Thyristor

A thyristor is a solid-state semiconductor used to control the flow of electricity. It is comprised of four alternating layers of p-type and n-type material. P-type material contains "positive" charge carriers (holes), while n-type material contains extra electrons. The layered structure allows a thyristor to function as a powerful switch for controlling large AC currents.

Thyristors have three terminals: the anode and cathode, which carry the main current, and the gate, a small control input (see below). A brief signal at the gate turns the device on. The thyristor stays on until the current flowing between the anode and cathode naturally falls to zero.

Thyristors also support phase-angle control, which lets a circuit deliver only part of each AC cycle. This is how some light dimmers work, where delaying conduction reduces brightness.

Where thyristors are used:

• AC power control - household and industrial light dimmers, heater controls, motor speed controllers, power regulators
• High-voltage and high-current switching - welding equipment, large industrial drives, and heavy-duty rectifiers
• Protection circuits - surge protection and "crowbar" circuits that shut down power during overvoltage events

Thyristors are generally not found in computer components like CPUs, RAM, and SSDs. These devices operate at low power, require components that switch very quickly, and turn off by control signal. Modern digital circuits instead rely on MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and other fast semiconductor technologies.