Well a straightforward way to do this is a PIC based power supply.  I
built some with the following rough outline:

Slew controls (two buttons, one up, one down)
Power up at 1.2 volts (about as low as it will go anyway
Range 1.2 to 24 volts at 1 amp
User interface consists of a digital voltmeter module
PIC checks the output voltage via a resistor divider and an RC filter
through analog input
PIC drives a series pass transistor at regular intervals  - on a timer
at about 20KHz the PIC decides if the output is too high or too low and
turns the pass transistor on or off.

Current regulation is crude and simple.  The PIC is powered from the same
supply as the power supply.  If you short it out, you short out the PIC
and it reboots and turns off the current.  Crude, Rude, and short proof,
so far meets my needs.  I was going to build in a current foldback feature
when I accidentally discovered that this works just fine.  If I was going
to sell this I would of course include current foldback, but this was a
quick one-off bench supply to replace the other one that fried.

PIC is on a simple 7805 regulator, the rest of the supply is on a 24V DC
power supply.  The whole thing is in a plastic box from radio shack and
took an afternoon to put together.  I added a dedicated 5V supply from a
simple 7805 just for kicks.

I've always built my bench power supply, partly because it galls me to pay
$200 or $300 for one that doesn't regulate any better than one I can build
out of spare parts.


-- Lawrence Lile





John Waters <john_fm_waters@HOTMAIL.COM>
Sent by: pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>
06/25/2004 12:38 AM
Please respond to pic microcontroller discussion list


        To:     PICLIST@MITVMA.MIT.EDU
        cc:
        Subject:        [EE]: microcontroller based variable voltage regulation, how?


Hi All,

I want to use my car battery to provide a range of variable d.c. from
0-12V,
but a standard regulator circuit doesn't fulfill the requirement, as I
want
the output voltage to be adjustable by software through a microcontroller,
could someone suggest how to do that?

Thanks in advance!

John

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