Re: Dimmers

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: dhmccauley-at-spacecatlighting-dot-com 

A modern day dimmer is simply a triac, a few capacitors, and a variable
resistor which is the dimmer knob.
The capacitor is connected across the gate of the TRIAC to circuit neutral.
The variable potentiometer is connected in series with the hot AC line and
this capacitor.  During each cycle,
the capacitor charges up at a rate specified by the limiting resistor
(potentiometer).  When the capacitor voltage reaches the TRIAC's "ON"
threshold, the TRIAC conducts, and for the
remainder of the sine wave, the output is "ON" and follows the voltage of
the original AC sinewave.  Since a TRIAC is a latching device, the output
stays "ON" until the next zero crossing
and the process repeats.

Dan