# Triac based dimmer

#### dougtheflyboy

Joined Mar 5, 2008
7
I have a triac based dimmer it is clipping the sine wave a bit above the zero point what can be done to get it to clip right at the zero point of the sine wave?

#### Audioguru

Joined Dec 20, 2007
11,249
Triac dimmers for the mains don't clip. They use a form of pulse-width-modulation to dim. The PWM delays the triac from turning on each half-cycle to dim the light. Then it turns on late in the half-cycle and the average power in the light is low. When the AC voltage passes through zero volts then the current in the light is low and the triac turns off.

When the dim setting is high then the triac turns on early each half-cycle so the light gets almost full power.

#### thingmaker3

Joined May 16, 2005
5,084