electro-Physics: 3.3 volts

From: 9000 VAX <vax9000_at_gmail.com>
Date: Thu Dec 9 23:04:28 2004

On Thu, 9 Dec 2004 21:30:20 -0500, John Allain <allain_at_panix.com> wrote:
> Today I started mothballing the VAX 6000 and noticed that a large part
> of its power supply is on 3.3 volts, now common, but probably not in 1988.
> Seems like something was invented, probably in chip design that made
> 3.3 so useful. I wonder what that was, when that landmark was reached.
> (For that matter, I don't really know why 5V and
> 12V were popular, on a "first priinciples" basis.)
> Maybe we've lost some of the people on the list who can answer these
> questions, but I'm trying anyway.
Well, I think I can answer those two questions about 5V and 12V,
though I am expecting 40~50 more years to live.

5V is popular because of TTL. TTL is made of bipolar technology on
silicon. Take a look of a simple NAND gate, and tune the voltages of
those transistors for speed, you end up with 5V power supply.

12V is popular because it is a multiple of 2V, which is the voltage of
lead battery. It is also a multiple of 1.5V, which is the voltage of
MnZn battery. Cars used lead bettery, and 12V was chosen (with 6
cells). I think this fact also increased its popularity.

I am pretty sure that the 5V answer is accurate. There might be better
reasons why 12V is popular.

vax, 9000
> John A
Received on Thu Dec 09 2004 - 23:04:28 GMT

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