Triac Heater Control Circuit

The minimum gate current required to turn on a triac is called gate triggering current igt.

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. 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. You can find such power circuits elsewhere in this website. 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.

Note ca3140 ic2 is highly sensitive to electrostatic discharge esd. 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. Triac gate triggering current igt gate triggering voltage vgt and gate latching current il. The trigger circuit is achieved using an unijuntion transistor ujt that introduces a conduction angle on the triac.

Let us look into a simple triac switching circuit to understand how it works practically. Given that the load or the heater in this instance is linked in series with the triac the load also switches off and on in keeping with the triac. Here we have used the triac to turn on and off an ac load through a push button. The standard triac and diacset up can be seen for implementing the basic switching of the triac.

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. 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. 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. The moment the sine curve exceeds the above specific voltage level the diac quits carrying out and the triac is turned off.