What about using PWM to drive a transistor, create a voltage you can
control, and feed that to the ADJ pin?

Don't forget a feedback loop!

-Randy Glenn

Measure twice, cut once, curse, discard. Repeat.
=================================================
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           http://picxpert.dyndns.org
    Not that the site works yet, of course...
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-----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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