At 12:21 PM 2/18/02 -0600, you wrote:
>On Mon, 18 Feb 2002, Michael Rigby-Jones wrote:
>
> > But if we are going complex, how about a bridge rectifier in series
> with the
> > lamp, and a FET or bipolar on the output of the bridge rectifier.
>
>Interesting point -- I could then use a MOSFET and PWM to start the lights
>soft, then cut 'em back to a soft glow late at night.

The triac and phase control will be more efficient, and probably cheaper,
and won't look any different.

(Two series diode losses + 1 transistor loss) > one triac loss

>  Now I realize how
>little I know about light bulbs -- these are the little 8W wedge-base
>landscape light bulbs intended for 12V operation.  Is there any problem
>using DC instead of AC, and will running them on a low brightness with PWM
>shorten their life, I wonder?

Wedge base? Ours are automotive style bayonet base (tail-lamps)
Anyway, the DC thing is pretty much a myth. If they are halogen they
should be operated at full power for a while periodically to get the
envelope temperature up. Easy to program with your PIC. ;-)

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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