|> How can a TRIAC dimmers employ zero crossover switching ?
| both triac dimmers and solid state relays should employ zero crossover
| switching (zero threshold detection).
| this insures the "glitch" at the zero point is minimized or eliminated.
I also don't want the flicker that would be implied by only switching
at the zero crossover.
| here is a patent for one http://www.freepatentsonline.com/5734289.html
| granted that as dimming is engaged, the waveform becomes non-sinusoidal.
It's the long rise or fall involved in switching either in or out at
a designated point determined by the amount of time averaged current
to let through that is the problem.
One method of solving this would be to chop up the waveform at a rate
of 61.44 kHz with varying widths that approximate a sine wave times
the desired output voltage or current, and smooth the end result back
out to near sine wave with a capacitor or inductor.
Squeezing all that into a 1-gang box AND doing it in SERIES with the
light could pose an interesting challenge. I assume it is difficult,
but I asked around just in case one of the brighter engineers around
actually has employment in the right job.
|> A triac dimmer in order to operate needs to turn the triac
|> on in the middle of the mains phase to do dimming (and then
|> keep conducting to next zero crossing). RFI/EMI filters can
|> reduct the noise caused by the quitc turn on.
|> There are dimmers based on other semicondictors (power FETs etc.)
|> that turn on ath the zero crossover and then more or less
|> "slowly" turn off in the middle of the mains phase as needed.
|> When properly implemented this type of dimmers cause less
|> noise to mains then the old triac dimmers and need less filtering.
| apparently the problem is noisy lamps... maybe he could surround the bulb
| with Sonex :) (just kiddin')
I've not yet done any of the math involved, and need to get some numbers
to do the math anyway, but I might consider somehow wiring in a ballast
intended for fluorescent just to get an inductor in series, and use a
double throw switch to go one way for full and the other way for lower.
Then I have to figure out level of low I really want out of it and hope
the hum from the ballast isn't an issue (but it might be).
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
Click to see the full signature.