10 Apr
2008
10 Apr
'08
3:16 p.m.
On Thursday 10 April 2008 17:28, Tony Duell wrote:
The prolem is that if this is like most small SMPSUs, then almost all the
'interesting' circuitry (oscillator, etc) is on the mains side of the
isolation barrier. And therefore you can't just connect a 'scope to it,
not unless you like shorting out the mains via one of the rectifier
diodes and the earth (ground) lead of the 'scope.
This is true, though at the time I wrote that I was thinking about scoping
the outputs.
I think it's reasonable to asusme the chopper is
working (otherwise
you=
'd
get no outputs at all). Does it seem to be
running continuously, or do
you get the 'tweet tweet tweet' of a PSU that's starting, detecting a
fault, shutting down, and repearing?
Scoping tbings in there would sure be informative. The right way to do it, of course, is to use an
isolating transformer,
but not everybody has one of those in the workshop. I certainly do not
recomend 'floating the scope;' (removing its earth lead so the 'scope
chassis can sit at half mains voltage, or whatever), even though this is
suggested in one service manual I have if an isolating transformer is not
avaialble. I have this objection to large metal ohjects sitting at
dangerous voltages.
Yes indeed.
One way to achieve isolation is to get a couple of filament transformers that
are of similar voltage ratings and use them both, tying both low-voltage
windings together and using one primary as the output. I'd think that they
wouldn't need to be particularly hefty if you're not going to load the supply
much.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin