Thyristors can be described as the equivalent of a diode in series with an electrical switch without any moving parts. Triacs can be thought of as two Thyristors placed back to back. Triacs are electrical devices used for controlling electrical current between two terminals depending on the device being controlled. It is used to permit only a percentage of an AC signal to go through in a circuit. It is most commonly used for speed control of motors and in dimmer switches.
A Thyristor is a semiconductor, which means it uses a p-n junction. With four layers of semiconductor materials, you get an anode, a cathode and a gate terminal. It operates by allowing the current to pass through for a preset voltage on the gate terminals. It operates under several conditions.
