EMI Suppressing Capacitors

Einric · 21st August 2011, 07:50 PM

Hello,

I have come across quite a few 10nF EMI suppressing Metalized Paper 1000VDC capacitors.
I am in need of a few 3n3 capacitors for a snubber circuit in my power supply.
Three of these 10nF caps in series will give me roughly 3n3.
What would be the benefits & drawbacks for using these in my snubber circuit?

Thanks.

DF96 · 21st August 2011, 08:42 PM

Would you need equalising resistors?

Einric · 21st August 2011, 09:06 PM

Yes, .1 Ohm, I've got that taken care of.

DF96 · 21st August 2011, 09:13 PM

I was thinking of something more like 100k-1M, to ensure that the applied voltage is shared evenly across the caps. Not necessary if your voltage can be handled by one cap.

jcx · 21st August 2011, 09:23 PM

snubbers are there for high frequency, series connection increases inductance making the series caps less effective

Einric · 21st August 2011, 09:41 PM

You wouldn't think that a few small caps would impede audio frequencies.

jcx · 21st August 2011, 09:48 PM

maybe you're talking about something else but in PS "snubber" has a very specific use - to cut RF/EMI generated by reverse recovery rectifier diode turn off spike

the problem is not audio frequencies, it the potential conduction/radiation of RF frequencies from the rectifier's fast current edge to sensitive semiconductor inputs where it can be "detected"/demodulated in the amplifying device nonlinearity

Einric · 21st August 2011, 09:56 PM

I See.

I'm working on the audiosector LM4780 Kit and there is an optional selection of a 3n3 w/ .1R in parallel to a 10,000uF for each rail. These components are referred to as snubber components. Would that be incorrect?

jcx · 10:58 PM

I don't know the Audiosector layout but to be effective the snubber networks should be right at the diode terminals with minimal loop area, short leads, extended foil construction if using film caps - try a search of diyAudio: username "Eva" and "snubber" will get you some real measurements

you should be able to use much smaller (physical size == less inductance) caps on the secondary = 100 V rating shoud be quite adequate for 22 VAC sec

Speedskater · 21st August 2011, 11:09 PM

Einric,
The capacitor pictured in your first post is a special type designed to safely take all the abuse of being placed across the AC power line.

21st August 2011, 10:54 PM	#9
jcx diyAudio Member Join Date: Feb 2003 Location: ..	I don't know the Audiosector layout but to be effective the snubber networks should be right at the diode terminals with minimal loop area, short leads, extended foil construction if using film caps - try a search of diyAudio: username "Eva" and "snubber" will get you some real measurements you should be able to use much smaller (physical size == less inductance) caps on the secondary = 100 V rating shoud be quite adequate for 22 VAC sec Last edited by jcx; 21st August 2011 at 10:58 PM.

21st August 2011, 11:09 PM	#10
Speedskater diyAudio Member Join Date: Sep 2002 Location: Lakewood, Ohio	Einric, The capacitor pictured in your first post is a special type designed to safely take all the abuse of being placed across the AC power line. __________________ Kevin

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21st August 2011, 08:42 PM	#2
DF96 diyAudio Member Join Date: May 2007	Would you need equalising resistors?

21st August 2011, 09:06 PM	#3
Einric diyAudio Member Join Date: Feb 2011 Location: Bozeman, MT	Yes, .1 Ohm, I've got that taken care of.

21st August 2011, 09:13 PM	#4
DF96 diyAudio Member Join Date: May 2007	I was thinking of something more like 100k-1M, to ensure that the applied voltage is shared evenly across the caps. Not necessary if your voltage can be handled by one cap.

21st August 2011, 09:23 PM	#5
jcx diyAudio Member Join Date: Feb 2003 Location: ..	snubbers are there for high frequency, series connection increases inductance making the series caps less effective

21st August 2011, 09:41 PM	#6
Einric diyAudio Member Join Date: Feb 2011 Location: Bozeman, MT	You wouldn't think that a few small caps would impede audio frequencies.

21st August 2011, 09:48 PM	#7
jcx diyAudio Member Join Date: Feb 2003 Location: ..	maybe you're talking about something else but in PS "snubber" has a very specific use - to cut RF/EMI generated by reverse recovery rectifier diode turn off spike the problem is not audio frequencies, it the potential conduction/radiation of RF frequencies from the rectifier's fast current edge to sensitive semiconductor inputs where it can be "detected"/demodulated in the amplifying device nonlinearity

21st August 2011, 09:56 PM	#8
Einric diyAudio Member Join Date: Feb 2011 Location: Bozeman, MT	I See. I'm working on the audiosector LM4780 Kit and there is an optional selection of a 3n3 w/ .1R in parallel to a 10,000uF for each rail. These components are referred to as snubber components. Would that be incorrect?

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