1 Feb
2009
1 Feb
'09
1:10 p.m.
The part of this that really amazes me is where it says something like "long
power supply input lines" can also cause problems or oscillation. I suppose
Well, it's farily common for long (or otherwise high-inductance) power
lines to cuase problems in some circumstances. That's why we use
decoupling capacitors on logic boards :-)
This could be a problem with a DC-DC converter or similar (in other
words, if you're using one of those, make sure you decouple the input
side well).
But it shouldn't be a problem with mains-input SMPSUs, at least not
normal ones./ In the normal small SMPSUs, the chopper drive is not
synchronised ot the mains frequency [1], so there's no way of the supply
knowing waht the mains input will actually be when the chopper turns on.
And thus the enrgy from the mains is stored in large (and low impedance)
capactiros, the chopper effecrtively runs off that. So the HF component
of the mains input current whould be prtty small, and thus the adition of
mains filters or input wiring shouldn't be a problem
[1[ There heve been supplies using SCRs triggered at the right point in
the mains cycle. They're not common, they put a lot of 'hash' back on the
mains and are geenrally frowned upon.
-tony