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Re: Singing light bulb on dimmer switch


  This is the type of technology that I was hoping was available in a fairly
small package, for home use.

  I was wondering if a simple capacitor filter would smooth the rise and
fall slope.

- David

<harold@xxxxxxxxxxxxxxx> wrote in message
> Filament singing is a common problem with phase control dimmers. I
> design phase control dimmers for theatre and television use. The amount
> of sing can be reduced by limiting the rise time when the switching
> device switches on. With triacs and SCRs, this is normally done with a
> choke in series with the device. Wall mount and other consumer dimmers
> have relatively small chokes due to the amount of space available and
> cost considerations. The choke is often a a "stick" of ferrite with
> wire wrapped around it. We use toroid cores that are considerably
> larger.
> Some professional dimmers are now using IGBTs as the switching device.
> These can be turned on more slowly, increasing risetime and limiting
> filament sing. The slow turn-on increases power dissipation in the
> device, but there are also losses in chokes used in thyristor dimmers,
> so the total losses may be equivalent. These dimmers often vary the
> rise time with heat sink temperature, speeding up the rise time as the
> unit heats up, limiting total temperature rise.
> Some IGBT dimmers also do "reverse phase control" where the lamp is
> dimmed by an "early turn off" instead of a "late turn on." Fall time
> control is used here to limit singing.
> IGBTs are considerably more complex to drive when compared with SCRs
> and triacs, so IGBT based dimmers are generally more expensive.
> There are also some "true sine" dimmers that high frequency chop the
> incoming AC, then filter out the high frequency. Due to complexity of
> the high frequency drive of the IGBTs and the requirement for a high
> power high frequency filter on each channel, these dimmers are also
> more expensive than phase control.
> As Jeff points out, Variac light dimmers (variable autotransformer)
> output a variable voltage sine wave which keeps lamps from singing. My
> high school auditorium had a dimmer system based on these. It had
> really big handles you run up and down to control the lights.
> Way way back, theatres used salt water for dimming. Electrodes would be
> dipped in and out of salt water to bring the lamps up and down. I don't
> suggest this at home!
> Harold
> http://www.dovesystems.com

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