S-100 power supply voltage ranges

[Dave McGuire]

Barry Watzman wrote:
> 8 volts and 16 volts is correct.  Frankly, I would stay on LOW side (but not
> below 7.5 volts).  MANY systems burn up boards because they are towards the
> high side (it was a huge issue for early SOL-20's).  S-100 boards use linear
> regulators, and many of them pushed those WAY too hard, to the point that
> they got so hot they charred the board.  Some notable candidates includes
> the Tarbell double density controller card, the IMSAI SIO2-2 card and a
> number of memory cards.  At 9 volts, the linear regulator has to dissipate 4
> volts x {whatever current}.  A board like the Tarbell double density board
> has one regulator for the entire board, about 60 ICs including some big LSI
> chips (179x FDC & Intel 8257 DMA) and ONE linear regulator that gets
> ridiculously hot at even 8 volts.  The difference between 8 volts and 9
> volts is 25% and makes a HUGE difference.

   I'm not sure I'd consider that to be very good advice.  You make a 
good point about the power dissipation, but the dropout voltage of an 
LM7805 is about 2V...that's pushing the margin pretty tight.  If you 
ever have 500mV of ripple..

              -Dave

-- 
Dave McGuire
Port Charlotte, FL