What Is a TRIAC?
A TRIAC, unlike a thyristor (SCR), is a power switch that can conduct in both directions. Because it can control both the positive and negative half of the AC signal, it's indispensable for AC power control.
How Does It Work?
It can be thought of as two SCRs connected in inverse-parallel. When a trigger pulse arrives at the gate it starts conducting and turns off at the current zero-crossing. It triggers both directions with a single gate.
Difference From an SCR
An SCR passes current in only one direction (half-wave); a TRIAC passes it in both directions (full-wave). So it controls the power of AC loads more efficiently and symmetrically.
| Property | SCR | TRIAC |
|---|---|---|
| Direction | Unidirectional | Bidirectional |
| AC control | Half-wave | Full-wave |
Phase Control and Dimmer
A TRIAC adjusts the power to the load by triggering late in each AC half-cycle (phase control). Light dimming and motor speed control work this way; a DIAC is often used for triggering.
Where Is It Used?
Lamp dimmers, fan/motor speed control, heater power adjustment, solid-state switching in place of an AC relay.
Common Mistakes
- Skipping the snubber: with inductive loads dV/dt causes unwanted triggering; an RC snubber is needed.
- Zero-cross: zero-cross switching can be preferred to reduce noise.
- Trigger current: insufficient gate current gives unstable conduction.
Frequently Asked Questions
Does a TRIAC control DC?+
Why does a dimmer use a TRIAC?+
Search parts related to "What Is a TRIAC?"
Find the right part by comparing price, stock and distributors.