Best Tutorial on TRIAC

In this tutorial we are going to learn about best tutorial on TRIAC


TRIAC is three terminal devices; it conducts in either direction when turned on. It is three terminal devices with bidirectional semiconductor device which control AC power and SCR control DC power. It is mostly use in the field of power electronic of control purpose.

Symbol of TRIAC –

As per below image for symbol of TRAIC, As per below symbol can see there is three terminals device which have terminals like Terminal 1(MT1), Main Terminal 2 (MT2) and Gate (G) as shown in circuit.

Working of TRIAC Circuit –  

When the  MT1 is forward biased with respect to MT2, in cans  the current flows always  will be from MT1 to MT2. Same as it is, when the MT2 is forward biased with respect to MT1, in case the current flows from MT2 to MT1.

The above both conditions are can get conduct only when the gate is triggered with an proper  gate pulse and same like that  the SCR, TRIAC  is also turned by use appropriate current pulses at the gate terminal. If it is turned ON, then it can lose its gate control over its conduction. So that TRIAC can be turned OFF by reducing the current to zero through the main terminals.

Construction of TRIAC –

As per below image for construction of TRAIC. It has a five layer, with three terminal semiconductor devices like that MT1 is anode, MT2 is cathode terminals & the gate is G, The SCR construction can see  the gate is connected to N4 and P2  with a metallic contact and it is near to the MT1 terminal.

Here can see terminal MT1 is connected to both N2 and P2 regions, else the MT2 is connected to both N3 and P1 regions. In this construction, the terminals MT1 and MT2 connected to both P and N regions of the device and so that the polarity of applied voltage between these two terminals that can define the current flow through the layers of the TRAIC.

And when the gate open, MT2 become positive with respect to MT1 for a forward biased TRIAC. While it is operates in forward blocking mode till the voltage across the TRAIC is less than the forward break-over voltage. Same as it for a reverse biased TRAIC, MT2 is become negative with respect to MT1 with gate open. Till the voltage across the TRIAC is less than the reverse break- over voltage, means device operates in a reverse blocking mode. A TRAIC can be become conductive by either positive or negative voltage at the gate terminal.

Advantage of TRIAC –

  • It can be triggered with positive or negative polarity of gate pulse.
  • TRIAC have sufficient a single heat sink of slightly large size, whereas for SCR, two heats sinks should be required of small size.
  • It requires single fuse for protection.
  • It has safe breakdown in either direction is possible but for SCR protection should be given with parallel diode.

Disadvantage of TRIAC –

  • It is not much reliable as compared to SCR.
  • It has (dv/dt) rating lower than SCR.
  • Lower rating is available compared to SCR.
  • It has needed to be careful about the triggering circuit as it can be triggered in either direction.

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