The following points many be noted about the triac :
(i) The triac can conduct current (of course with proper gate current) regardless of the polari- ties of the main terminals MT1 and MT2. Since there is no longer a specific anode or cathode, the main leads are referred to as MT1 and MT2.
(ii) A triac can be turned on either with a positive or negative voltage at the gate of the device.
(iii) Like the SCR, once the triac is fired into conduction, the gate loses all control. The triac can be turned off by reducing the circuit current to the value of holding current.
(iv) The main disadvantage of triacs over SCRs is that triacs have considerably lower current- handling capabilities. Most triacs are available in ratings of less than 40A at voltages up to 600V.