Thyristors are four-layer semiconductor devices, also known as a silicon controlled rectifier (SCR) It is like a fast static switch and is good for controlling large amounts of power, they can also control the speed of DC motors.
Thyristors usually consist of three electrodes: an anode (positive terminal), Cathode (negative terminal) and a gate. (You can also get thyristors with two or four leads). The gate is the main control terminal while the main current flows between the anode and cathode Thyristors are made of N-type and P-type materials. The N-type material is formed by doping an element with electrons to increase the number of negative charge-carrying electrons. The P-type material is also produced through doping, although the resulting charge-carrying electrons are positively charged. By alternating layers of P and N-type material, a semiconductor thyristor device is formed. Thyristors are used to create a latching circuit. Thyristors can be turned on using the gate. It then turns off when the voltage across the anode-cathode drops back down to zero.
Thyristors are commonly found in many everyday applications such as: