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What is a Triac? How does a triac work?


What is a Triac?
Triacs are electronic elements that are wide utilized in AC power control applications. They are ready to switch high voltages and high levels of current, and over each elements of an AC wave form. This makes triac circuits ideal to be used in a variety of applications wherever power switching is required.
One specific use of triac circuits is in light dimmers for domestic lighting, and that they are utilized in several different power control situations together with motor control and electronic switches.
As a result of their performance, triacs tend to be used for low to medium power electronic switching applications, leaving thyristors to be used for the very heat duty AC power switching applications.
How does a triac work?
Before looking at how a triac works, it helps to have an understanding of how a thyristor works. In this way the basic concepts can be grasped for the simpler semiconductor device and then applied to a triac which is more complicated.
For the operation of the triac, it may be imagined from the circuit image that the triac consists of two thyristors in parallel however around other ways. The operation of the triac will be looked on during this fashion, though the particular operation at the semiconductor level is rather additional complicated.
Triac applications
Triacs are used in many applications. These electronic components are often used in low to medium power AC switching requirements. Where large levels of power need to be switched, two thyristors / SCRs tend to be used as they can be controlled more easily.
Nevertheless triacs are widely used in many applications:
Lighting control - especially domestic dimmmers.
Control of fans and small motors.
Electronic switches for general AC switching and control
There are naturally many other triac applications, but these are some of the most common.
In one specific application, Triacs will be included in modules known as solid state relays. Here an optical version of this semiconductor device is activated by an LED light source turning the solid state relay on according to the input signal.
Typically within solid state relays, the LED light or infrared source and the optical triac are contained within the same package, sufficient isolation being provided to withstand high voltages which may extend to hundreds of volts or possibly even more.
Solid state relays are available several forms, however those used for AC switching may use a triac.
Advantages of Triac
It may 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 a single fuse for protection.
A safe breakdown in either direction is possible except for SCR protection ought to be 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 watch out regarding the triggering circuit because it is triggered in either direction.

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