SCR stands for Silicon Controlled Rectifier, DIAC stands for Diode for Alternating Current and TRIAC stands for Triode for Alternating Current.

An SCR is a three terminal device. It is a unidirectional switch and conducts current in only one direction. Therefore it can either control DC power or it can control forward biased half cycle of AC input in the load. It means that an SCR can only control either positive or negative half cycle of AC input.

A TRIAC is a three terminal semiconductor device. It can control both positive and negative half cycles of AC signal input and therefore it is a bidirectional switch. The forward and reverse characteristics of TRIAC is similar to forward characteristics of SCR device. Contruction of TRIAC is equivalent to two separate SCR devices connected in inverse parallel mode.

A DIAC is a two terminal component and is a bi-directional device. DIAC can be of either PNP or NPN type. A DIAC can be switched from its off state to ON state for either polarity of an applied voltage.

In this category we have listed popular and commonly used SCR, DIAC and TRIACs.