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 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 Components 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

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

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Description Price Rated Average On-State Current Mounting Type Package Type Maximum Gate Trigger Current Repetitive Peak Reverse Voltage Surge Current Rating Pin Count Maximum Gate Trigger Voltage Repetitive Peak Forward Blocking Voltage Maximum Holding Current Dimensions Length Width Height
RS Stock No. 811-1098
Mfr. Part No.T1250H-6G
Each (In a Pack of 5)
12A Surface Mount D2PAK (TO-263) 50mA 600V - 3 1V - 75mA 10.28 x 9.35 x 4.6mm 10.28mm 9.35mm 4.6mm
RS Stock No. 792-0695
Mfr. Part No.BT134W-600D,115
Each (In a Pack of 20)
1A Surface Mount SOT-223 10mA 600V 11A 3+Tab 0.4V 600V 10mA 6.7 x 3.7 x 1.8mm 6.7mm 3.7mm 1.8mm
RS Stock No. 2508962580
Mfr. Part No.NTE56022
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