Thread: Versions of triacs are available

More and more version of triacs are available nowadays to make the power control circuits run perfectlyExamples are Alternistors, quadracs and opto-triacs.

Alternistors. Alternistor is the trade name of a new-generation triac with improved 'turn off' (commutation). These devices are made especially for controlling highly inductive loads such as motors. Alternistors have a built-in snubber network to reduce the rate effect. These trigger in the fourth quadrant with negative voltage and positive gate current.

Quadracs. These are specially made triacs having an inbuilt diac-triac combination. This eliminates the use of an external diac, making the circuit simple.



Opto-triacs - illuminating triacs. Opto-triacs are photosensitive triacs with an inbuilt LED and semiconductor triac portion in a single package. These are available in various voltage and current ratings (MOC series). Opto-triacs can be interfaced with triac-controlled circuits so as to get total AC isolation from the remaining circuitry. The output current of the device is limited to around 100 mA and it can handle brief surge current of 400 mA to 1A.

Opto-triacs can be directly used to drive an AC load with 100mA current and 20-watt power rating (maximum). In order to drive high power devices, a slave triac should be used.

Opto-triac cannot drive heavy current loads directly. So a slave triac must be used in conjunction with the opto-triac to drive heavy loads as shown in. In the circuit, R3C1 network provides phase shift to the triac's gate and R4-C2 act as the snubber network, and hence the circuit can be..used to drive inductive and nOIl-inductive loads.