Disc thyristor

Semikron Silicon Controlled Rectifier (SCR) or thyristor is a unidirectional semiconductor device made of silicon. This device is the solid state equivalent of thyratron and hence it is also referred to as thyristor or thyroid transistor. Basically, SCR is a three-terminal, four-layer semiconductor device consisting of alternate layers of p-type and n-type material.

When the anode current becomes zero, the SCR stops conducting and blocks the reverse voltage. SCRs are used in switching circuits, DC motor drives, AC.