TRIAC Characteristics in tamil

Characteristics of a Triac
The triac characteristics is similar to SCR but it is applicable to both positive and negative triac voltages.

First Quadrant Operation of Triac
Voltage at terminal MT2 is positive with respect to terminal MT1 and gate voltage is also positive with respect to first terminal.

Second Quadrant Operation of Triac
Voltage at terminal 2 is positive with respect to terminal 1 and gate voltage is negative with respect to terminal 1.

Third Quadrant Operation of Triac
Voltage of terminal 1 is positive with respect to terminal 2 and the gate voltage is negative.

Fourth Quadrant Operation of Triac
Voltage of terminal 2 is negative with respect to terminal 1 and gate voltage is positive.

When the device gets turned on, a heavy current flows through it which may damage the device, hence in order to limit the current a current limiting resistorshould be connected externally to it. By applying proper gate signal, firing angle of the device may be controlled. The gate triggering circuits should be used for proper gate triggering. We can use diac for triggering the gate pulse. For firing of the device with proper firing angle, a gate pulse may be applied up to a duration of 35 micro seconds.

Advantages of Triac
It can be triggered with positive or negative polarity of gate pulses.
It requires only a single heat sink of slightly larger size, whereas for SCR, two heat sinks should be required of smaller size.
It requires single fuse for protection.
A safe breakdown in either direction is possible but for SCR protection should be given with parallel diode.

Disadvantages of Triac
They are not much reliable compared to SCR.

It has (dv/dt) rating lower than SCR.

Lower ratings are available compared to SCR.

We need to be careful about the triggering circuit as it can be triggered in either direction.

Uses of Triac
They are used in control circuits.
It is used in High power lamp switching.
It is used in AC power control.

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