> > Yes, that sounds 100% reasonable. I may be from Cambridge, but I do
> > understand _some_ electrical engineering :-) (Seriously, I had to explain
> > jsut that to a 3rd year student in electrical engineering the other
> > week..... There is something wrong with the world.)
> You got my ears peaked up. What was that trouble with this 3rd
> student's error?
A couple of things. Firstly I had to explain that if you connect
cells/batteries in series then the voltages add but if you connect (equal
voltage) them in parallel the voltage is unchanged but the internal
resistance and capacity are increased. Secondly I had to explain that as
the battery could 'float' with respect to the 0V rail, you could use a -5V
regulator as a supply for a board of logic devices.
> >
> > After all 'There is no such thing as ground' What you take as a 0V
> > reference is entirely up to you.
> Really? Common, ground, 0V, neutral, power return makes my mind spin
> but I adapt to what you're talking about...so you're not talking
> mumbo-jumbo stuff. :)
The point is that you can connect the -ve lead of your voltmeter wherever
you like. There is no god-given 0V point. If you have a circuit that takes
in 3V and gives out -5V (a common SMPS chip can be configured to do just
that) you can easily run some TTL from it. The '-5V' line from the PSU
becomes the '0V' line on the logic and the '0V' line on the PSU is the
'+5V' line on the logic.
Of course you have to be _very_ careful if any voltages are referenced to
anything else, like mains ground.
> I know about this linears heating problem and I do have a old Asus
I have a 5V 50A _linear_ in one of my Unibus expanison boxes (a 3rd party
one - DEC almost always used SMPS's). It runs hot.
> Jason D.
--
-tony
ard12_at_eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill
Received on Mon Jun 23 1997 - 21:57:28 BST