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Old 1st August 2006, 12:26 PM   #1
AndrewT is offline AndrewT  Scotland
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Question Rectifier snubbing caps ?

Hi,
various caps are available:- Metalised Propylene, Metalised Ester, Foil Styrene, Silvered Mica, NP0 Ceramic, High dielectric Ceramic and the cheaper Metalised Plastic films.

I have deliberately excluded the exotic foils and Teflon due to cost.

Which type best suits an RC snubber across the rectifier diode?
and which should be avoided? Assume a range of 10nF to 100nF

Which type best suits high frequency spike absoption across the low voltage AC input to the rectifier and again which should be avoided? similar range to above

Finally, which type best suits capacitor only bypassing the rectifier output before it leaves to feed the smoothing caps? 100nF to 1uF or is an RC snubber a "must have" in this location?

An order of preference would be nice to know.
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Old 1st August 2006, 03:07 PM   #2
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without a resistor to change the transient into heat "dair ain't no snubbin' action going on down dair" Andy.

the value of the cap has to be determined empirically -- values I see are a couple nF.

sincerely, Amos

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Old 1st August 2006, 04:17 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi Jack,
I am leaving room for a resistor AND capacitor to form an RC snubber across each diode of the bridge.

I am asking about what TYPE/dielectric of capacitor suits the function.

Thanks for the info that 10nF as my lower range limit is a bit too high.
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Old 1st August 2006, 05:13 PM   #4
MRupp is offline MRupp  Germany
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Quote:
to form an RC snubber across each diode of the bridge.
Wouldn't a single RC snubber accross the transformer secondary be enough, plus a parallel cap to lower the ringing frequency, as described in Jim Hagerman's article?

To my knowledge, "lossy" caps would be suitable, as long as they have a high resonant frequency, that is, well above the expected ringing frequency? For example, Rifa MP caps may be a good choice I have some (old) 100 nF Rifas with a f zero of 3.6 or 4,9 MHz (2 types).
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