The Diac
The diac is a special-purpose bidirectional diode. The primary function of the diac is to phase shift a triac. The operation of the diac is very similar to that of a unijunction transistor, except the diac is a “bi” or two-directional device. The diac has the ability to operate in an AC circuit while the UJT is a DC device only.
There are two schematic symbols for the diac, Figure 55–1. Either of these symbols is used in an electronic schematic to illustrate the use of a diac; therefore, you should become familiar with both.
DIAC CHARACTERISTICS
The diac is a voltage-sensitive switch that can oper- ate on either polarity, Figure 55–2. When voltage is applied to the diac, it will remain in the turned-off state until the applied voltage reaches a predetermined
