A TRIAC (triode for alternating current, also known as bidirectional triode thyristor or a bilateral triode thyristor) is a silicon semiconductor component with three terminals or legs that allow current to flow in either direction when triggered. TRIACs are a subset of thyristors (read more in our thyristor guide) and are similar to SCRs (silicon controlled rectifiers). However, unlike SCRs and other thyristors, which are unidirectional, the TRIAC is able to control current over both halves of the sine wave, making TRIACs bidirectional. A TRIAC is a 4-layer silicon component that is PNPN in the positive direction and NPNP in the negative direction. The devices come in panel mount, surface mount, and through-hole mounting options in various package types to suit a wide variety of electronics applications and circuits.RS have a curated range of TRIACs from a multitude of trusted brands, including Littelfuse, STMicroelectronics, WeEn Semiconductors Co., and many more.

How does a TRIAC work?

In basic terms, a TRIAC is a low-to-medium power semi-latching solid-state switch. The device acts like two standard thyristors inversely connected in parallel or back to back. To activate the component a voltage needs to be applied to the gate terminal, and TRIACs can be triggered by either negative or positive voltages, whereas SCRs require a positive voltage. Once the gate current is triggered, a TRIAC will continue to conduct even if the supply to the gate is removed.

On a TRIAC symbol, there are three terminals. These terminals are:

MT1 Anode 1 (Main Terminal 1)
MT2 Anode 2 (Main Terminal 2)
Gate Terminal

You can learn more about how TRIACs work in our guide.

What are TRIACs used for?

TRIACs are widely used for switching and power control of AC systems. TRIACS are particularly useful in applications such as lighting dimmer switches, as they enable the utilisation of each half-cycle of the AC wave. The solid-state device can be used in a circuit as a simple on-off device in a wide range of electronic applications. Some of the more common areas are:

Temperature control
Liquid level control
Dimmers for domestic lighting
Small motor control
Speed control for electric fans