Triac Heater Control Circuit

A triac can be used to give variable ac power control by using a phase delayed switching technique in which the triac is triggered part way through each half cycle.

Triac heater control circuit.

Triac is very commonly used in places where ac power has to be controlled for example it is used in the speed regulators of ceiling fans ac bulb dimmer circuits etc. The minimum gate current required to turn on a triac is called gate triggering current igt. While designing a triac control circuit its gate triggering parameters become crucial. Triac gate triggering current igt gate triggering voltage vgt and gate latching current il.

Here we have used the triac to turn on and off an ac load through a push button. The heater control circuit works off stable 9 volt dc supply which may be derived from the mains supply using a standard ac mains adaptor 100ma at 9v or using a traditional capacitive voltage divider assembly. The standard triac and diacset up can be seen for implementing the basic switching of the triac. A triac is a high speed solid state device that can switch and control ac power in both directions of a sinusoidal waveform being a solid state device thyristors can be used to control lamps motors or heaters etc.

This heat control using thermistor and triac circuit is designed to control the temperature of a room either by using a heat source such as an electric oven heating element or by using a fan or any cooling device. You can find such power circuits elsewhere in this website. Note ca3140 ic2 is highly sensitive to electrostatic discharge esd. Let us look into a simple triac switching circuit to understand how it works practically.

When a triac is used in an electric heater driving circuit a quick blow fuse with a current rating greater than that of the heater but less than the maximum current rating of the triac provides adequate protection. How the triac diac ac controller works the set up of the circuit is pretty standard as the the wiring is very similar to the ones which are normally employed in ordinary light dimmer switch circuits. The trigger circuit is achieved using an unijuntion transistor ujt that introduces a conduction angle on the triac. Each time the triac is gated on its load current switches sharply in a few microseconds from zero to a value set by its load resistance and instantaneous supply voltage values.