-----Original Message-----
From:   Mark Willis [SMTP:mwillis@FOXINTERNET.NET]
Sent:   Saturday, October 30, 1999 9:35 PM
To:     PICLIST@MITVMA.MIT.EDU
Subject:        Re: power supply

I usually use DC 'wall warts' - Interesting!  I hadn't measured an AC
one, I just let someone else use those, usually.  I didn't anticipate
any real drop in voltage - guess I forgot about internal resistive
losses inside the transformer, which is already part of why a DC
plugpack "peaks" sans load.  Need a vacation here, obviously <G>

I used to use a DC Lump, put it through a reverse protection diode for
safety <G>, then a fuse & Zener for over-voltage protection (cheaper:
Use the reverse protection diode AS a fuse, not ideal but cheap!
<snip>

I used to repair car audio equipment, and most of the cheaper head units used a 1N400X wired accross the supplies for reverse polarity protection, relying on the in-line fuse to blow.  Of course, lots of people don't bother with the fuse, or wrap it in tin foil, or put a 6 inch nail in.  Under these conditions I have seen many of these little rectifiers fail to a short cicuit mode, the PCB traces then (usualy) take the place of the fuse.

Regards

Mike Rigby-Jones