How is the gate terminal of a TRIAC device designed?
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.
How does a TRIAC circuit control AC power?
A triac is a three-terminal (MT1, gate, and MT2) solid-state thyristor that uses the alternative symbols in Figure 1 and acts like a pair of SCRs wired in inverse parallel and controlled via a single gate terminal. It can conduct current in either direction between its MT1 and MT2 terminals and can thus be used to directly control AC power.
What causes the TRIAC to conduct in both directions?
A small leakage current flows through the device until it is triggered by breakover voltage or gate triggering method. Hence the positive or negative pulse to the gate triggers the triac in both directions. The supply voltage at which the triac starts conducting depends on the gate current.
How many modes of operation does a TRIAC have?
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 as listed below
What is the symbol of a TRIAC circuit?
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.
What happens when a TRIAC switch is moved to position B?
If the switch is moved to position B gate current flows at every half cycle the same as before and full power is drawn by the lamp as the triac operates in modes Ι+ and ΙΙΙ–. However this time when the switch is connected to position C, the diode will prevent the triggering of the gate when MT2 is negative as the diode is reverse biased.