I'm don't understand your idea 100%, yet, but from what I see, wouldn't that
limit me to a regulation between 0 and +Vcc (ie: 5V)?? The 317/337 combo I am
using lets me have 0-25 and -25 - 0 (since I am using a stepdown transformer
to 50V). I couldn't accomplish this with a DAC, could I?
Quoting Larry Bradley <lhbradley@IGS.NET>:

> 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.
> >
> >
> >*****************************************************************
> >Embed Inc, embedded system specialists in Littleton Massachusetts
> >(978) 742-9014, http://www.embedinc.com
> >
> >--
> >http://www.piclist.com hint: PICList Posts must start with ONE topic:
> >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
> >
>
> Larry Bradley
> Orleans (Ottawa), Ontario, CANADA
>
> --
> http://www.piclist.com hint: PICList Posts must start with ONE topic:
> [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads
>
>




----------------------------------------
This mail sent through www.mywaterloo.ca

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads