A TRIAC can conduct in both the directions. The conduction of a triac is initiated by injecting a current pulse into the gate terminal. The gate loses control over the conduction once TRIAC is turned ON. The TRIAC turns *** only when the current through the main terminals becomes zero.
The three terminals of TRIAC are marked MT, (Main terminal 1), MT2 (Main terminal 2) and the gate G. As TRIAC is a bidirectional device and can have its terminals at various combinations of positive and negative voltages, there are four possible electrons potential combinations, as given below:
MT2 positive with respect to MT1, G positive with respect to MT1.
MT2 positive with respect to MT1, G negative with respect to MT1.
MT2 negative with respect to MT1, G negative with respect to MT1.
MT2 negative with respect to MT1, G positive with respect to MT1.
In trigger mode-1, the gate current IG, flows mainly through P2N2 junction like an ordinary thyristor. When the gate current has injected sufficient charge into P2 layer, the TRIAC starts conducting through the P1, N1, P2, N2, layers like an ordinary thyristor.
In trigger mode-3, the gate current IG forward biases the P2 P3 junction and large number of electrons are introduced in the P2 region by NrFinally the structure P2 N1, P1, N4 turns on completely.
