RE: How to power a PCI card from either 3.3V OR 5V..

[Dimiter Popoff <tgi@bulnet.bg>]

Since the poor fellow who asked the question actually got no
answer, I attach a small circuit which I hope should help. It is
not for direct use, but is a good enough hint how to make it
with minimum components and sufficiently reliable. It is
shown for small currents (up to 0.5A) only because it
was easier for me to calculate and denote the whole thing in
a few minutes, one can expand it easily. One could also use
PMOSFETs as power switches, though their drive at 3.3V may
become an issue - and price could also be a factor.
 
BTW, wether 7.5W or 25W max, power source switching (assuming zero
loss at the switch) will result in 33% power saving - not
negligible at all.
 
The attached file is a hpgl drawing, you can either import it
in Coreldraw or plot it on a 7475... (if you know what this was :-) ).
 
Hope I have helped,
Dimiter
 
Dimiter Popoff
Transgalactic Instruments, Gourko Str. 25 b, 1000 Sofia, Bulgaria
http://www.freeyellow.com/members2/transgalactic/
Email: tgi@bulnet.bg, tgi_earth@yahoo.com
Phone: 00359/2992/3340, 00359/2/9805997, Fax: 00359/2/9540384

pwsw.hpgl