TRIAC – Symbol, Construction, Working with Application Circuits
A TRIACs can be formed by connecting two equivalent SCRs in inverse parallel to one another and the gates of the two SCR are connected together to form a single gate. If you are new to DIACs as well then you can read the DIAC Introduction Article to know more about it. The Symbol of the TRIAC will be like the image below, it has three terminals Main Terminal 1 (MT1), Main Terminal 2 (MT2) and Gate (G).
The MT1 and MT 2 are also called as Anode 1 and Anode 2. The TRIAC can be included in a circuit in a way that the current is flowing from either MT1 to MT2 or MT2 to MT1, there will not be any current until we inject a gate current pulse at G.
TRIAC Construction
The below shows the structure of the TRIAC, it is a four-layer device that consists of six doping regions. The gate terminal is designed in a way to have ohmic contact with both N and P regions, which helps the device to get triggered with both positive and negative polarities.
Although TRIAC is a bidirectional device, everyone prefers to specify voltage and current using MT1 as the reference in order to reduce confusion.
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TRIAC – Symbol, Construction, Working with Application Circuits
The word TRIAC can be expanded as a TRIode for Alternating Current. While other power electronic switches like MOSFET, IGBT, etc are used for switching/controlling DC power, the TRIAC is used to control AC power because once turned on TRIAC can conduct in both the direction allowing AC voltage to passes completely in both the positive and negative cycle.
The TRIAC is a three-terminal semiconductor switching device that is used for controlling current flow in a circuit. It is one of the most important members of the thyristor family; it is a bidirectional device that can pass the current in both forward and reverse direction, which means that they can conduct in both the conditions of the gate signal, positive and negative.
TRIAC Symbol
A TRIACs can be formed by connecting two equivalent SCRs in inverse parallel to one another and the gates of the two SCR are connected together to form a single gate. If you are new to DIACs as well then you can read the DIAC Introduction Article to know more about it. The Symbol of the TRIAC will be like the image below, it has three terminals Main Terminal 1 (MT1), Main Terminal 2 (MT2) and Gate (G).
The MT1 and MT 2 are also called as Anode 1 and Anode 2. The TRIAC can be included in a circuit in a way that the current is flowing from either MT1 to MT2 or MT2 to MT1, there will not be any current until we inject a gate current pulse at G.
TRIAC Construction
The below shows the structure of the TRIAC, it is a four-layer device that consists of six doping regions. The gate terminal is designed in a way to have ohmic contact with both N and P regions, which helps the device to get triggered with both positive and negative polarities.
Although TRIAC is a bidirectional device, everyone prefers to specify voltage and current using MT1 as the reference in order to reduce confusion.
TRIAC Working Principle and Operation
TRIAC can go to conduction state if the applied voltage is equal to the breakdown voltage, but the most preferred way of turning on a TRIAC is by providing a gate pulse, either positive or negative. If the gate current is high, a very small amount of voltage is enough to turn on the TRIAC. As the TRIAC is bidirectional and has an ability to get turned on with both the polarities to the gate pulse it can operate in four different types of modes of operation
1.MT2 is positive with respect to MT1 with a gate polarity positive with respect to MT1.
2.MT2 is positive with respect to MT1 with a gate polarity negative with respect to MT1.
3. MT2 is negative with respect to MT1 with a gate polarity negative with respect to MT1.
4. MT2 is negative with respect to MT1 with a gate polarity positive with respect to MT1.
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