Thyristor - operating principle, device and control circuit. Thyristors. Device, principle of operation, current-voltage characteristics

Thyristor is semiconductor device, designed to work as a key. It has three electrodes and a p-n-p-n structure of four layers semiconductor. The electrodes are referred to as anode, cathode and control electrode. The p-n-p-n structure is functionally similar to a nonlinear resistor, which is capable of accepting two states:

• with very high resistance, switched off;
• with very low resistance, switched on.

Species

The switched-on thyristor maintains a voltage of about one or several volts, which increases slightly with increasing current flowing through it. Depending on the type of current and voltage applied to the electrical circuit with a thyristor, it uses one of three modern varieties these semiconductor devices. The following operate on direct current:

• switchable thyristors;
• three types of turn-off thyristors, referred to as

Triacs operate on alternating and direct current. All these thyristors contain a control electrode and two other electrodes through which the load current flows. For SCRs and turn-off thyristors, these are the anode and cathode; for triacs, the name of these electrodes is determined by the correct determination of the properties of the control signal supplied to the control electrode.

Presence in thyristor p-n-p-n structures allows us to divide it conditionally into two areas, each of which is bipolar transistor appropriate conductivity. Thus, these interconnected transistors are the equivalent of a thyristor, as shown in the diagram on the left. SCRs were the first to appear on the market.

Properties and characteristics

In essence, this is an analogue of a self-locking relay with one normally open contact, the role of which is played by a semiconductor structure located between the anode and cathode. The difference from a relay is that this semiconductor device can have several switching methods. All these methods are explained by the transistor equivalent of the SCR.

Two equivalent transistors are covered by positive feedback. It greatly enhances any current changes in their semiconductor junctions. Therefore, there are several types of influence on the electrodes of the thyristor to turn it on and off. The first two methods allow you to switch on the anode.

• If the voltage at the anode is increased, at a certain value, the effects of the incipient breakdown of the semiconductor structures of transistors will begin to affect. The initial current that appears will be amplified by positive feedback and both transistors will turn on.
• When enough rapid increase voltage at the anode, the interelectrode capacitances, which are present in any electronic components, are charged. At the same time, charging currents of these capacitors appear in the electrodes, which are picked up by positive feedback and it all ends with the SCR turning on.

If the above voltage changes are absent, switching usually occurs with the base current equivalent n-p-n transistor. You can turn off the thyristor in one of two ways, which also become clear due to the interaction of equivalent transistors. Positive feedback in them operates starting from certain values ​​of currents flowing in the p-n-p-n structure. If the current value is made less than these values, positive feedback will work to quickly disappear the currents.

Another shutdown method is using positive interrupt feedback a voltage pulse that changes polarity at the anode and cathode. With this effect, the direction of the currents between the electrodes changes to the opposite and the thyristor turns off. Since semiconductor materials are characterized by the phenomenon of the photoelectric effect, there are photo- and optothyristors, in which the switching on can be caused by illumination of either the receiving window or the LED in the body of this semiconductor device.

There are also so-called dinistors (uncontrolled thyristors). These semiconductor devices do not have a control electrode by design. At its core, it is a thyristor with one missing terminal. Therefore, their state depends only on the voltage of the anode and cathode and they cannot be turned on by a control signal. Otherwise, the processes in them are similar to conventional thyristors. The same applies to triacs, which are essentially two thyristors connected in parallel. Therefore, they are used to control alternating current without additional diodes.

Lockable thyristors

If you manufacture areas of the p-n-p-n structure near the bases of equivalent transistors in a certain way, you can achieve complete controllability of the thyristor from the control electrode. This p-n-p-n structure design is shown in the image on the left. Such a thyristor can be turned on and off with appropriate signals at any time by sending them to the control electrode. Other switching methods applied to thyristors are also suitable for turn-off thyristors.

However, these methods are not applicable to such semiconductor devices. On the contrary, they are excluded by certain circuit solutions. The goal is to achieve reliable switching on and off using only the control electrode. This is necessary for the use of such thyristors in powerful inverters increased frequency. GTOs operate at frequencies up to 300 Hertz, and IGCTs are capable of significantly higher frequencies, reaching 2 kHz. Rated currents can be several thousand amperes, and voltages can be several kilovolts.

A comparison of different thyristors is given in the table below.

Thyristors are manufactured for a wide range of currents and voltages. Their design is determined by the dimensions of the p-n-p-n structure and the need to obtain reliable heat removal from it. Modern thyristors, as well as their designations on electrical diagrams shown in the images below.

♦ As we have already found out, a thyristor is a semiconductor device that has the properties of an electric valve. Thyristor with two terminals (A - anode, K - cathode) , this is a dinistor. Thyristor with three terminals (A – anode, K – cathode, Ue – control electrode) , this is a thyristor, or in everyday life it is simply called a thyristor.

♦ Using the control electrode (under certain conditions), you can change the electrical state of the thyristor, that is, transfer it from the “off” state to the “on” state.
The thyristor opens if the applied voltage between the anode and cathode exceeds the value U = Upr, that is, the magnitude of the breakdown voltage of the thyristor;
The thyristor can be opened at a voltage less than Upr between anode and cathode (U< Uпр) , if you apply a voltage pulse of positive polarity between the control electrode and the cathode.

♦ The thyristor can remain in the open state for as long as desired, as long as the supply voltage is applied to it.
The thyristor can be closed:

• - if you reduce the voltage between the anode and cathode up to U = 0;
• - if you reduce the anode current of the thyristor to a value less than the holding current Iud.
• — by applying a blocking voltage to the control electrode (only for turn-off thyristors).

The thyristor can also remain in the closed state for any length of time until the triggering pulse arrives.
Thyristors and dinistors operate both in DC and DC circuits AC.

Operation of dinistor and thyristor in circuits DC.

Let's look at some practical examples.
The first example of using a dinistor is relaxation sound generator .

We use it as a dinistor KN102A-B.

♦ The generator works as follows.
When the button is pressed Kn, through resistors R1 and R2 The capacitor gradually charges WITH(+ batteries – closed contacts buttons Kn - resistors - capacitor C - battery minus).
A chain of a telephone capsule and a dinistor is connected in parallel to the capacitor. No current flows through the telephone capsule and the dinistor, since the dinistor is still “locked”.
♦ When the capacitor reaches the voltage at which the dynistor breaks through, a pulse of capacitor discharge current passes through the telephone capsule coil (C – telephone coil – dynistor – C). A click is heard from the phone, the capacitor is discharged. Next again charging capacitor C and the process repeats.
The frequency of repetition of clicks depends on the capacitance of the capacitor and the resistance value of the resistors R1 and R2.
♦ With the voltage, resistor and capacitor ratings indicated on the diagram, the frequency sound signal using resistor R2 you can change within 500 – 5000 hertz. The telephone capsule must be used with a low-impedance coil 50 – 100 Ohm, no more, for example a telephone capsule TK-67-N.
The telephone capsule must be connected with correct polarity, otherwise it will not work. On the capsule there is a designation + (plus) and – (minus).

♦ This scheme (Figure 1) has one drawback. Due to the large spread of dinistor parameters KN102(different breakdown voltage), in some cases, it will be necessary to increase the power supply voltage to 35 – 45 volts, which is not always possible and convenient.

A control device assembled on a thyristor for turning on and off the load using one button is shown in Fig. 2.

The device works as follows.
♦ B original condition The thyristor is closed and the light does not light.
Press the Kn button for 1 – 2 seconds. The button contacts open, the thyristor cathode circuit is broken.

At this moment the capacitor WITH charged from a power source through a resistor R1. The voltage across the capacitor reaches U power supply.
Release the button Kn.
At this moment, the capacitor is discharged through the circuit: resistor R2 - control electrode of the thyristor - cathode - closed contacts of the Kn button - capacitor.
Current will flow in the control electrode circuit, thyristor "will open".
The light comes on and along the circuit: plus batteries - load in the form of a light bulb - thyristor - closed contacts of the button - minus batteries.
The circuit will remain in this state for as long as desired. .
In this state, the capacitor is discharged: resistor R2, transition control electrode - thyristor cathode, contacts of the button Kn.
♦ To turn off the light bulb, briefly press the button Kn. In this case, the main power supply circuit of the light bulb is interrupted. Thyristor "closes". When the contacts of the button are closed, the thyristor will remain in the closed state, since the control electrode of the thyristor Uynp = 0(capacitor is discharged).

I have tested and worked reliably in this scheme various thyristors:KU101, T122, KU201, KU202, KU208 .

♦ As already mentioned, the dinistor and thyristor have their own transistor analogue .

The thyristor analogue circuit consists of two transistors and is shown in Fig. 3.
Transistor Tr 1 has p-n-p conductivity, transistor Tr 2 has n-p-n conductivity. Transistors can be either germanium or silicon.

The thyristor analogue has two control inputs.
First entry: A – Ue1(emitter - base of transistor Tr1).
Second entrance: K – Ue2(emitter - base of transistor Tr2).

The analogue has: A - anode, K - cathode, Ue1 - the first control electrode, Ue2 - the second control electrode.

If control electrodes are not used, then it will be a dinistor, with electrodes A - anode and K - cathode .

♦ A pair of transistors, for an analogue of a thyristor, must be selected of the same power with a current and voltage higher than that required for the operation of the device. Thyristor analog parameters (breakdown voltage Unp, holding current Iyд) , will depend on the properties of the transistors used.

♦ For more stable analog operation, resistors are added to the circuit R1 and R2. And using a resistor R3 breakdown voltage can be adjusted Upr and holding current Iyd analogue of a dinistor - a thyristor. A diagram of such an analogue is shown in Fig 4.

If in the generator circuit audio frequencies (Figure 1), instead of a dinistor KN102 turn on the dinistor analogue, you get a device with different properties (Figure 5) .

The supply voltage of such a circuit will be from 5 to 15 volts. Changing resistor values R3 and R5 You can change the tone of the sound and the operating voltage of the generator.

Variable resistor R3 The breakdown voltage of the analogue is selected for the supply voltage used.

Then you can replace it with a constant resistor.

Transistors Tr1 and Tr2: KT502 and KT503; KT814 and KT815 or any others.

♦ Interesting voltage stabilizer circuit with protection from short circuit under load (Figure 6).

If the load current exceeds 1 ampere, the protection will work.

The stabilizer consists of:

• - control element - zener diode KS510, which determines the output voltage;
• - actuator transistors KT817A, KT808A, acting as a voltage regulator;
• - a resistor is used as an overload sensor R4;
• — the actuator protection mechanism uses an analogue of a dinistor, on transistors KT502 and KT503.

♦ At the input of the stabilizer there is a capacitor as a filter C1. Resistor R1 the stabilization current of the zener diode is set KS510, size 5 – 10 mA. The voltage across the zener diode should be 10 volts.
Resistor R5 sets the initial mode of output voltage stabilization.

Resistor R4 = 1.0 Ohm, is connected in series to the load circuit. The greater the load current, the more voltage proportional to the current is released across it.

In the initial state, when the load at the output of the stabilizer is small or turned off, the thyristor analogue is closed. The voltage of 10 volts applied to it (from the zener diode) is not enough for breakdown. At this moment the voltage drop across the resistor R4 almost equal to zero.
If you gradually increase the load current, the voltage drop across the resistor will increase R4. At a certain voltage on R4, the thyristor analogue breaks through and the voltage is established between the point Point1 and a common wire equal to 1.5 - 2.0 volts.
This is the voltage of the anode-cathode transition of an open analogue of a thyristor.

At the same time the LED lights up D1, signaling an emergency. The voltage at the output of the stabilizer, at this moment, will be equal to 1.5 - 2.0 volts.
To restore normal work stabilizer, you need to turn off the load and press the button Kn, resetting the security lock.
There will be voltage again at the output of the stabilizer 9 volts, and the LED will go out.
Setting the resistor R3, you can select the protection operation current from 1 ampere or more . Transistors T1 and T2 Can be installed on one radiator without insulation. The radiator itself should be isolated from the housing.

In order to clearly imagine the work, it is necessary to give an idea of ​​​​the essence of the work of a thyristor.

A controlled conductor consisting of four semiconductor transitions P-N-P-N. Its operating principle is similar to that of a diode and is carried out when an electric current is supplied to the control electrode.

The passage of current through the thyristor is only possible if the anode potential is higher than the cathode potential. The current through the thyristor stops passing when the current value drops to the closing threshold. The current that flows to the control electrode does not affect the current value in the main part of the thyristor and, in addition, it does not need constant support in the main state of the thyristor; it is needed solely to open the thyristor.

There are several decisive characteristics of a thyristor

In an open state, favorable for the current-carrying function, the thyristor is characterized by the following indicators:

• Voltage drop, it is determined as the threshold voltage using internal resistance.
• The maximum permissible current value is up to 5000 A, rms value typical for the most powerful components.

In the locked state of the thyristor it is:

• Direct maximum permissible voltage (higher than 5000A).
• In general, the forward and reverse voltage values ​​are the same.
• The turn-off time or the time with a minimum value during which the thyristor is not influenced by the positive value of the anode voltage relative to the cathode, otherwise the thyristor will spontaneously unlock.
• Control current characteristic of the open main part of the thyristor.

There are thyristors designed to operate in circuits designed for low frequencies and for circuits with high frequencies. These are so-called high-speed thyristors; their scope of application is designed for several kilohertz. High-speed thyristors are characterized by the use of unequal forward and reverse voltages.

To increase the constant voltage value

Rice. No. 1. Overall connection dimensions and drawing of the thyristor. m 1, m 2 –control points, in which the measurement occurs impulse voltage during open state. L 1 min – the smallest air gap (distance) in air between the terminals of the anode and the control electrode; L 2 min – minimum distance current passage length leaks between terminals.

Types of thyristors

• – diode thyristor, has two terminals anode and cathode.
• SCR – a triode thyristor is equipped with an additional control electrode.
• A triac is a symmetrical thyristor; it is an anti-series connection of thyristors and has the ability to pass current in the forward and reverse directions.

Rice. No. 2. Structure (a) and current-voltage characteristic (volt-ampere characteristic) of the thyristor.

Thyristors are designed to operate in circuits with different frequency limits, in normal applications thyristors can be connected to diodes, which are connected in a back-to-back manner, this property is used to increase constant voltage, the value of which the component can withstand in the off state. For advanced circuits it is used thyristorGTO (Gate Turn Oee – lockable thyristor), it is completely manageable. Its locking occurs via the control electrode. The use of thyristors of this kind has found application in very powerful converters, since it can pass high currents.

Write comments, additions to the article, maybe I missed something. Take a look at, I will be glad if you find anything else useful on mine.

A thyristor is an electronic component made from semiconductor materials, can consist of three or more p-n junctions and has two stable states: closed (low conductivity), open (high conductivity).

This is a dry formulation, which is for those who are just starting master electrical engineering uh, it says absolutely nothing. Let's look at the operating principle of this electronic component to ordinary people, so to speak, for dummies, and where it can be applied. Essentially, it's the electronic equivalent of the switches you use every day.

There are many types of these elements that have different characteristics and having various areas of application. Consider an ordinary single-operation thyristor.

The designation method on the diagrams is shown in Figure 1.

The electronic element has the following conclusions:

• anode positive terminal;
• cathode negative terminal;
• control electrode G.

The operating principle of a thyristor

The main application of this type of elements is the creation on their basis of power thyristor switches for switching high currents and regulating them. Switching on is carried out by a signal transmitted to the control electrode. In this case, the element is not fully controllable, and to close it it is necessary to use additional measures that will ensure that the voltage drops to zero.

If we talk about how a thyristor works in simple language, then, by analogy with a diode, it can conduct current only in one direction, so when connecting it you need observe correct polarity. When voltage is applied to the anode and cathode, this element will remain closed until the corresponding electrical signal. Now, regardless of the presence or absence of a control signal, it will not change its state and will remain open.

Terms thyristor closing:

1. Remove the signal from the control electrode;
2. Reduce the voltage at the cathode and anode to zero.

For AC networks, meeting these conditions does not pose any particular difficulties. The sinusoidal voltage, changing from one amplitude value to another, decreases to a zero value, and if at this moment there is no control signal, the thyristor will close.

In the case of using thyristors in direct current circuits, a number of methods are used for forced commutation (closing the thyristor), the most common is the use of a capacitor that has been pre-charged. The circuit with the capacitor is connected to the thyristor control circuit. When a capacitor is connected to the circuit, a discharge will occur to the thyristor, the discharge current of the capacitor will be directed opposite to the forward current of the thyristor, which will lead to a decrease in the current in the circuit to zero and the thyristor will close.

You might think that the use of thyristors is unjustified; isn't it easier to use a regular switch? A huge advantage of the thyristor is that it allows you to switch huge currents in the anode-cathode circuit using a negligible control signal supplied to the control circuit. In this case, no sparking occurs, which is important for the reliability and safety of the entire circuit.

Connection diagram

The control circuit may look different, but in the simplest case, the thyristor switch switching circuit looks like that shown in Figure 2.

A light bulb is attached to the anode L, and switch K2 connects the positive terminal of the power source G. B. The cathode is connected to the negative terminal of the power supply.

After power is supplied by switch K2, battery voltage will be applied to the anode and cathode, but the thyristor remains closed and the light does not light. In order to turn on the lamp, you need to press the K1 button, the signal through resistance R will be sent to the control electrode, the thyristor switch will change its state to open, and the lamp will light up. Resistance limits the current supplied to the control electrode. Pressing the K1 button again does not have any effect on the state of the circuit.

To close the electronic key, you need to disconnect the circuit from the power source using switch K2. This type electronic components will close, and if the supply voltage at the anode decreases to a certain value, which depends on its characteristics. This is how you can describe how a thyristor for dummies works.

Characteristics

The main characteristics include the following:

The elements in question, except electronic keys, are often used in power regulators, which allow you to change the power supplied to the load by changing the average and current values AC. The current value is regulated by changing the moment at which the opening signal is supplied to the thyristor (by varying the opening angle). The opening (regulation) angle is the time from the beginning of the half-cycle to the moment the thyristor opens.

Electronic Component Data Types

There are quite a few various types thyristors, but the most common, in addition to those we discussed above, are the following:

• dinistor element, switching of which occurs when a certain value of the voltage applied between the anode and cathode is reached;
• triac;
• an optothyristor, the switching of which is carried out by a light signal.

Triacs

I would like to dwell in more detail on triacs. As mentioned earlier, thyristors can only conduct current in one direction, therefore, when installed in an alternating current circuit, such a circuit regulates one half-cycle of the mains voltage. To regulate both half-cycles, it is necessary to install another thyristor back-to-back or use special circuits using powerful diodes or diode bridges. All this complicates the scheme, making it cumbersome and unreliable.

It is for such cases that the triac was invented. Let's talk about it and the principle of operation for dummies. The main difference between triacs from the elements discussed above lies in the ability to pass current in both directions. Essentially, these are two thyristors with general management, connected back-to-back (Figure 3 A).

Conditional graphic designation this electronic component is shown in Fig. 3 V. It should be noted that it will not be correct to call the power terminals anode and cathode, since the current can be conducted in any direction, so they are designated T1 and T2. The control electrode is designated G. In order to open the triac, it is necessary to apply a control signal to the corresponding output. The conditions for the transition of a triac from one state to another and back in AC networks do not differ from the control methods discussed above.

This type of electronic components is used in industrial applications, household appliances and power tools to continuously regulate current. This is the control of electric motors, heating elements, chargers.

In conclusion, I would like to say that both thyristors and triacs, while switching significant currents, have very modest sizes, while significant thermal power is released on their body. Simply put, they get very hot, so to protect the elements from overheating and thermal breakdown, they use a heat sink, which in the simplest case is an aluminum radiator.

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 analogs are often used, which have the best parameters.

Thyristors with a control electrode are divided into lockable and non-lockable. Non-latching thyristors, as the name suggests, cannot be turned off by 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 control currents (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.