A thyristor is a solid state semiconductor device with four layers of alternating P and N type materials. It acts exclusively as a bistable switch, conducting when the gate receives a current trigger, and continuing to conduct while the voltage across the device is not reversed.
A three lead thyristor is designed to control the larger current of its two leads by combining that current with the smaller current of its other lead, known as its control lead. In contrast, a two lead thyristor is designed to switch on if the potential difference between its leads is sufficiently large.
The thyristor is a four-layered, three terminal semiconductor device, with each layer consisting of alternately N type or P type material, for example PNPN.
The main terminals, labelled anode and cathode, are across all four layers. The control terminal, called the gate, is attached to P type material near the cathode. The operation of a thyristor can be understood in terms of a pair of tightly coupled bipolar junction transistors, arranged to cause a self-latching action.
Thyristor has three states,
- Reverse blocking mode
- Forward blocking mode
- Forword conductiong mode