Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: question about computer power supply
Summary: Beware of unconnected power supply "sense" line
Keywords: computer power supply
Message-ID: <3852@kitty.UUCP>
Date: 15 Jul 90 23:27:47 GMT
References: Experience <30733@eerie.acsu.Buffalo.EDU>
Distribution: sci
Organization: Recognition Research Corp., Clarence, NY
Lines: 29

> >I recently bought NCR PC-6 power supply to power some hobby projects.  When I
> >received the supply, I measured the outputs. The +12V line measured +4.95V
> >and +5V line measured +4.8V.  I have been told that the +12V line will not
> >be +12V until a load is connected to the supply.  I was told that the scheme
> >was somewhat like the IBM 'goodline', whatever that is.
> 
> 	I don't know about that NCR PC-6 supply,but I do know that the IBM 
>  power supply gives the expected voltage without a load being apply,if my 
>  memory serves me right.So in that case,I would assume that maybe something 
>  is wrong with that NCR job you have.  

	I have no specific knowledge of the NCR PC-6 power supply, but I
would like to point out something that I have seen on other computer power
supplies which *could* be your problem.

	Some well-designed power supplies provide an external sense lead
which is connected to a terminal on the PC-board backplane.  This will
automatically compensate for any IR drop between the supply and the
backplane.  If your power supply has a multi-pin connector whose pin
functions are not explicitly labeled or otherwise known, it may be that
one or more pins are for sense purposes.

	Failing to connect a voltage sense lead to the power output lead
will result in an incorrect voltage with lack of regulation (usually, but
not always a *lower* voltage).

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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