Equivalent circuit of a TRIAC
with VI characteristics
Triac is designed to operate in both directions. Triac is à bidirectional thyristors like two SCRs connected anti parallel. A common gate terminal controls both. Thus triac is called fill wave device. It has three terminals MT1(main terminal 1) and MT2(main terminal 2) and a common gate terminal.
VI characteristics of triac:
As mentioned earlier triac can operated in both directions and gate current controls it's firing. I have attached a current source at the gate terminal to congeal the gate current. As the gate current increases, the required forword breakover voltage in both directions decrease. Similarly when triac is fired the voltage drop across triac becomes very small and gate losses it's control once it is fired.
Applications: 1)AC power control
2) Fan regulator circuit
3) Light dimmer
