TRIAC

A TRIAC (triode for alternating current), is a silicon semiconductor device that acts as a switch or power control unit in AC circuits. It has three electrodes that allow electrons to flow in both directions.  They are a subset to Thyristors and related to SCRs (conduct current in a single direction).

A TRIAC is triggered into conduction in both directions by a gate signal like that of an SCR. TRIACs were designed to provide a means for the development of improved AC power controls.

TRIACs are available in a variety of packaging arrangements. They can handle a wide range of current and voltage. TRIACs generally have relatively low-current capabilities compared to SCRs — they are usually limited to less than 50 A and cannot replace SCRs in high-current applications.

TRIACs are considered versatile because of their ability to operate with positive or negative voltages across their terminals. Since SCRs have a disadvantage of conducting current in only one direction, controlling low power in an AC circuit is better served with the use of a TRIAC.

TRIACs are often used in applications that require high-power switching in AC waveforms, such as: Electric fans, Dimmer switches, Motor control, Temperature or liquid level control systems, and Output controllers for electric heaters.