Two - way trigger diode, also known as two - end ac device (DIAC), and two - way thyristor at the same time.Because of its simple structure and low price, it is often used to trigger the bidirectional thyristor, and can also constitute overvoltage protection circuits.Construction, symbol and equivalent circuit of a bidirectional trigger diode.

Also commonly used in the overvoltage protection, timing, shift equal circuit, Figure 2 is the overvoltage protection circuit composed of bidirectional trigger diode and bidirectional thyristor.When the transient voltage exceeds the DIAC and Ubo, the DIAC quickly conducts and triggers the bidirectional thyristor to also conduct, so that the following load is protected from overvoltage damage.