What Is Difference Between SCR and TRIAC?


An SCR and TRIAC are the most important semiconductor devices used in power electronics circuits.

The main reason for the difference between SCR and TRIAC is its construction, where SCR is a Unidirectional semiconductor device, but TRIAC is a Bi-Directional semiconductor device.

Following are other difference between SCR (silicon controlled rectifier) and TRIAC (triode for alternating current) :

SCR stands for "Silicon Controlled Rectifier". TRIAC stands for "Triode for Alternating Current".
SCR construction figure. TRIAC construction figure.
SCR is a three-terminal device; terminals are — Anode, Cathode, Gate. TRIAC is a three-terminal device, terminals are — MT1, MT2, Gate.
Symbol of the SCR. Symbol of the TRIAC.
The SCR conducts current in one direction only, so it is a unidirectional device. The TRIAC conducts current in both directions, so it is a bidirectional device.
It has large current capabilities and available in large ratings. It is available in smaller ratings as compared to SCR.
SCR is mainly used to control DC power. TRIAC control DC as well as AC power.
SCR can be triggered by positive gate voltage only. TRIAC can be triggered either by the positive or negative gate voltage.
In SCR only one mode of operation is possible. In TRIAC four different modes of operation are possible.
It is more reliable. It is less reliable.
An SCR needs two heat sinks. A TRIAC needs only one heat sink.
As the SCR is a Unidirectional Device, so polarity should be maintained when it connects to any circuit. As the TRIAC is a Bi-Directional Device, so it can be connected in any manner with a circuit.
SCR examples: BT169D, 25TTS12, 5P4M, BT151, etc. TRIAC examples: BT131, MAC97A, BTA24, BTA41, etc.

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