What Is a DIAC?
A DIAC is a bidirectional trigger element that stays an insulator until the voltage across it reaches a certain threshold (the breakover voltage), then suddenly starts conducting once the threshold is exceeded.
How Does It Work?
Normally it passes no current. When the voltage between its terminals exceeds the breakover value it suddenly becomes conductive and the voltage across it drops ("negative resistance" behavior). This sudden transition produces a sharp trigger pulse.
It's Bidirectional
Unlike a diode, a DIAC responds the same way to both polarities. So it can produce a trigger in both the positive and negative AC half-cycle.
| Property | Value |
|---|---|
| Below threshold | Insulator |
| Above threshold | Sudden conduction |
| Direction | Bidirectional |
Most Common Use: TRIAC Triggering
A DIAC is most used to trigger the gate of a TRIAC. Together with an RC circuit, it gives the TRIAC a clean and symmetrical trigger pulse in each AC half-cycle, ensuring stable dimmer operation.
Where Is It Used?
Light dimmers, motor speed control circuits, heater control and general TRIAC triggering circuits.
Common Mistakes
- Threshold mismatch: the DIAC breakover voltage must be chosen to suit the circuit.
- RC value: a wrong time constant corrupts the trigger angle and dimmer range.
- Relying on polarity: a DIAC is symmetrical, so connecting it with a direction in mind is unnecessary.
Frequently Asked Questions
What is a DIAC good for on its own?+
What's the difference between a DIAC and a diode?+
Search parts related to "What Is a DIAC?"
Find the right part by comparing price, stock and distributors.