Thyristor for dummies: switching circuit and control methods. How powerful power thyristors work

♦ 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 in both direct and alternating current circuits.

Operation of dinistor and thyristor in DC circuits.

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 of the Kn button – resistors – capacitor C – minus batteries).
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 dinistor breaks through, a pulse of capacitor discharge current passes through the coil of the telephone capsule (C - telephone coil - dinistor - C). A click is heard from the phone, the capacitor is discharged. Next, capacitor C is charged again 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 of the sound signal using resistor R2 can be changed 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.
♦ In the initial state, 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 on the control electrode of the thyristor Uynp = 0(capacitor is discharged).

I have tested and worked reliably various thyristors in this circuit: 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 audio frequency generator circuit (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 load short circuit protection (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 operation of the 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.

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

A thyristor is a semiconductor element that has 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 principle of operation 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 circuits with variable voltage, as a rule, the thyristor is reset according to the second option. Alternating current in a household network has a sinusoidal shape when its value approaches zero and a reset occurs. 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 a constant voltage circuit, after a short-term voltage appears 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 switching power supplies are built. 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 the technical specifications in front of your eyes when making a test, you can at the same time 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 varies from series to series - you should not pay special attention to this. 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. They are opened by applying high voltage to the anode and cathode in the form of a pulse. 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. Goes into the 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 a 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, rectifiers, pulsed current sources, 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 made in a 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.

Good evening habr. Let's talk about such a device as a thyristor. A thyristor is a bistable semiconductor device having three or more interacting rectifying junctions. In terms of functionality, they can be compared to electronic keys. But there is one feature in the thyristor: it cannot go into the closed state, unlike a regular key. Therefore, it can usually be found under the name - not fully managed key.

The figure shows a typical view of a thyristor. It consists of four alternating types of electrical conductivity of semiconductor regions and has three terminals: anode, cathode and control electrode.
The anode is in contact with the outer p-layer, the cathode is in contact with the outer n-layer.
You can refresh your memory about the p-n junction.

Classification

Operating principle

In connection with this pattern, the outer regions can be called emitter, and the central junction can be called collector.
To understand how a thyristor works, you should look at the current-voltage characteristic.


A small positive voltage is applied to the anode of the thyristor. The emitter junctions are connected in the forward direction, and the collector junctions in the reverse direction. (essentially all the tension will be on it). The section from zero to one on the current-voltage characteristic will be approximately similar to the reverse branch of the diode characteristic. This mode can be called the thyristor closed state mode.
As the anode voltage increases, majority carriers are injected into the base region, thereby accumulating electrons and holes, which is equivalent to the potential difference at the collector junction. As the current through the thyristor increases, the voltage at the collector junction will begin to decrease. And when it decreases to a certain value, our thyristor will go into a state of negative differential resistance (section 1-2 in the figure).
After this, all three transitions will shift in the forward direction, thereby transferring the thyristor to the open state (section 2-3 in the figure).
The thyristor will remain in the open state as long as the collector junction is biased in the forward direction. If the thyristor current is reduced, then as a result of recombination the number of nonequilibrium carriers in the base regions will decrease and the collector junction will be biased in the opposite direction and the thyristor will go into the off state.
When the thyristor is turned on in reverse, the current-voltage characteristic will be similar to that of two diodes connected in series. The reverse voltage will be limited in this case by the breakdown voltage.

General parameters of thyristors

Conclusion

Reverse locking mode

Rice. 3. Thyristor reverse blocking mode

Two main factors limit the regime of reverse breakdown and forward breakdown:

1. Puncture of the depleted area.

In the reverse blocking mode, a voltage is applied to the anode of the device, negative with respect to the cathode; junctions J1 and J3 are reverse biased, and junction J2 is forward biased (see Fig. 3). In this case, most of the applied voltage drops at one of the junctions J1 or J3 (depending on the degree of doping of the various regions). Let this be transition J1. Depending on the thickness W n1 of the n1 layer, the breakdown is caused by avalanche multiplication (the thickness of the depletion region during breakdown is less than W n1) or puncture (the depletion layer spreads over the entire n1 region, and the junctions J1 and J2 are closed).

Direct locking mode

With direct blocking, the voltage at the anode is positive with respect to the cathode and only junction J2 is reverse biased. Junctions J1 and J3 are forward biased. Most of the applied voltage drops at junction J2. Through junctions J1 and J3, minority carriers are injected into the regions adjacent to junction J2, which reduce the resistance of junction J2, increase the current through it and reduce the voltage drop across it. As the forward voltage increases, the current through the thyristor initially increases slowly, which corresponds to the 0-1 section on the current-voltage characteristic. In this mode, the thyristor can be considered locked, since the resistance of junction J2 is still very high. As the voltage across the thyristor increases, the proportion of voltage across J2 decreases and the voltages across J1 and J3 increase faster, causing the current through the thyristor to further increase and increasing minority carrier injection into the region of J2. At a certain voltage value (of the order of tens or hundreds of volts), it is called the switching voltage V BF(point 1 on the current-voltage characteristic), the process acquires an avalanche-like character, the thyristor goes into a state with high conductivity (turns on), and a current is established in it, determined by the source voltage and the resistance of the external circuit.

Two-transistor model

To explain the characteristics of the device in direct blocking mode, a two-transistor model is used. A thyristor can be considered as a connection of a pnp transistor to an npn transistor, with the collector of each connected to the base of the other, as shown in Fig. 4 for triode thyristor. The central junction acts as a collector of holes injected by junction J1 and electrons injected by junction J3. Relationship between emitter currents I E, collector I C and bases I B and the static current gain α 1 p-n-p transistor is also shown in Fig. 4, where I Co is the reverse saturation current of the collector-base junction.

Rice. 4. Two-transistor model of a triode thyristor, connection of transistors and current ratio in a pnp transistor.

Similar relationships can be obtained for an n-p-n transistor when the direction of the currents is reversed. From Fig. 4 it follows that the collector current of the n-p-n transistor is at the same time the base current of the p-n-p transistor. Similarly, the collector current of the p-n-p transistor and the control current Ig flow into the base of the n-p-n transistor. As a result, when the total gain in the closed loop exceeds 1, a regenerative process becomes possible.

The base current of the pnp transistor is I B1= (1 - α 1) I A - I Co1. This current also flows through the collector of the npn transistor. The collector current of an n-p-n transistor with gain α 2 is equal to I C2= α 2 I K + ICo2.

Equating I B1 And I C2, we get (1 - α 1) I A - I Co1= α 2 I K + ICo2. Because I K = I A + Ig, That

Rice. 5. Energy band diagram in forward bias mode: equilibrium state, forward blocking mode and forward conduction mode.

This equation describes the static characteristics of the device in the voltage range up to breakdown. After breakdown, the device operates as a p-i-n diode. Note that all terms in the numerator of the right side of the equation are small, therefore, while the term α 1 + α 2< 1, ток I A small (Coefficients α1 and α2 themselves depend on I A and usually grow with increasing current) If α1 + α2 = 1, then the denominator of the fraction goes to zero and a direct breakdown occurs (or the thyristor is turned on). It should be noted that if the polarity of the voltage between the anode and cathode is reversed, then junctions J1 and J3 will be reverse biased, and J2 forward biased. Under such conditions, breakdown does not occur, since only the central junction acts as an emitter and the regenerative process becomes impossible.

The width of the depletion layers and energy band diagrams at equilibrium, in the direct blocking and direct conduction modes are shown in Fig. 5. In equilibrium, the depletion region of each transition and the contact potential are determined by the impurity distribution profile. When a positive voltage is applied to the anode, junction J2 tends to be reverse biased, while junctions J1 and J3 tend to be forward biased. The voltage drop between the anode and the cathode is equal to the algebraic sum of the voltage drops across the transitions: V AK = V 1 + V 2 + V 3. As the voltage increases, the current through the device increases and, therefore, α1 and α2 increase. Due to the regenerative nature of these processes, the device will eventually go into an open state. Once the thyristor is turned on, the current flowing through it must be limited by the external load resistance, otherwise the thyristor will fail if the voltage is high enough. In the on state, junction J2 is biased in the forward direction (Fig. 5, c), and the voltage drop V AK = (V 1 - | V 2| + V 3) is approximately equal to the sum of the voltage across one forward-biased junction and the voltage across the saturated transistor.

Direct conduction mode

When the thyristor is in the on state, all three junctions are forward biased. Holes are injected from region p1, and electrons are injected from region n2, and the n1-p2-n2 structure behaves similarly to a saturated transistor with the diode contact removed to region n1. Therefore, the device as a whole is similar to a p-i-n (p + -i-n +) diode...

Classification of thyristors

• diode thyristor (additional name "dinistor") - a thyristor with two terminals
  • Diode thyristor, non-reverse conducting
  • diode thyristor, conducting in the opposite direction
  • Diode symmetrical thyristor (additional name "diac")
• triode thyristor (additional name "thyristor") - a thyristor with three terminals
  • triode thyristor, not conducting in the opposite direction (additional name "thyristor")
  • triode thyristor, conducting in the opposite direction (additional name "thyristor-diode")
  • triode symmetrical thyristor (additional name "triac", informal name "triac")
  • triode thyristor asymmetric
  • switchable thyristor (additional name "triode switchable thyristor")

The difference between a dinistor and a trinistor

There are no fundamental differences between a dinistor and a trinistor, however, if the opening of a dinistor occurs when a certain voltage is reached between the anode and cathode terminals, depending on the type of a given dinistor, then in a trinistor the opening voltage can be specially reduced by applying a current pulse of a certain duration and magnitude to its control electrode with a positive potential difference between the anode and cathode, and the trinistor design differs only in the presence of a control electrode. SCRs are the most common devices from the “thyristor” family.

The difference between a triode thyristor and a turn-off thyristor

Switching to the closed state of conventional thyristors is carried out either by reducing the current through the thyristor to the value Ih, or by changing the voltage polarity between the cathode and anode.

Switchable thyristors, unlike conventional thyristors, under the influence of the control electrode current can transition from a closed state to an open state, and vice versa. To close a turn-off thyristor, it is necessary to pass a current of opposite polarity through the control electrode than the polarity that caused it to open.

Triac

A triac (symmetrical thyristor) is a semiconductor device, in its structure it is analogous to the back-to-back connection of two thyristors. Capable of passing electric current in both directions.

Characteristics of thyristors

Modern thyristors are manufactured for currents from 1 mA to 10 kA; for voltages from several V to several kV; the rate of increase in the forward current in them reaches 10 9 A/s, voltage - 10 9 V/s, the on time ranges from several tenths to several tens of microseconds, the off time ranges from several units to several hundred microseconds; Efficiency reaches 99%.

Application

• Controlled rectifiers
• Converters (inverters)
• Power regulators (dimmers)

See also

• CDI (Capacitor Discharge Ignition)

Notes

Literature

• GOST 15133-77.
• Kublanovsky. Ya. S. Thyristor devices. - 2nd ed., revised. and additional - M.: Radio and Communications, 1987. - 112 p.: ill. - (Mass Radio Library. Issue 1104).

Links

• Thyristors: principle of operation, designs, types and methods of inclusion
• Control of thyristors and triacs via a microcontroller or digital circuit
• Converter devices in power supply systems
• Rogachev K.D. Modern power switched thyristors.
• Domestic Analogues of Imported Thyristors
• Directories on thyristors and analogues, Replacing thyristors, replacing diodes. Zener diodes

- a device with the properties of a semiconductor, the design of which is based on a single-crystal semiconductor having three or more p-n junctions.

Its operation implies the presence of two stable phases:

• “closed” (conductivity level is low);
• “open” (conductivity level is high).

Thyristors are devices that perform the functions of power electronic switches. Another name for them is single-operation thyristors. This device allows you to regulate the impact of powerful loads through minor impulses.

According to the current-voltage characteristic of the thyristor, an increase in the current in it will provoke a decrease in voltage, that is, a negative differential resistance will appear.

In addition, these semiconductor devices can connect circuits with voltages up to 5000 Volts and currents up to 5000 Amps (at a frequency of no more than 1000 Hz).

Thyristors with two and three terminals are suitable for operation with both direct and alternating current. Most often, the principle of their operation is compared with the operation of a rectifying diode and it is believed that they are a full-fledged analogue of a rectifier, in some sense even more effective.

The types of thyristors differ from each other:

• Control method.
• Conductivity (unilateral or bilateral).

General management principles

The thyristor structure has 4 semiconductor layers in a series connection (p-n-p-n). The contact connected to the outer p-layer is the anode, and the contact connected to the outer n-layer is the cathode. As a result, with a standard assembly, a thyristor can have a maximum of two control electrodes, which are attached to the internal layers. According to the connected layer, the conductors are divided into cathode and anode based on the type of control. The first type is most often used.

The current in thyristors flows towards the cathode (from the anode), so the connection to the current source is made between the anode and the positive terminal, as well as between the cathode and the negative terminal.

Thyristors with a control electrode can be:

• Lockable;
• Unlockable.

An indicative property of non-locking devices is their lack of response to a signal from the control electrode. The only way to close them is to reduce the level of current flowing through them so that it is inferior to the holding current.

When controlling a thyristor, some points should be taken into account. A device of this type changes operating phases from “off” to “on” and back in jumps and only under the condition of external influence: using current (voltage manipulation) or photons (in cases with a photothyristor).

To understand this point, you need to remember that a thyristor mainly has 3 outputs (thyristor): anode, cathode and control electrode.

The UE (control electrode) is precisely responsible for turning the thyristor on and off. The opening of the thyristor occurs under the condition that the applied voltage between A (anode) and K (cathode) becomes equal to or exceeds the operating voltage of the thyristor. True, in the second case, exposure to a pulse of positive polarity between Ue and K will be required.

With a constant supply of supply voltage, the thyristor can be open indefinitely.

To switch it to a closed state, you can:

• Reduce the voltage level between A and K to zero;
• Reduce the A-current value so that the holding current strength is greater;
• If the operation of the circuit is based on the action of alternating current, the device will turn off without outside intervention when the current level itself drops to zero reading;
• Apply a blocking voltage to the UE (relevant only for lockable types of semiconductor devices).

The closed state also lasts indefinitely until a triggering impulse occurs.

Specific control methods

• Amplitude .

It represents the supply of a positive voltage of varying magnitude to the Ue. The opening of the thyristor occurs when the voltage value is sufficient to break through the control transition of the rectifying current (Irev). By changing the voltage on the UE, it becomes possible to change the opening time of the thyristor.

The main disadvantage of this method is the strong influence of the temperature factor. In addition, each type of thyristor will require a different type of resistor. This point does not add ease of use. In addition, the opening time of the thyristor can be adjusted only while the first 1/2 of the positive half-cycle of the network lasts.

• Phase.

It consists of changing the phase Ucontrol (in relation to the voltage at the anode). In this case, a phase shift bridge is used. The main disadvantage is the low slope of Ucontrol, so it is possible to stabilize the opening moment of the thyristor only for a short time.

• Pulse-phase .

Designed to overcome the shortcomings of the phase method. For this purpose, a voltage pulse with a steep edge is applied to Ue. This approach is currently the most common.

Thyristors and safety

Due to the impulse nature of their action and the presence of reverse recovery current, thyristors greatly increase the risk of overvoltage in the operation of the device. In addition, the danger of overvoltage in the semiconductor zone is high if there is no voltage at all in other parts of the circuit.

Therefore, in order to avoid negative consequences, it is customary to use CFTP schemes. They prevent the appearance and retention of critical voltage values.

Two-transistor thyristor model

From two transistors it is quite possible to assemble a dinistor (thyristor with two terminals) or a trinistor (thyristor with three terminals). To do this, one of them must have p-n-p conductivity, the other - n-p-n conductivity. Transistors can be made from either silicon or germanium.

The connection between them is carried out through two channels:

• Anode from the 2nd transistor + Control electrode from the 1st transistor;
• Cathode from the 1st transistor + Control electrode from the 2nd transistor.

If you do without the use of control electrodes, then the output will be a dinistor.

The compatibility of the selected transistors is determined by the same amount of power. In this case, the current and voltage readings must necessarily be greater than those required for the normal functioning of the device. Data on breakdown voltage and holding current depend on the specific qualities of the transistors used.

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