You don't really need the '317. Use the standard 'series-pass transistor'
regulator, except substitute Vref with some form of D/A (low-pass filtered
PWM from PIC, or built-in DAC). You will want to add some gain (get a dual
op-amp) to get greater output range, of course.


Phil Eisermann
Electronics Engineer
The Ridge Tool Company
(440)329-4680


>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of James Burkart
> Sent: Thursday, November 22, 2001 5:04 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PICLIST] [OT]: Digitally-controlled variable
> voltage regulator
>
>
> Hey All,
>
>         I am trying to construct a powersupply that will be
> controlled by a
> pic. I
> have decided to us the good'ol LM317 as the regulator. I
> figure that I can
> use a D/A converter to allow a PIC to control the biasing of
> a mosfet, used
> as a variable resistor, to adjust the voltage. Another way I
> figure is to
> use a digital potentiometer, only problem is that no greater
> than 5 volts
> can be applied to any one pin or pass more than 1 or 2 mA.
> Anyone got any
> ideas? Am I making this harder than it should be? How do
> people like HP do
> it? (I know HP power-supplies cost an arm and a leg...)
>
>         I am trying to get 0.1V resolution on the output.
>
> James Burkart
> jamesburkart@yahoo.com
>
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