Robert A. LaBudde wrote:
>

> => Snubber network consists of a series 22 ohm, 0.25 W resistor with a 0.1
> uF 250 V capacitor. This will near-optimally damp EMI and and limit
> back-emf to 176 volts.
>
> Any comments as to the adequacy of this analysis or set of design rules?


>From years of inspecting commercial equipment I
feel you have underated the parts. From gueswork
I would go to a 1w or 2w resistor, mounted 1cm
above the board to keep heat away from the board,
and for the capacitor you will often find a 630v
poly cap is a similar size and cost to the 250v
poly cap. Many suppliers only stock the 630v caps.
Sourcing them may be easier, even cheaper.
And they are a much better part if it will be
exposed to mains spikes and lightning etc.

Your values sound good, I am always seeing 22ohm,
27ohm snubbers with 0.1 and 0.15 uF caps in TV
and VCR mains switching supplies. Most manufacturers
are using the 2w round resistors, these are a
high temp device with the matt red/green paint,
usually mounted above the board and on better
units mounted on ceramic lifters.

If in doubt, build it and measure the temp-rise of
the parts when run testing. I always tune snubbers
this way. :o)
-Roman

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