The term 'quadrac'  refers to a special kind of thyristor developed and manufactured by Teccor, which is basically a triac that has a triggering diac at its gate. 

The quadrac is therefore a convenient alternative for someone who intends to build a circuit that uses a discrete triac whose gate needs to be triggered by a discrete diac. The quadrac behaves like a bidirectional AC switch that is triggered by a voltage that exceeds the breakdown voltage of the diac in either polarity.

Applications of the quadrac primarily pertain to AC switching and AC phase control, examples of which include AC motor speed control,  temperature control modulation, and lighting systems control.

Typical quadracs can handle currents ranging from 4 to 15 amperes and voltages ranging from 200 V to 600 V.

Figure 1.  Photo of a quadrac (left) and the symbol for a quadrac (right)

See Also:   Triac;  Diac;  Active Components;  More Articles