Haven't paid too much attention to this thread, but Olin's comments tweaked
a memory of something I played with at one time - a voltage regulator
controlled by a Basic Stamp.

Originally I tried a purely software regulator - I used a serial D to A
chip driving the pass transistor, and an A to D chip reading the o/p
voltage. It actually worked quite well, although it's transient response
was lousy since the Stamp was a slow processor. Using a faster PIC like an
877 would work better.

But then I realized I didn't need to have the processor run the control
loop - the processor just needed to supply the reference voltage for a
traditional regulator. Rather than use an LM317 or the like, I used a
simple op-amp (LF411) as the error amp driving the pass transistor. One of
the op amp inputs was driven from the DtoA converter, the other was the
feedback. This worked like a charm.

I had a small serial DAC to use, but you could use the PWM output and
filter it.

The advantage of this scheme over the idea of trying to control an LM317 is
that the o/p voltage of the regulator is the same as the DtoA output
voltage - no strange calculations are needed to determine what the o/p
voltage would be.

Larry

At 08:00 AM 11/3/2002 -0500, you wrote:
>> Yes, the adjuster pin for the 317 has only a few uA, but the switch
>> application is for the actual output from the regulator, which will be
>going
>> up to 1.5A. I mentioned the adjustor pin because I needed advice on
>> controlling the resistance digitally, hence a digital pot. Will the
>IRFP260N
>> act as a simple switch with +5V = on and 0V = off?
>
>What are you trying to accomplish overall?  An adjustable voltage source?
>If so, there are probably easier means than trying to tweak the adjust input
>of an adjustable regulator with a digital pot.
>
>
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Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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