Definition
A solid-state electronic component that acts as a switch for alternating current (AC). A triac can conduct electricity in both directions and is turned on by a small control signal applied to its gate terminal, allowing it to control the flow of AC power to a load such as a lamp, heater, or motor.
Plain English
An electronic switch that controls AC electrical current. A small signal turns it on, and it then lets full current flow through until the AC cycle naturally turns it off again.
Context Anchor
Seen in aircraft electrical and avionics maintenance discussions, especially in circuits that control AC-powered equipment, lighting, or heating elements.
Derivation
The name comes from 'TRIode for Alternating Current.' A triode is a three-terminal device, and 'AC' indicates it works with alternating current — together describing what the component is and does.
Why Pilots Care
Triacs are common failure points in cockpit lighting dimmers and certain AC-powered accessories. Knowing the term helps when reading maintenance write-ups or troubleshooting intermittent lighting and power issues.
Analogy
A triac is like a wall light switch that is operated by a small electrical signal instead of by your hand. Unlike a simple wall switch, it is built to work inside an electronic circuit.
Intuition Check
Do not think of a triac as just any electronic switch. Its key feature is that it controls AC current and can conduct in both directions.
Example Sentence 1
The instrument panel dimmer stopped working because a triac in the control circuit had failed.
Example Sentence 2
A failed triac prevented the cabin dimming system from adjusting the overhead lights during the flight.