Path: utzoo!news-server.csri.toronto.edu!rutgers!sun-barr!cs.utexas.edu!uunet!mcsun!ukc!warwick!esupg
From: esupg@warwick.ac.uk (Andrew Bargery)
Newsgroups: sci.electronics
Subject: Re: NEGATIVE VOLTAGE?
Message-ID: <2RH&P6_@warwick.ac.uk>
Date: 13 Mar 91 13:34:28 GMT
References: <1991Mar8.140031.20095@uncecs.edu> <1991Mar12.174440.26009@tc.fluke.COM>
Sender: news@warwick.ac.uk (Network news)
Organization: Computing Services, Warwick University, UK
Lines: 26
Nntp-Posting-Host: clover

>In article <1991Mar8.140031.20095@uncecs.edu> crisp@uncecs.edu (Russ Crisp) writes:
>}
>}I'm in the midst of a construction project that, when complete, will
>}require a -12 volt power supply, a +5 volt, and a +12 volt supply.
>}I can handle the +5, and the +12, but the -12 is vexing me.  Can
>}I use another independent 12 volt supply, and reverse the leads,

YES!!

if you have got another 12v power supply handy then this is no problem. The
normal method is to reference 0v to ground. If you connect the +ve terminal to
ground, then the negative terminal will be at -12v wrt gnd (0v). You don't
even have to connect the 0v to ground; all the voltages in the circuit are
relative to each other, so you could use -12,0,5,12 or 0,12,17,24 or
988,1000,1005,1012 volts - the circuit will still work. However, if you are
going to connect scope probes, etc, then 0v on the board must be at the
same potential as in the scope, IE. GND

I have used this method to produce -5.2,-2,0 , -3.2,0,2 and (currently)
-16,-5,0,5,16 volt power rails. However, I don't think you can use this method
if you are using switch-mode power supplies.

------------------------------ esupg@uk.ac.warwick.cu -----------------------
  DISCLAIMER:       Andrew     University of Warwick, Coventry, UK.
                     Bargery   154 Brunswick St, Leamington, CV31 2ER, UK.
I plead the 5th...             vox : +44 926 881264