Working principle of thyristor

Thyristor is the abbreviation of thyratron, and it can also be called silicon controlled rectifier, formerly referred to as silicon controlled rectifier. 1957 general electric company developed the first thyristor product in the world and commercialized it in 1958; Thyristor is a PNPN four-layer semiconductor structure with three poles: anode, cathode and grid; The working conditions of thyristor are: DC voltage is applied, and the gate has trigger current; Its derivative devices are: fast thyristor, bidirectional thyristor, reverse thyristor, light-controlled thyristor and so on. It is a high-power switching semiconductor device, which is represented by "V" and "VT" in the circuit (represented by the letter "SCR" in the old standard). Thyristors have the characteristics of silicon rectifier devices, can work under high voltage and high current conditions, and the working process is controllable. They are widely used in controllable rectification, AC voltage regulation, contactless electronic switches, inverters, frequency conversion and other electronic circuits.

Types of thyristors

Thyristors can be classified in many ways.

(1) Classification by off, on and control modes.

Thyristors can be divided into ordinary thyristors, bidirectional thyristors, reverse thyristors, GTO, BTG thyristors, temperature-controlled thyristors and light-controlled thyristors according to their turn-off, turn-on and control modes.

(II) Classification by pin and polarity

Thyristors can be divided into diode thyristors, triode thyristors and quadrupole thyristors according to pin and polarity.

(3) Classification by packaging form

Thyristors can be divided into three types according to the packaging form: metal encapsulated thyristors, plastic encapsulated thyristors and ceramic encapsulated thyristors. Among them, metal encapsulated thyristors are divided into bolt shape, flat plate shape, round shell shape, etc. Plastic encapsulated thyristors can be divided into two types: finned and finned.

(4) according to the current capacity classification

Thyristors can be divided into high power thyristors, medium power thyristors and low power thyristors according to their current capacity. Generally, high-power thyristors are mostly packaged in metal shell, while medium and small-power thyristors are mostly packaged in plastic or ceramic.

(5) Classification by turn-off speed

Thyristors can be divided into ordinary thyristors and high frequency (fast) thyristors according to their turn-off speed.

Working principle of thyristor

In the working process of thyristor T, its anode A and cathode K are connected with power supply and load to form the main circuit of thyristor, and its grid G and cathode K are connected with the device for controlling thyristor to form the thyristor control circuit.

Working conditions of thyristor:

1. When the thyristor bears the reverse anode voltage, the thyristor is in the off state no matter what voltage the gate bears.

2. When the thyristor bears the positive anode voltage, the thyristor is turned on only when the grid bears the DC voltage.

3. When the thyristor is on, as long as there is a certain positive anode voltage, the thyristor will remain on regardless of the gate voltage, that is, after the thyristor is on, the gate will lose its function.

4. When the thyristor is turned on, when the voltage (or current) of the main circuit is reduced to close to zero, the thyristor is turned off.