Thyristor is the abbreviation of crystal thyristor, also known as thyristor rectifier, formerly referred to as controllable silicon. In 1957, General Electric Corporation of the United States developed the world's first thyristor product and commercialized it in 1958. Thyristor is a PNPN four-layer semiconductor structure, which has three electrodes: anode, cathode and control electrode; thyristor has the characteristics of silicon rectifier devices. It can work under high voltage and high current, and its working process can be controlled. It is widely used in controllable rectifier, AC voltage regulation, contactless electronic switch, inverter and frequency conversion circuit.