Mike Hord wrote:
> I'd say your simplest solution is to use a BJT with a pot connected
> to it.

Simple in components maybe, but not so simple when you figure out how to
deal with the large wasted power that turns into heat.

I think the best answer is to use PWM and a switch that it either full on or
full off most of the time.  That minimizes the power dissipation and
shouldn't require a heat sink.  Since you are just driving LEBs (Light
Emitting Bulbs ;-) ), the switching frequency can be quite low.  How about a
10Kohm pot driving the A/D input of a 12F675, which does software PWM to
control the switching element.  I like the IRFU3706 FET in this application.
The gate can be driven directly from a PIC pin, source to ground, drain to
low side of LEBs.  These FETs can withstand up to 20V, have only 11mOhms ON
resistance with 4.5V gate drive, and cost well under a dollar.

With software PWM at about 200Hz you should get plenty of resolution.  I bet
you won't be able to notice any temperature increase in the FET with a
finger.


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