I have a power supply problem which I am hoping to get some good suggestions
on..... (I have lots of my own bad ideas)

I am designing a small PIC-based device for use in mobile hydraulic
machinery.  There is VERY little room on the board - the
board will be less than .85x.75 inches / 22x19 mm, and there will be a 3A
high-side (solenoid) driver along with a PIC12CE673 and a linear Hall effect
sensor in a TO-92ish package.  The board will be potted into a .25" / 6mm
thick package.

The device will be connected to anything from 10 to 26 VDC with a power
supply requirement of 20 mA @ 5 VDC.  All of the hideous automotive-type
abuse will be present; e.g. reversed battery, load dump, battery disconnect
and voltage peaks.  In addition, one of our customers has specified a 2
minute, 80 volt survival test.

The obvious solution of a LM2931-5.0 with a 32V over-voltage shut-down will
not work.  Way too much heat for a little linear regulator.

I have a working option which will allow 10 to 80+ volts in, 5 volts out
with about .25 volts of ripple.  This is really just a voltage comparator
maintaining a voltage on a capacitor with a Schottky diode in the hysteresis
loop.  This is built with discrete transistors to allow the large supply
voltage range.

I know very close to nothing about switching power supplies, but I suspect
that there is a buck regulator which will do this in a neat package.  I have
looked in the obvious places, but I cannot find a device which will take the
high input voltages in a small (low pin count) package.  I prefer to not
have an inductor in this supply, current demand is low, I wish to minimize
stray magnetic fields due to the Hall effect sensor, and there is so little
space.

If any of you PICsters have any suggestions or cautions about how to achieve
the above, I'd love to hear about them.

Thanks!


____________________________________________

Lyle Killough      lyle@suregripcontrols.com
____________________________________________

           Sure Grip Controls Inc.
             4 - 1413 McGill Road
            Kamloops, BC, V2C 6K7
                   Canada

              phone 250-374-2278
              fax   250-374-1099

____________________________________________

          www.suregripcontrols.com
____________________________________________

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