S-100 power supply voltage ranges

[Allison]

Some S100 chassis had multiple primary taps, CVT or a in the case of 
Inetgrand {and a few others} boxes regulators. 

The problem is the early machines had to have really robust transformers
as the +8V bus could easily be 25A using early boards.  By 1980s with 
64k ram cards (64k on one card) and multi serial IOs on one board a 
typical system might take from 3-5 board at far lower current than the 
earlier 4k ot 8k based memory systems.  The side effect fo that was the 
bus voltages being upregulated would float higher and regulators would
run really hot.  Near the latter days typcail systems were system on a 
card (z80, 64k or even 128k, 2 serial, FDC and printer port) making the 
whole load typically under 3-4A at +8V and the need for more boards 
unlikely.




Allison


>
>Subject: Re: S-100 power supply voltage ranges
>   From: "Barry Watzman" <Watzman at neo.rr.com>
>   Date: Mon, 02 Mar 2009 10:42:55 -0500
>     To: <cctech at classiccmp.org>
>
>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
>effective.
>
>
>------------------------------
>
>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>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
>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.
>
>