On Mon, 9 Oct 2006 23:19:08 -0400 TimPerry wrote: |>
|> 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
formatting link
| | 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).