What is TRIAC-TRIode for AC?

TRIAC-TRIode for AC

TRIAC is used to control AC voltage,  in applications like electric range heating controls, light dimmers, and small motors etc. TRIAC is a bidirectional device.

·  Like the SCR, the TRIAC latches after triggering and turns off when the current is below the holding current(I_H), which happens at the end of each alteration.

•The TRIAC belongs to the thyristor family.It can conduct in both directions.

•     Thus a TRIAC is similar to two back to back (anti parallel) connected thyristors but with only three terminals.

•     The three terminals are marked as MT1 (Main Terminal 1), MT2 (Main Terminal 2) and the gate terminal by G.

•When the voltage on the MT₁ terminal is positive with respect to MT₂, a gate current pulse will cause the left SCR to conduct. On reversing the anode voltages, the gate current pulse  causes the  2nd (right) SCR to conduct. 

V-I Characteristics of TRIAC

•In TRIAC two SCRs are connected in anti parallel.

•Therefore, the V-I characteristics of TRIAC in the 1^st and 3^rd quadrant, will be similar to the forward characteristics of a thyristors.

•TRIAC conducts in both direction hence it is a bidirectional device and can have its terminals at various combinations of positive and negative voltages.
There are four possible electrode potential combinations as given below :-

–  MT2 and Gate terminal are positive with respect to MT1.

–  MT2 positive with respect to MT1 but Gate terminal is negative with respect to MT1.

–  MT2 and Gate terminal are negative  with respect to MT1.

–MT2 negative with respect to MT1 but Gate terminal is positive with respect to MT1.

VI-Charecteristics of TRIAC