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John,

I wonder if we are trying too hard on the +12V issue. Couldn't you
simply let it float free with something like a MOV to keep it from
getting too high? If the voltage goes too low, a simple current limiting
sacrificial resistor (AKA fuse) would protect the equipment. You could
even use one of those self healing plastic fuses.

Looking at the design again, there won't be any hard drives or fans to
suck juice from this voltage, so the only thing it will be powering is
the PCI bus.

John wrote:



Yes I did a little research on it and the only thing the negative is needed
for is the rs232 serial ports. for this you can get a $1.50 ic to convert
+12 to -12 V low current.
That said, what I'd do is get a 1.5 amp 5v TO-3 regulator and a 1 amp TO-220
regulator along with one of the TO-220 adjustable 1 amp regulators for the
3.3 v and run it all off the 12V (highly filtered) input. That said,
(again) you might have problems with th 12V regulator if the input drops
below 13.8V! So you might need to use a separate battery for it and diode
isolate it from the aircrafts electrical systm and have it charged when it
exceeds the 13.8 volt figure.
John


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