-voltage characteristic.

In Fig. Figure 1b shows a family of output static current-voltage characteristics at various values ​​of the control current iG. The maximum forward voltage that the thyristor can withstand without turning it on has maximum values ​​at iG = 0. As the current iG increases, the forward voltage that the thyristor can withstand decreases. The on state of the thyristor corresponds to branch II, the off state corresponds to branch I, and the switching process corresponds to branch III. The holding current or holding current is equal to the minimum permissible value of the forward current iA at which the thyristor remains in a conducting state. This value also corresponds to the minimum possible value of the forward voltage drop across the switched on thyristor.

Branch IV represents the dependence of the leakage current on the reverse voltage. When the reverse voltage exceeds the UBO value, a sharp increase begins reverse current, associated with the breakdown of the thyristor. The nature of the breakdown may correspond to an irreversible process or an avalanche breakdown process characteristic of the operation of a semiconductor zener diode.

Thyristors are the most powerful electronic switches, capable of switching circuits with voltages up to 5 kV and currents up to 5 kA at a frequency of no more than 1 kHz.

The design of thyristors is shown in Fig. 2.

Rice. 2. Design of thyristor housings: a) – tablet type; b) – pin

Thyristor in a circuit DC

A conventional thyristor is turned on by supplying a current pulse to the control circuit with positive polarity relative to the cathode. The duration of the transient process when turned on is significantly influenced by the nature of the load (active, inductive, etc.), the amplitude and rate of rise of the control current pulse iG, the temperature of the semiconductor structure of the thyristor, the applied voltage and load current. In a circuit containing a thyristor, unacceptable values ​​of the forward voltage rise rate duAC/dt should not occur, at which spontaneous switching on of the thyristor may occur in the absence of a control signal iG and a current rise rate diA/dt. At the same time, the slope of the control signal must be high.

Among the methods of switching off thyristors, it is customary to distinguish between natural switching off (or natural switching) and forced switching (or artificial switching). Natural commutation occurs when thyristors operate in circuits AC at the moment the current drops to zero.

Methods of forced switching are very diverse. The most typical of them are the following: connecting a pre-charged capacitor with key S (Figure 3, a); connecting an LC circuit with a pre-charged capacitor CK (Figure 3 b); use of the oscillatory nature of the transient process in the load circuit (Figure 3, c).

Rice. 3. Methods of artificial switching of thyristors: a) – through a charged capacitor C; b) – through an oscillatory discharge of the LC circuit; c) – due to the oscillatory nature of the load

When switching according to the diagram in Fig. 3, and connecting a switching capacitor with reverse polarity, for example, with another auxiliary thyristor, will cause it to discharge to the conducting main thyristor. Because discharge current The capacitor is directed counter to the forward current of the thyristor, the latter decreases to zero and the thyristor turns off.

In the diagram in Fig. 3b, the connection of the LC circuit causes an oscillatory discharge of the switching capacitor Sk. In this case, at the beginning, the discharge current flows through the thyristor opposite to its forward current, when they become equal, the thyristor turns off. Next, the LC circuit current passes from the thyristor VS to the diode VD. As long as loop current flows through the diode VD, a reverse voltage will be applied to the thyristor VS equal to the voltage drop across the on-diode.

In the diagram in Fig. 3, turning on the VS thyristor to a complex RLC load will cause transition process. Under certain load parameters, this process can have an oscillatory nature with a change in the polarity of the load current in. In this case, after turning off the thyristor VS, the diode VD turns on, which begins to conduct current of the opposite polarity. Sometimes this switching method is called quasi-natural, since it is associated with a change in the polarity of the load current.

Thyristor in AC circuit

When a thyristor is connected to an alternating current circuit, the following operations can be performed:

Switching on and off an electrical circuit with an active and active-reactive load;

change in the average and effective values ​​of the current through the load due to the fact that it is possible to regulate the moment of supply of the control signal.

Since the thyristor switch is capable of conducting electric current only in one direction, then to use thyristors on alternating current, their back-to-back connection is used (Fig. 4,a).

Rice. 4. Back-to-back connection of thyristors (a) and current shape with an active load (b)

Average and vary due to changes in the moment of supply of opening signals to thyristors VS1 and VS2, i.e. due to changing the angle and (Fig. 4, b). The values ​​of this angle for thyristors VS1 and VS2 during regulation change simultaneously using the control system. The angle is called the control angle or the firing angle of the thyristor.

The most widely used in power electronic devices are phase (Fig. 4, a, b) and pulse-width control of thyristors(Fig. 4, c).

Rice. 5. Type of voltage on the load with: a) – phase control of the thyristor; b) – phase control of a thyristor with forced commutation; c) – pulse-width control of a thyristor

With the phase method of controlling a thyristor with forced commutation Load current regulation is possible by changing the angle? , and the angle? . Artificial switching is carried out using special units or using fully controlled (lockable) thyristors.

With pulse width control ( pulse width modulation– PWM) During the time Totkr, a control signal is applied to the thyristors, they are open and voltage Un is applied to the load. During the time Tclose there is no control signal and the thyristors are in a non-conducting state. Effective current value in the load

where In.m. – load current at Tclosed = 0.

The current curve in the load during phase control of thyristors is non-sinusoidal, which causes distortion of the supply voltage waveform and disturbances in the operation of consumers sensitive to high-frequency interference - so-called electromagnetic incompatibility occurs.

Lockable thyristors

Thyristors are the most powerful electronic switches used for switching high-voltage and high-current (high current) circuits. However, they have a significant drawback - incomplete controllability, which manifests itself in the fact that to turn them off it is necessary to create conditions for reducing the forward current to zero. This in many cases limits and complicates the use of thyristors.

To eliminate this drawback, thyristors have been developed that are gated by a signal via the control electrode G. Such thyristors are called gated (GTO - Gate turn-off thyristor) or two-operational.

Lockable thyristors(ZT) have a four-layer p-p-p-p structure, but at the same time have a number of significant design features, giving them a property fundamentally different from traditional thyristors full controllability. The static current-voltage characteristic of switched-off thyristors in the forward direction is identical to the current-voltage characteristic of conventional thyristors. However, a turn-off thyristor is usually not capable of blocking large reverse voltages and is often connected to a back-to-back diode. In addition, turn-off thyristors are characterized by significant forward voltage drops. To turn off a switchable thyristor, it is necessary to apply a powerful negative current pulse (approximately 1:5 relative to the value of the direct switched-off current), but of short duration (10-100 μs), into the control electrode circuit.

Turn-off thyristors also have lower voltage and current limits (by about 20-30%) compared to conventional thyristors.

Main types of thyristors

In addition to turn-off thyristors a wide range of thyristors has been developed various types, differing in speed, control processes, direction of currents in the conducting state etc. Among them, the following types should be noted:

thyristor-diode, which is equivalent to a thyristor with an anti-parallel connected diode (Fig. 6.12,a);

diode thyristor (dinistor), transforming into a conducting state when a certain voltage level applied between A and C is exceeded (Fig. 6,b);

turn-off thyristor(Fig. 6.12,c);

symmetrical thyristor or triac, which is equivalent to two back-to-back thyristors (Fig. 6.12,d);

fast acting inverter thyristor(turn-off time 5-50 µs);

thyristor with field control by control electrode, for example, based on a combination of a MOS transistor with a thyristor;

Optothyristor controlled by light flux.

Rice. 6. Graphic designation of thyristors: a) – thyristor-diode; b) – diode thyristor (dinistor); c) – turn-off thyristor; d) - triac

Thyristor protection

Thyristors are devices critical to the rate of rise of forward current diA/dt and forward voltage duAC/dt. Thyristors, like diodes, are characterized by the flow of reverse recovery current, a sharp drop of which to zero aggravates the possibility of overvoltages with high value duAC/dt. Such overvoltages are a consequence of a sudden cessation of current in the inductive elements of the circuit, including installation. Therefore, to protect thyristors they usually use various schemes CFTPs, which in dynamic modes protect against unacceptable values ​​of diA/dt and duAC/dt.

In most cases, the internal inductive reactance of the voltage sources included in the circuit of the switched-on thyristor turns out to be sufficient so as not to introduce additional inductance LS. Therefore, in practice, there is often a need for CFTPs that reduce the level and speed of overvoltages during shutdown (Fig. 7).

Rice. 7. Typical scheme thyristor protection

For this purpose, RC circuits connected in parallel with the thyristor are usually used. There are various circuit modifications of RC circuits and methods for calculating their parameters for different conditions of using thyristors.

For turn-off thyristors, switching trajectory formation circuits are used, similar in circuit design to CFTP transistors.

To understand how the circuit works, you need to know the action and purpose of each of the elements. In this article we will look at the operating principle of a thyristor, different types and operating modes, characteristics and types. We will try to explain everything as clearly as possible, so that it is clear even for beginners.

Thyristor - semiconductor element, having only two states: “open” (current flows) and “closed” (no current). Moreover, both states are stable, that is, the transition occurs only under certain conditions. The switching itself occurs very quickly, although not instantly.

In terms of its mode of action, it can be compared to a switch or a key. But the thyristor switches using voltage, and turns off when the current is lost or the load is removed. So the operating principle of a thyristor is not difficult to understand. You can think of it as an electrically controlled key. Well, not really.

A thyristor usually has three outputs. One control and two through which current flows. You can try to briefly describe the principle of operation. When voltage is applied to the control output, the circuit is switched through the anode-collector. That is, it is comparable to a transistor. The only difference is that in a transistor, the amount of current passed depends on the voltage applied to the control terminal. And the thyristor is either completely open or completely closed.

Appearance

The appearance of the thyristor depends on the date of its production. The elements from the times of the Soviet Union are metal, in the form of a “flying saucer” with three terminals. Two terminals - the cathode and the control electrode - are located on the “bottom” or “cover” (whichever side you look at). Moreover, the control electrode is smaller in size. The anode may be located on the opposite side of the cathode, or stick out to the side from under the washer that is on the body.

Two types of thyristors - modern and Soviet, designation on diagrams

Modern thyristors look different. This is a small plastic rectangle with a metal plate on top and three pins on the bottom. In the modern version there is one inconvenience: you need to look in the description which of the terminals is the anode, where is the cathode and the control electrode. Typically, the first is the anode, then the cathode and the one on the far right is the electrode. But this is usually the case, that is, not always.

Operating principle

According to the principle of operation, a thyristor can also be compared to a diode. It will pass current in one direction - from the anode to the cathode, but this will only happen in the “open” state. In the diagrams, a thyristor looks like a diode. There is also an anode and a cathode, but there is also an additional element - a control electrode. Of course, there are differences in the output voltage (when compared with a diode).

In alternating voltage circuits, the thyristor will pass only one half-wave - the upper one. When the lower half-wave arrives, it resets to the “closed” state.

The operating principle of a thyristor in simple words

Let's consider the principle of operation of a thyristor. The starting state of the element is closed. The “signal” to transition to the “open” state is the appearance of voltage between the anode and the control terminal. There are two ways to return the thyristor to the “closed” state:

• remove the load;
• reduce the current below the holding current (one of the technical characteristics).

In schemes with alternating voltage, as a rule, the thyristor is reset according to the second option. AC current household network has a sinusoidal shape when its value approaches zero and resets. In circuits powered by DC sources, it is necessary to either forcibly remove the power or remove the load.

That is, the thyristor works differently in circuits with constant and alternating voltage. In the diagram DC voltage, after a short-term appearance of voltage between the anode and the control terminal, the element goes into the “open” state. Then there can be two scenarios:

• The “open” state is maintained even after the anode-control output voltage has disappeared. This is possible if the voltage applied to the anode control terminal is higher than the non-unlocking voltage (this data is in the technical specifications). The flow of current through the thyristor is stopped, in fact only by breaking the circuit or turning off the power source. Moreover, the shutdown/break of the circuit can be very short-lived. After the circuit is restored, no current flows until voltage is applied to the anode control terminal again.
• After removing the voltage (it is less than the unlocking voltage), the thyristor immediately goes into the “closed” state.

So in DC circuits there are two options for using a thyristor - with and without holding the open state. But more often they use the first type - when it remains open.

The operating principle of a thyristor in alternating voltage circuits is different. There, the return to the locked state occurs “automatically” - when the current drops below the holding threshold. If the voltage is constantly applied to the anode-cathode, at the output of the thyristor we obtain current pulses that occur at a certain frequency. This is exactly how they are built impulse blocks nutrition. Using a thyristor, they convert the sine wave into pulses.

Functionality check

You can check the thyristor either using a multimeter or by creating a simple test circuit. If you have before your eyes when calling technical specifications, you can also check the resistance of the transitions.

Testing with a multimeter

First, let's analyze the continuity test with a multimeter. We switch the device to dialing mode.

Please note that the resistance value is different for different series - you should not pay attention to this special attention. If you want to check the resistance of the transitions, look at the technical specifications.

The figure shows the test diagrams. The figure on the far right is an improved version with a button that is installed between the cathode and the control terminal. In order for the multimeter to record the current flowing through the circuit, briefly press the button.

Using a light bulb and a DC source (a battery will also work)

If you don’t have a multimeter, you can test the thyristor using a light bulb and a power source. Even a regular battery or any other constant voltage source will do. But the voltage must be sufficient to light the light bulb. You will also need resistance or a regular piece of wire. A simple circuit is assembled from these elements:

• The plus from the power source is supplied to the anode.
• We connect a light bulb to the cathode, and connect its second terminal to the negative of the power source. The light does not light because the thermistor is locked.
• Briefly (using a piece of wire or resistance) connect the anode and the control terminal.
• The light comes on and continues to light even though the jumper is removed. The thermistor remains open.
• If you unscrew the light bulb or turn off the power source, the light bulb will naturally go out.
• If the circuit/power is restored, it will not light up.

Along with the test, this circuit allows you to understand the principle of operation of the thyristor. After all, the picture turns out to be very clear and understandable.

Types of thyristors and their special properties

Semiconductor technologies are still being developed and improved. Over several decades, new types of thyristors have appeared, which have some differences.

• Dinistors or diode thyristors. They differ in that they have only two outputs. Opened by feeding to the anode and cathode high voltage in the form of an impulse. They are also called “uncontrolled thyristors”.
• SCRs or triode thyristors. They have a control electrode, but the control pulse can be supplied:
  • To the control output and cathode. Name - with cathode control.
  • To the control electrode and anode. Accordingly, control of the anode.

There are also different types of thyristors according to the locking method. In one case, it is sufficient to reduce the anode current below the holding current level. In another case, a blocking voltage is applied to the control electrode.

By conductivity

We said that thyristors conduct current only in one direction. There is no reverse conduction. Such elements are called reverse-non-conducting, but there are not only such elements. There are other options:

• They have a low reverse voltage and are called reverse-conducting.
• With non-standardized reverse conductivity. They are installed in circuits where reverse voltage cannot occur.
• Triacs. Symmetrical thyristors. Conduct current in both directions.

Thyristors can operate in switch mode. That is, when a control pulse arrives, supply current to the load. The load, in this case, is calculated based on the open voltage. The maximum power dissipation must also be taken into account. In this case, it is better to choose metal models in the form of a “flying saucer”. It is convenient to attach a radiator to them for faster cooling.

Classification by special operating modes

The following subtypes of thyristors can also be distinguished:

• Lockable and non-lockable. The operating principle of an unlockable thyristor is slightly different. It is in the open state when the plus is applied to the anode, the minus is on the cathode. It goes into a closed state when the polarity changes.
• Fast-acting. They have a short transition time from one state to another.
• Pulse. It transitions very quickly from one state to another, and is used in circuits with pulsed operating modes.

The main purpose is to turn on and off powerful load using low-power control signals

The main area of ​​use of thyristors is as an electronic key used to close and open an electrical circuit. In general, many common devices are built on thyristors. For example, a garland with running lights, straighteners, pulsed sources current, rectifiers and many others.

Characteristics and their meaning

Some thyristors can switch very high currents, in which case they are called power thyristors. They are manufactured in metal case- for better heat dissipation. Small models with a plastic body are usually low-power options that are used in low-current circuits. But, there are always exceptions. So for each specific purpose, the required option is selected. They select, of course, according to parameters. Here are the main ones:

There is also a dynamic parameter - the time of transition from a closed to an open state. In some schemes this is important. The type of speed may also be indicated: by unlocking time or by locking time.

1.1 Definition, types of thyristors

1.2 Operating principle

1.3 Thyristor parameters

Chapter 2. Application of thyristors in power regulators

2.1 General information about various regulators

2.2 The process of voltage control using a thyristor

2.3 Controlled thyristor rectifier

Chapter 3. Practical development of power regulators based on thyristors

3.1 Voltage regulator on the KU201K thyristor

3.2 Powerful controlled rectifier using thyristors

Conclusion

Literature

Introduction

This paper examines several variants of devices that use thyristor elements as voltage regulators and as rectifiers. Theoretical and practical descriptions of the operating principle of thyristors and devices, as well as diagrams of these devices, are given.

A controlled rectifier based on thyristors - elements with a high power gain - makes it possible to obtain large currents in the load with little power spent in the thyristor control circuit.

This paper discusses two options for such rectifiers, which provide a maximum load current of up to 6 A with a voltage regulation limit from 0 to 15 V and from 0.5 to 15 V, and a device for adjusting the voltage on active and inductive loads powered from the network AC voltage 127 and 220 V with adjustment limits from 0 to rated network voltage.

Chapter 1. The concept of a thyristor. Types of thyristors. Operating principle

1.1 Definition, types of thyristors

A thyristor is a semiconductor device based on a four-layer structure that can switch from a closed state to an open state and vice versa. Thyristors are designed for key control of electrical signals in open - closed mode (controlled diode).

The simplest thyristor is a dinistor - an uncontrolled switching diode, which is a four-layer structure p-n-p-n type(Fig. 1.1.2). Here, as with other types of thyristors, the outer n-p-n junctions are called emitter, and the middle p-n junction is called collector. The internal areas of the structure lying between transitions are called bases. The electrode that provides electrical connection with the outer n-region is called the cathode, and with the outer p-region is called the anode.

Unlike asymmetrical thyristors (dinistors, trinistors), in symmetrical thyristors the reverse branch of the current-voltage characteristic has the form of a direct branch. This is achieved by connecting two identical four-layer structures back-to-back or using five-layer structures with four p-n junctions (triacs).

Rice. 1.1.1 Designations on the diagrams: a) triac b) dinistor c) trinistor.

Rice. 1.1.2 Structure of the dinistor.

Rice. 1.1.3 SCR structure.

1.2 Operating principle

When the dinistor is turned on according to the diagram shown in Fig. 1.2.1, the collector p-n junction is closed, and the emitter junctions are open. The resistance of open junctions is low, so almost all of the power supply voltage is applied to the collector junction, which has a high resistance. In this case, a small current flows through the thyristor (section 1 in Fig. 1.2.3).

Rice. 1.2.1. Scheme for connecting an uncontrolled thyristor (dinistor) to the circuit.

Rice. 1.2.2. Scheme for connecting a controlled thyristor (thyristor) to the circuit.

Fig.1.2.3. Current-voltage characteristic of the dinistor.

Fig.1.2.4. Current-voltage characteristic of a thyristor.

If you increase the voltage of the power source, the thyristor current increases slightly until this voltage approaches a certain critical value equal to the turn-on voltage Uon. At voltage Uon in the dinistor, conditions are created for avalanche multiplication of charge carriers in the region of the collector junction. A reversible electrical breakdown of the collector junction occurs (section 2 in Fig. 1.2.3). An excess concentration of electrons is formed in the n-region of the collector junction, and an excess concentration of holes is formed in the p-region. As these concentrations increase, the potential barriers of all dinistor transitions decrease. The injection of carriers through the emitter junctions increases. The process is avalanche-like in nature and is accompanied by switching of the collector transition to the open state. The current increases simultaneously with a decrease in the resistance of all areas of the device. Therefore, an increase in current through the device is accompanied by a decrease in voltage between the anode and cathode. On the current-voltage characteristic, this section is indicated by the number 3. Here the device has a negative differential resistance. The voltage across the resistor increases and the dinistor switches.

After the transition of the collector junction to the open state, the current-voltage characteristic has the form corresponding to the direct branch of the diode (section 4). After switching, the voltage on the dinistor decreases to 1 V. If you continue to increase the voltage of the power supply or decrease the resistance of resistor R, then an increase in the output current will be observed, as in the usual scheme with a diode when connected directly.

When the power supply voltage decreases, the high resistance of the collector junction is restored. The recovery time of the resistance of this junction can be tens of microseconds.

The voltage Uon at which an avalanche-like increase in current begins can be reduced by introducing non-majority charge carriers into any of the layers adjacent to the collector junction. Additional charge carriers are introduced into the thyristor by an auxiliary electrode powered from an independent source of control voltage (Ucontrol). A thyristor with an auxiliary control electrode is called a triode or trinistor. In practice, when using the term “thyristor”, it is precisely the element that is meant. The connection diagram for such a thyristor is shown in Fig. 1.2.2. The possibility of reducing voltage U with increasing control current is shown by the family of current-voltage characteristics (Fig. 1.2.4).

If a supply voltage of the opposite polarity is applied to the thyristor (Fig. 1.2.4), then the emitter junctions will be closed. In this case, the current-voltage characteristic of the thyristor resembles the reverse branch of the characteristic of a conventional diode. At very high reverse voltages, irreversible breakdown of the thyristor is observed.

Thyristor. Device, purpose.

A thyristor is a controlled three-electrode semiconductor device with three p–n-transitions, having two stable states of electrical equilibrium: closed and open.

The thyristor combines the functions of a rectifier, switch and amplifier. It is often used as a regulator, mainly when the circuit is powered by alternating voltage. The following points reveal the three main properties of a thyristor:

1 A thyristor, like a diode, conducts current in one direction, acting as a rectifier;

2 The thyristor is switched from the off state to the on state when a signal is applied to the control electrode and, therefore, like a switch, has two stable states.

3 the control current required to transfer the thyristor from the “closed” state to the “open” state is significantly less (several milliamps) with an operating current of several amperes and even several tens of amperes. Consequently, the thyristor has the properties of a current amplifier;

Design and main types of thyristors

Rice. 1. Thyristor circuits: a) Basic four-layer p-n-p-n-structure b) Diode thyristor c) Triode thyristor.

The basic diagram of the thyristor structure is shown in Fig. 1. It is a four-layer semiconductor structure p-n-p-n, containing three series-connected p-n-transition J1, J2, J3. Contact to external p-layer is called anode, to the outer n-layer - cathode. In general p-n-p-n-the device can have up to two control electrodes (bases) connected to the internal layers. By applying a signal to the control electrode, the thyristor is controlled (its state changes). A device without control electrodes is called diode thyristor or dinistor. Such devices are controlled by voltage applied between the main electrodes. A device with one control electrode is called triode thyristor or SCR(sometimes just a thyristor, although this is not entirely correct). Depending on which layer of the semiconductor the control electrode is connected to, SCRs can be anode and cathode controlled. The latter are the most common.

The devices described above come in two varieties: those that pass current in one direction (from the anode to the cathode) and those that pass current in both directions. In the latter case, the corresponding devices are called symmetrical(since their current-voltage characteristics are symmetrical) and usually have a five-layer semiconductor structure. Symmetrical SCR also called triac or triac(from English triac). It should be noted that instead of symmetrical dinistors, their integral analogues, which have better parameters, are often used.

Thyristors with a control electrode are divided into lockable and non-lockable. Non-lockable thyristors, as the name suggests, cannot be switched to the off state using a signal applied to the control electrode. Such thyristors turn off when the current flowing through them becomes less than the holding current. In practice, this usually occurs at the end of the half-wave of the mains voltage.

Current-voltage characteristic of a thyristor

Rice. 2. Current-voltage characteristic of the thyristor

A typical current-voltage characteristic of a thyristor conducting in one direction (with or without control electrodes) is shown in Fig. 2. It has several sections:

· Between points 0 and (Vо,IL) there is a section corresponding to the high resistance of the device - direct blocking (lower branch).

· At point Vvo the thyristor is turned on (the point at which the dinistor switches to the on state).

· Between the points (Vvo, IL) and (Vн,In) there is a section with negative differential resistance - an unstable region of switching to the on state. When a potential difference between the anode and cathode of a thyristor of direct polarity is applied greater than Vno, the thyristor is unlocked (dinistor effect).

· The section from the point with coordinates (Vн,In) and above corresponds to the open state (direct conduction)

· The graph shows the current-voltage characteristics with different currents control (currents on the control electrode of the thyristor) IG (IG=0; IG>0; IG>>0), and the greater the current IG, the lower the voltage Vbo the thyristor switches to a conducting state

· The dotted line indicates the so-called. “rectification switch-on current” (IG>>0), at which the thyristor goes into a conducting state at a minimum anode-cathode voltage. In order to transfer the thyristor back to a non-conducting state, it is necessary to reduce the current in the anode-cathode circuit below the rectification switch-on current.

· The section between 0 and Vbr describes the reverse blocking mode of the device.

The current-voltage characteristic of symmetrical thyristors differs from that shown in Fig. 2 in that the curve in the third quarter of the graph repeats sections 0-3 symmetrically relative to the origin.

Based on the type of nonlinearity of the current-voltage characteristic, the thyristor is classified as an S-device.

Various terms and symbols are often used in diagrams and technical documentation, but not all novice electricians know their meaning. We propose to discuss what power thyristors for welding are, their operating principle, characteristics and labeling of these devices.

What is a thyristor and their types

Many have seen thyristors in the “Running Fire” garland; this is the simplest example of the device described and how it works. A silicon rectifier or thyristor is very similar to a transistor. This is a multilayer semiconductor device, the main material of which is silicon, most often in a plastic housing. Due to the fact that its operating principle is very similar to a rectifying diode (AC rectifier devices or dinistors), the designation on the diagrams is often the same - this is considered an analogue of a rectifier.

There are:

• ABB turn-off thyristors (GTO),
• standard SEMIKRON,
• powerful avalanche type TL-171,
• optocouplers (say, TO 142-12.5-600 or MTOTO 80 module),
• symmetrical TS-106-10,
• low frequency MTTs,
• triac BTA 16-600B or VT for washing machines,
• frequency TBC,
• foreign TPS 08,
• TYN 208.

But at the same time, IGBT or IGCT type transistors are used for high-voltage devices (furnaces, machine tools, and other industrial automation).

But, unlike a diode, which is a two-layer (PN) transistor (PNP, NPN), a thyristor consists of four layers (PNPN) and this semiconductor device contains three p-n junctions. In this case, diode rectifiers become less efficient. This is well demonstrated by the thyristor control circuit, as well as any electricians’ reference book (for example, in the library you can read a book by the author Zamyatin for free).

A thyristor is a unidirectional AC converter, meaning it conducts current in one direction only, but unlike a diode, the device can be made to operate as an open circuit switch or as a DC rectifying diode. In other words, semiconductor thyristors can only operate in switching mode and cannot be used as amplification devices. The key on the thyristor is not capable of moving to the closed position on its own.

The silicon controlled rectifier is one of several power semiconductor devices, along with triacs, AC diodes, and unijunction transistors, that can switch from one mode to another very quickly. Such a thyristor is called high-speed. Of course, the class of the device plays a big role here.

Application of thyristor

The purpose of thyristors can be very different, for example, a homemade welding inverter based on thyristors is very popular, charger for a car (thyristor in the power supply) and even a generator. Due to the fact that the device itself can pass both low-frequency and high-frequency loads, it can also be used for a transformer for welding machines (their bridge uses exactly these parts). To control the operation of the part in this case, a voltage regulator on the thyristor is needed.

Don't forget about the ignition thyristor for motorcycles.

Description of design and principle of operation

The thyristor consists of three parts: “Anode”, “Cathode” and “Input”, consisting of three p-n junctions, which can switch between ON and OFF positions at very high speed. But at the same time, it can also be switched from the “ON” position for different durations, i.e., over several half-cycles, in order to deliver a certain amount of energy to the load. The operation of a thyristor can be better explained by assuming that it will consist of two transistors connected to each other, like a pair of complementary regenerative switches.

The simplest microcircuits demonstrate two transistors, which are combined in such a way that the collector current, after the “Start” command, flows into the NPN transistor TR 2 channels directly into the PNP transistor TR 1. At this time, the current from TR 1 flows into the channels into the bases of TR 2. These two interconnected transistors are arranged such that the base-emitter receives current from the collector-emitter of the other transistor. This requires parallel placement.

Despite all safety measures, the thyristor may involuntarily move from one position to another. This occurs due to a sharp jump in current, temperature changes and other various factors. Therefore, before you buy a thyristor KU202N, T122 25, T 160, T 10 10, you need to not only check it with a tester (ring), but also familiarize yourself with the operating parameters.

Typical thyristor current-voltage characteristics

To start discussing this complex topic, view the diagram of the current-voltage characteristics of the thyristor:

1. The segment between 0 and (Vо,IL) fully corresponds to direct locking of the device;
2. In the Vvo section, the thyristor is in the “ON” position;
3. The segment between zones (Vvo, IL) and (Vн,In) is the transition position in the on state of the thyristor. It is in this area that the so-called dinistor effect occurs;
4. In turn, points (Vн,In) show on the graph the direct opening of the device;
5. Points 0 and Vbr are the section where the thyristor is turned off;
6. This is followed by the segment Vbr - it indicates the reverse breakdown mode.

Naturally, modern high-frequency radio components in a circuit can affect the current-voltage characteristics in an insignificant way (coolers, resistors, relays). Also, symmetrical photothyristors, SMD zener diodes, optothyristors, triode, optocouplers, optoelectronic and other modules may have different current-voltage characteristics.

In addition, we draw your attention to the fact that in this case, device protection is carried out at the load input.

Thyristor check

Before you buy a device, you need to know how to test a thyristor with a multimeter. Connect meter You can only go to the so-called tester. The diagram by which such a device can be assembled is presented below:

According to the description, it is necessary to apply a positive voltage to the anode, and a negative voltage to the cathode. It is very important to use a value that matches the resolution of the thyristor. The drawing shows resistors with a nominal voltage of 9 to 12 volts, which means that the tester voltage is slightly higher than the thyristor. After you have assembled the device, you can begin to check the rectifier. You need to press the button that sends pulse signals to turn it on.

Testing the thyristor is very simple; a button briefly sends an opening signal (positive relative to the cathode) to the control electrode. After this, if the running lights on the thyristor come on, the device is considered inoperative, but powerful devices do not always react immediately after the load arrives.

In addition to checking the device, it is also recommended to use special controllers or a control unit for thyristors and triacs OWEN BOOST or other brands; it works approximately the same as a power regulator on a thyristor. The main difference is a wider range of voltages.

Video: operating principle of a thyristor

Specifications

Let's consider technical parameters thyristor series KU 202e. This series presents domestic low-power devices, the main use of which is limited to household appliances: it is used to operate electric furnaces, heaters, etc.

The drawing below shows the pinout and main parts of the thyristor.

1. Set reverse on-state voltage (max) 100 V
2. Closed voltage 100 V
3. Pulse in open position – 30 A
4. Repeated pulse in open position 10 A
5. Medium voltage<=1,5 В
6. Non-unlocking voltage >=0.2 V
7. Set current in open position<=4 мА
8. Reverse current<=4 мА
9. Constant type unlocking current<=200 мА
10. Set constant voltage<=7 В
11. On time<=10 мкс
12. Shutdown time<=100 мкс

The device turns on within microseconds. If you need to replace the described device, then consult a sales consultant at an electrical store - he will be able to select an analogue according to the diagram.

The price of a thyristor depends on its brand and characteristics. We recommend buying domestic devices - they are more durable and affordable. In spontaneous markets you can buy a high-quality, powerful converter for up to a hundred rubles.