I have also been pondering this. I have a circuit for a motor speed
controller which uses an IGBT as the controlling device. This is
PWM-switched at 1.2KHz. It switches DC, but of course, there's an old
trick which works well if you don't mind having a control circuit for
which the 'ground' side is not neutral. Place the IGBT or power MOSFET
across the plus and minus side of a bridge rectifier. The AC side of the
bridge connects in series to the load. The switching element always sees
DC but the lamp then sees AC. Using PWM you could make a very fine lamp
dimmer - no 'hop on' or flicker at low brightness levels unlike triac
dimmers, but the 1.2KHz switching speed might be a problem for EMI -
does anyone know how to design an effective line filter for this - would
the same series choke design as used for a Triac dimmer work well?.

> ----------
> From:         Alan McFarland[SMTP:alanmcf@APPLIEDMAGIC.COM]
> Reply To:     pic microcontroller discussion list
> Sent:         Tuesday, December 02, 1997 3:03 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      60Hz, 120V AC PWM Routine Needed
>
> Hi--
>
> Does anyone have a circuit and some code for driving a 60 Hz,
> mains-line
> synced  PWM?  I need to create an AC dimmer for 120V incandescent
> lights
> that will  operate under PIC control.  I know it's been done, but I
> have
> yet to see a  lucid explanation of how the routine works...
>
> I've seen the appnote on the PIC12 dimmer- the one presented at the
> seminar I  attended- and it is only applicable to dimming a DC bulb
> using PWM- no 60Hz  waveform synchronization needed-- what I need to
> do is a very different animal.   Can anyone help?
>
> Thanks-- I thought I'd see if anyone can help so I don't spend
> development
> time  re-inventing the wheel!
> Alan McFarland's Applied Magic
> Custom Electronics for the Motion Picture Industry
> Lighting and Electronics for Models, Miniatures, Props & Sets
>
> http://www.appliedmagic.com
>