Hi Josh

Yes, a MOSFET main switch is an easy way to do this (compared to a
bipolar) but for PWM control you are going to need someting to drive
the fet. You can either roll your own or use a driver chip to do it
for you. Depending on he frequency of operation, an IGBT may be
another option for the main switch - but again it will need a good
driver.

For a one off / limited production project I'd suggest a driver chip.

You'll really need to use PWM to control the brightness, otherwise you
need to be able to dissipate the excess heat somewhere. It's likely to
be in the 180W area for a linear controller.

One thing to watch with incandescent lamps is that the cold current
can be 10x what you'd otherwise expect. For your 250W load at 24V the
current will be around 10.4 A when  hot - it could be approaching 100
A as a turn-on surge when cold.. This means that your MOSFET will have
to be able to handle this, and the driver circuit must be able to
provide a useful amount of drive current to counter the miller
feedback effect.

RP

2009/11/5 Josh Koffman <joshybear@gmail.com>:
> Hi all. I might be called on to help out with a project. The part I'm
> most unsure about is that the intensity of a 24V 250W light bulb will
> need to be controlled, preferably by a PIC. It's being supplied by a
> 24V battery.
>
> =A0I'd love to be able to find a compact, ready made module that would
> do this part for me. Digital (ie serial data, etc) control would be
> ideal, but analog might be possible. Alternatively I could use the CCP
> module to generate some PWM, but I'd need a driver. The reason I'd
> like a module is that in the event of a problem
 it would be easy to
> swap out. I've done some searching and what I'm finding are a ton of
> smaller modules meant for dimming LEDs.
>
> Alternatively I could use PWM and some sort of home built driver. The
> circuit here: http://www.solorb.com/elect/solarcirc/pwm1/ suggests the
> use of a FET. Having never controlled this large a DC load before, I
> have no idea if this is a good or bad idea. Any thoughts?
>
> Thanks for the help!
>
> Josh
> --
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> completely foolproof is to underestimate the ingenuity of complete
> fools.
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