Bidirectional trigger diode

Bidirectional trigger diode

Bidirectional trigger diodes were developed simultaneously with bidirectional thyristors and are commonly used to trigger them.

It is a three-layer, symmetrical two terminal semiconductor device, equivalent to an NPN transistor with an open base and symmetrical emitter and collector. Its positive and negative volt ampere characteristics are completely symmetrical.

When the voltage across the device is less than the forward transition voltage Ubo, it exhibits a high resistance state; When U>Ubo, it enters the negative resistance region. Similarly, when | U | exceeds the reverse transition voltage | Ubr |, the transistor can also enter the negative resistance region.

The symmetry of the transition voltage is represented by △ Ub

△Ub=Ubo-|Ubr|

The general requirement is △ Ub<2U. The withstand voltage value Ubo of bidirectional trigger diodes can be roughly divided into three levels:

20-60V, 100-150V, 200-250V.

In practical applications, in addition to selecting an appropriate transition voltage Ubo according to the requirements of the circuit, a bidirectional trigger diode with a small transition current Ibo and a small transition voltage deviation △ Ub should also be selected.

Bidirectional trigger diodes are not only used to trigger bidirectional thyristors, but also commonly used in circuits such as overvoltage protection, timing, and phase shifting.