New pcb design for S-100 prototype board available - test-drb@ccmp.vtda.org

3 Jun 2007

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Subject: Re: New pcb design for S-100 prototype board available
   From: woodelf <bfranchuk at jetnet.ab.ca...

   Date: Sun, 03 Jun 2007 11:39:32 -0600
     To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org...

Al Kossow wrote:
> 
> If you are doing a design with on-board regulators in the 21st
> century, why not use integrated switching rather than linear
> regulators?
> 
> Heat dissipation will be MUCH lower if you do this. 
the real problem was NOT the heat from the regulators but the 
heat from the rest of the board.  8K of 2102 memory produces 
a lot of heat and a box with 8 of them needed a good set of fans
to move that heat.

FYI: even the 2102LP parts were around 50mA each (512 *.05=25.6W)
and the more common parts were around 80-100mA. Add regulators and
that could easily total 40-60W of heat.  Add a few IO, Floppy card
and CPU and now your cooking.  If the drives are in the box add 
fans accoringly.

Dont forget the average 8V bus PSU was (in a decent box) rated to 
deliver that voltage at 25A (125W of 5V alone).  Some boxes like 
the Compupro and Intergrand had CVCC transformers that typically ran
hot as well.  So the average S100 grate needed to move between 100
for a small system to as much as 500W of heat.  

...
 True, but with the advent modern chips like CMOS I see
that
power consumption less of a problem. Is the proto-board
for 8 bit S-100 or 16 bit S-100 as I remember some where the buss
was upgraded for 16 bit processors? ( Can you say INTEL ? )
If it where not for that fact, having De-codeing and buffer chips
laid out as that would save some space rather than in the pro-type
area. 
CMOS will help, denser memories (even back then) really help.

Allison

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