[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Original poster: "Daniel Barrett" <dbarrett1-at-austin.rr-dot-com>
I Agree completely- I meant that the *leading* edge of the pulse is
modified. The trailing edge is always the zero crossing of the AC sine
waveform. So the pulse begins at 0-90 degrees on the positive half cycle and
180-270 degrees for the negative half cycle, depending on the knob setting.
Sent: Monday, November 24, 2003 9:32 PM
To: Tesla list
Subject: Re: Dimmers
> 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.