TRIAC

TRIAC

It is a bidirectional device that can pass the current in both forward and reverse biased conditions and hence it is an AC control device. The triac is equivalent to two back to back thyristors connected with one gate terminal as shown in the figure. TRI means that the device consisting of three terminals and AC means that it controls the AC power (i.e conduction takes place on both positive and negative half cycles and TRI + AC = TRIAC). Due to the bidirectional control of AC, triacs are used as AC power[1] controllers, fan controllers, heater controllers, triggering devices for SCRs, three position static switch, light dimmers, etc.

V-I Characteristics of TRIAC

The TRIAC function like a two thyristors connected in anti-parallel and hence the VI characteristics of triac lies in the 1st and 3rd quadrants and is similar to the VI characteristics of thyristors.
In summary, if MT2 is positive with respect to MT1, the triac can be turned on by applying a positive gate signal between gate and MT1 and it represents the V-I characteristics of the first quadrant. Similarly, if MT1 is positive with respect to MT2, the triac can be turned on by applying a negative gate signal between gate and MT1 and it represents the V-I characteristics of the third quadrant. The explanation of the nature of the curves is similar to that described previously in the thyristor.

MERITS OF TRIAC

1) It turns off when a voltage is reduced to zero.

2)A single gate controls conduction in both positive and negative cycle.

3)Triac with higher voltage ratings are available easily on the market.

DEMERITS OF TRIAC

1) It has very high switching delay.

2). It is not suitable for DC power applications.

REFRENCES

Electronicshub. TRIAC/. n.d. <http://www.electronicshub.org>.