Thyristor: principle of operation. Thyristor classification

The principle of operation of thyristors is based on the basis of a semiconductor crystal (electronic key) with three or more pn junctions. The element has two stable positions: a state of low or high conductivity. Under the influence of a control signal, the device is brought into a conductive effect. In other words, it turns on the circuit. For its activation, it is necessary to create suitable conditions that ensure the reduction of the main current to zero.

Description

On the fingers, the thyristor operation principle can be explained as follows: the keys conduct current exclusively in the forward direction. And in the closed position, it also withstands reverse voltage. The structure of the device has four layers and three conclusions:

1. A (anode).
2. K (cathode).
3. U (control electrode).

Powerful electronic keys are equipped with various ampere and voltage parameters that affect the performance and condition of the element. Thyristors are capable of functioning at values ​​up to five thousand volts, 5000 A, if the frequency does not exceed 1000 Hz.

Commutation

The principle of operation of the thyristor allows it to work in two switching ranges:

1. Natural switching. It occurs when the device operates in an alternating current circuit. This process occurs when the current decreases to the zero position.
2. Forced switching. This process can be carried out in several ways, depending on the scheme used by the developer.

The standard form of forced switching is to connect a charged capacitor. In such a circuit, current fluctuations occur during loading.

Ways to turn off and on

The principle of operation of the thyristor allows you to use several methods of forced switching. Among them:

1. Using a capacitor with reverse polarity . It can be activated in the circuit using an auxiliary element. Then a discharge is made to the main thyristor, as a result of which the current directed towards the forward voltage will ensure its decrease up to the zero position. The device turns off, due to its characteristic features.
2. Connection of LC chains . They discharge with vibrations, providing a meeting of the working and discharge current. After balancing, the thyristor turns off. In the final phase, the current from the oscillatory circuit moves through the thyristor to a semiconductor diode. During this process, a certain voltage is applied to the device, equal in magnitude to the similar indicator on the diode.

The principle of operation of the thyristor in DC circuits

The standard device is activated by applying current to the test terminal. It must be positive with respect to the cathode. The flow of transient flows depends on the type of load, its amplitude and the rate of injection of the pulse current. In addition, the temperature regime of the semiconductor crystal, as well as the applied voltage in the thyristor circuits, is important. The circuit parameters directly depend on the type of semiconductor used.

In the thyristor placement circuit, an intensive increase in the voltage increase rate is not allowed. A value is achieved that ensures spontaneous deactivation of the device, even without a signal in the control system. At the same time, a high indicator of the characteristic of the control unit must be simultaneously supported.

Variable circuit: thyristor operation principle

The principle of operation of the element in this case allows the following actions:

1. Activate or break the circuit with an active or resistive load.
2. Correct the working and average indicator of the current giving the load. This is possible by adjusting the peak of control feed.
3. Since thyristors conduct current in one direction, the use of counter-parallel connection in alternating circuits will be required. The operating and average voltage values ​​may vary due to a change in the supply signal to the device. In any case, the power of the element must correspond to the presented parameters.

Phase and pulse width modulation

Thyristor switching methods also include phase control. In this case, the load is adjusted by adjusting the phase angles. Artificial commutation is available through special circuits or fully lockable analogs. In this way, thyristors are mainly manufactured for chargers with the ability to adjust the current strength according to the charge of the battery.

Pulse Width Modulation (PWM) works as follows:

• When the thyristor is opened, a control signal is given.
• In this case, the transitions are open, and a certain voltage appears on the load part.
• During the closing period of the element, the control signal is not broadcast, which ensures a stop of the current supply through the device.

It is worth noting that during phase control, the current curve is not sinusoidal; the voltage waveform is transformed. At the same time, it is planned to disrupt the functioning of consuming elements that are susceptible to high frequency interference. Change the value to the required indicator allows a special regulator.

Varieties

There are several types of thyristors (the principle of operation for "dummies" is discussed above). They are used in chargers, switches, volume controls. The following modifications are distinguished:

• Optothyristor . Uses a light-sensitive semiconductor in the circuit. The device is controlled by applying a luminous flux.
• Thyristor diode . Equipped with an active parallel connected diode.
• Dinistor . It can transform into full conduction mode (if the nominal voltage indicator is exceeded).
• Triac Consists of a pair of thyristors having a counter parallel connection.
• Inverter thyristor . It features a high commutative speed of up to 50 μs.
• Elements with a field effect transistor . They operate as metal oxide semiconductors.

Specifications

Consider the parameters and principle of operation of the KU202N thyristor:

• The maximum voltage is 400 V.
• Constant / repeating pulse current - 30/10 A.
• The voltage in open mode is 1.5 V.
• The operating DC current is 4 mA.
• The unlocking current at the control unit is 200 mA.
• The maximum increasing speed in the closed position is 5 V / μs.
• The on / off period is 10/100 μs.

The device operates according to the standard scheme for lockable thyristors. Its analogues: 1N4202, VTX32 S100, KUM202M.

Design

The four-layer configuration of thyristors distinguishes them from analogs by the complete controllability of the element. Ampere and voltage indicators for the forward direction of the current is similar to the parameters of conventional thyristors. However, the devices in question are capable of passing a significant voltage. Lock options for reverse high voltages are not provided for lockable elements. In this regard, its aggregation with a counter parallel semiconductor diode is required.

A significant drop in direct voltage is the main distinguishing feature of a lockable thyristor. To turn it off, it is necessary to supply a powerful pulse current to the control terminal. In this case, the pulse duration should be as low as possible (from 10 to 100 μs). The negative ratio with forward current is 1/5. The total difference in the limiting voltage of the device in question is 25% less than that of a conventional analog.

Finally

We have considered the classification of thyristors and their features. The following conclusion can be made: these devices are devices that are critical to the growth rates of direct voltage and current strength. For thyristors, reverse currents are characteristic, which allow you to quickly lower the value in the circuit to zero. To protect the elements, various schemes should be applied, which make it possible to protect the unit from high voltages in dynamic mode.