A two-lead alternating current semiconductor that allows current to flow in both directions at a preset voltage.

A two-terminal electronic device that is specifically designed to fire in both the positive and negative directions when its applied voltage reaches a predetermined amount.

a bi-directional breakover diode; often used for triggering a triac

a full-wave or bidirectional thyristor

A two terminal bidirectional thyristor. Has a symmetrical switching mode.

A semiconductor device that can conduct current in either of two directions when properly activated. A two-terminal device whose forward and reverse characteristics of the silicon unilateral switch (SUS).

A two terminal bi-directional semiconductor device designed for triggering TRIAC s and SCR

The DIAC, or DIode for Alternating Current, is a bidirectional trigger diode that conducts current only after its breakdown voltage has been exceeded momentarily. When this occurs, the resistance of the diode abruptly decreases, leading to a sharp decrease in the voltage drop across the diode and, usually, a sharp increase in current flow through the diode. The diode remains "in conduction" until the current flow through it drops below a value characteristic for the device, called the holding current.