S-100 power supply voltage ranges

Barry Watzman Watzman at neo.rr.com
Mon Mar 2 09:42:55 CST 2009

Actually, the factory fix was a "bucking transformer", a whole second power
transformer installed out of phase in series with the primary power
transformer so that the voltages were subtractive.  There is a factory ECN
on this topic.  But the bridge regulator solution was common among the user
base (I myself have used it) as a lot simpler and cheaper, and almost as


Message: 3
Date: Sat, 28 Feb 2009 11:07:56 -0600
From: Jim Battle <frustum at pacbell.net>
Subject: Re: S-100 power supply voltage ranges
To: General Discussion: On-Topic and Off-Topic Posts
	<cctalk at classiccmp.org>
Message-ID: <49A96F6C.6060602 at pacbell.net>
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Chuck Guzis wrote:
> All of the S100 boards I've seen use simple linear regulators, so you
> need some headroom--but not too much.  A lot of S100 7805s and LM323- 
> 5s were operated within an inch of their maximum current ratings (some 
> had bypass resistors installed) and generated a lot of heat.  I
> wouldn't run the supply rails any higher than I had to.
> Cheers,
> Chuck

The Sol-20 had an app note about this problem.  Apparently they shipped them
for a while with transformers that were out of spec with the end result that
the unregulated power ran high.  The recommended fix was to take a power
bridge, mount it to the case, and wire it in series with the positive
voltage run in order to get a ~1.4V drop.

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