triode alternating current switch (component) (TRIAC)
A TRIAC (Triode Alternating Current Switch) is an electronic component that corresponds to a parallel connection of two thyristors, one of which, however, is connected in the opposite direction. With such an arrangement both half waves of an alternating voltage can be switched.
The triac, which has two anodes and only one control electrode, provides the two required firing thyristor paths in its internal circuitry, allowing it to be switched to the low-resistance state for both half-waves of an AC voltage from a current or voltage pulse. This state is maintained until the holding voltage of the anode is undershot and the triac switches back to the high impedance state.
Triac circuits are used in dimmers, motor controls and controls for alternating current.
Current and voltage ratings for triacs are about 50 amps and several hundred volts, up to 800 V.