[SunRescue] Ultra 1/170 motherboards.

[James Lockwood]

On Fri, 3 Sep 1999, Keith Campbell wrote:

> Do you (or anyone else here) know enough electrical design and know what is
> required to interface a PC powersupply with a U1 motherboard?  Care to draw
> up a circuit?  Something like this could come in very handy :-)

You could certainly do one with a couple TO-3 LM317's (you need a whopping
12A @ 3.0 and 3.3V) but there could be nasty issues due to the 2V voltage
drop (so you would need to feed them off of +6V minimum).  Feeding them
directly off of a +12V line through a 317 would be right out as you would
sink over 100W on each line.

My first-pass "simple" setup would probably be a voltage divider for the
+5V line using a pair of 2N3055's biased to output +3.0V normally, and use
the sense lines to bias the transistors back and forth.  As long as the
power consumption is relatively constant and the regulation of the
motherboard is quick this would work.  It's very brute-force, wastes
plenty of power (probably 10-15W per +3V circuit which there are two of)
but would be trivial to build.

Unfortanately, I don't have exact specs on the power supply feedback lines
and don't have a board around to test on.  I'd hesitate to draw up a
schematic without more information, but if any kind Sun engineer feels
like passing along specific information it wouldn't be difficult.

-James