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Original poster: dhmccauley-at-spacecatlighting-dot-com
> Hi Jim-
> The rate doesn't change, the phase angle changes. If the dimmer is at 50%,
> the output will be off for the first 90 degrees of the of the AC waveform,
> on for the second quadrant, off for the 3rd, etc. As you vary one from
> on to full off, the firing angle becomes later in the cycle.
Thats not entirely correct either. The phase of the output of a dimmer
switch is identical to the phase of the input. A dimmer switch merely
truncates a portion of the
original AC sinewave beginning at the first zero crossing. And since the
TRIAC is a latching device, once the TRIAC is turned on and conducting, it
will remain on until
the next zero crossing at where this process will repeat.