What is TRIAC?
Triac belongs to thyristor family. The triac is the most widely used device in an alternating current applications. Basically, it is a combination of two SCRs connected in anti-parallel manner. Triac can conduct in both directions positive as well as negative of an ac supply. A triac is widely used in industries for control purposes. The triac can conduct alternating current. So, it is used for ac current applications.
Construction of Triac
The triac is a three terminal, four layer bidirectional semiconductor device. The name of three terminals is MT1, MT2 and Gate(G). The same is used for the construction of triac that is used used for thyristor.
Basically, a triac consists of two SCRs connected in anti-parallel connection with a common gate.
Symbol of Triac
I-V Characteristics of Triac
As we discuss above the triac has three terminals. MT1 MT2 and Gate (G). The triac can trigger by two methods.
Firstly when input voltage level reaches at breakover voltage or exceeds the breakover voltage.
Secondly, Gate signal is applied to the triac.
The first quadrant characteristics are just like an SCR but on the other hand, the third quadrant characteristics of a triac are identical to its first quadrant. Only polarities of the main terminals (such as MT1 and MT2) change.
The Triac can be operated in both the half-cycle of an ac supply. The output of the triac can be controlled by with the help of gate current.
Applications of Triac
- It is used to control power in steps.
- It is used as a fan regulator.
- It is used to control the speed of ac motors. Triac can control the speed by adjusting the gate current.
The triac are available in different sizes and ratings. They have the capacity to handle current from 0.5A to 100A and voltages upto 2000V. The size of the device depends upon its current carrying capacity. BT 151 is an example of triac.