### Introduction

An SCR can be conducted in only one direction. So only the positive half cycle of the circuit can be controlled. But the requirement of many applications is to control both inputs of the half cycle.

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### Construction of TRIAC

When the two PNPN SCR are connected in antiparallel configuration with a common gate, then TRIAC can be found.

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### Working Principle of TRIAC

The Triac can be turned on in each half cycle of the applied voltage, when MT2, is +ve w.r.t MT1.

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### MT2 is positive and Gate G is also positive w.r.t. MT1

the junction P1 N1 P2 N2 are forward biased but the junction N1 P2 is reverse biased.

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### MT2 is positive but Gate (G) is negative

When MT2 is positive but the signal to gate terminal is negative, gate current will start flowing through Pa no junction.

### MT2 is negative but Gate (G) is positive w.r.t. MT1

When MT2 is negative w.r.t MT2, but the signal to the gate (G) is positive, then the junction N1 P1 is reverse biased. When the gate current starts to flow, the reverse biased junction N1 P1 breakdown.

### MT2 is negative and Gate (G) is also negative

When the MT2 is negative w.r.t MT1, then gate current (Ig) starts to flow from the pa na region.

### Procedure to Solve a Circuit using Norton’s Theorem

The step-by-step procedure for solving circuits using Norton’s Theorem involves removing resistances.

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### V-I Characteristics of TRIAC

the TRIAC can be conducted in two quadrants (quadrant 1 and quadrant 3) either a positive or negative gate voltage is applied.

### Applications of TRIAC

Triac applications are given below: 1. It can be extensively used in residential lamp dimmers and heat control. 2. It can also be used for speed control of small single-phase series and induction motors.

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