Quadrac

A QUADRAC is a special type of thyristor which combines a DIAC and a TRIAC in a single package. The DIAC is the triggering device for the TRIAC. Thyristors are four-layer (PNPN) semiconductor devices that act as switches, rectifiers or voltage regulators. When triggered, thyristors turn on and become low-resistance current paths. They remain so even after the trigger is removed, and continue until the current is reduced to a certain level (or until they are triggered off). DIACS are bi-directional diodes that switch AC voltages and trigger TRIACS or silicon-controlled rectifiers (SCRs). Except for a small leakage current, DIACS do not conduct until the breakover voltage is reached. TRIACS are three-terminal, silicon devices that function as two SCRs configured in an inverse, parallel arrangement. They provide load current during both halves of the AC supply voltage. By combining the functions of DIACS and TRIACS, QUADRACs eliminate the need to assemble discrete parts.