Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!sdd.hp.com!hplabs!hpfcso!hpfcdc!kingdom
From: kingdom@hpfcdc.HP.COM (Mike Kingdom)
Newsgroups: sci.electronics
Subject: Re: NEGATIVE VOLTAGE?
Message-ID: <4660009@hpfcdc.HP.COM>
Date: 15 Mar 91 00:44:22 GMT
References: <1991Mar8.140031.20095@uncecs.edu>
Organization: HP Fort Collins, Co.
Lines: 16

> In article <1991Mar8.182508.15573@zoo.toronto.edu> henry@zoo.toronto.edu
> (Henry Spencer) writes:
> >I'm not sure why -12 is such a problem.  The circuits for negative supplies
> >are no more complex than those for positive supplies, and IC regulators are
> >just as available.
> 
> Unfortunately, this last statement is not true.  For some reason, positive
> regulators are more common.  You can probably find what you want in a negative
> regulator, but you won't have as much of a choice.

The normal thing to do for disk drive supplies and the like which use +/- 12V
is to build the +12V section like usual with a 7812 regulator and build an
analagous circuit using a 7912 regulator for the -12V section. This is a
non-switching type of supply.

-- Mike