5 Feb
2012
5 Feb
'12
7:11 p.m.
Absolutely. A colleague once told me about equipment
he worked on in
telephone exchanges. He wondered what the -43V supply was for, until he
realised it was the power rail for the TTL. The -48V was the "ground"
for it.
Seems entirely reasoanble :-).
I beelive one of Vonada's laws is 'There is no such thing as ground'.
That statement has 2 meanings :
1) Voltmeters have 2 leads, it is potential differences that matter. A
circuit that needs 12V can run between a +6V and -6V rail (referenced to
something you happen to call ground)
2) All connections have some impedance (particularly inductance) so 2
connections you think you've connected to the point you choose to call
ground might well have a significant voltage between them.
It's the first meaning that applies here, of course.
To get mildly on-topic, I believe there's a TTL IC on one of the boards
in an RK05 that is powered between a +10V line (generated o nthat board)
and the main +15V line.
-tony