On Mon, 21 Jan 2019 16:23:49 -0500, Clare Snyder
wrote:

On Mon, 21 Jan 2019 14:36:31 -0500, Tekkie®
wrote:


In electronics and automotive electronics 5 volts seems to be the standard.
I am curious as to how this was made the standard.

The 5 volt standard goes WAY back to TTL logic
As for the origins of 5V/TTL, that was a set of design tradeoffs. If
you find a schematic of a TTL gate, you'll notice that it needs at
least 3 diode drops internally, plus various resistor drops. What that
doesn't tell you is the choice of reference currents (1.6 mA for a low
input) which was in part determined by the current levels required to
produce acceptable switching speeds. These current levels in turn set
limits on the internal resistor values, and the voltages needed to
feed them. You also need to factor in the state of semiconductor fab
capability - the first TTL circuits were at the edge of what could be
reliably produced. Imagine - 20 to 100 gates on a chip! That's (gulp)
hundreds of transistors, with the masks all laid out by hand. All of
this, including power dissipation limits, resulted in the standard TTL
supply voltage spec of 4.75 to 5.25 volts. As it turned out, this was
an adequately wide margin for practical systems, and the speed (10 -
20 MHz) was adequate for a wide range of applications. So TTL became
king. Even then, if you wanted faster speed there were other families
available, like 74S and ECL, but those puppies were even bigger power
hogs than TTL. Go look up the construction techniques for the first
Cray computers


IBM's high speed logic used +0.9 and +1.9 levels for a "0" and a "1"
in the S/370 days when LSI "transistor logic" ICs were the thing.
The power rails were 1.5v and 3v. Keeping the voltage down made
switching faster and reduced power consumption but they were still
power hogs compared to the CMOS that followed.
You could easily have a 1.5v power supply running close to 100 amps.
The big systems were water cooled.