Re: Self-resonance of X capacitor.

Posted by Jacques (A) on August 30, 2005 at 01:11:21

In Reply to: Self-resonance of X capacitor. posted by Al Sekela on August 29, 2005 at 11:56:19:

That low? I should have thought a self-resonance in the 40-50MHz.
That said, I checked attenuation curvers of standard filters from Schaffner
and Timonta and, if attenuation curves show a plateau from 15-20Mhz
depending on the model, attenuation stays above 40dB up to 50MHz, which is
what counts ;-)
As for chokes, RFI attenuation chokes use a mix of core materials that show a
high dissipation factor above the self resonance frequency (which is rather
low as you expected it, say in the low MHz). These high core loss lower the
Q of the self resonance. A typical attenuation (when fed by a 50Â½ source
towards a 50Â½ load) is 50dB at 1MHz going down to 20dB at 50MHz.

Furthermore, there is a very neat trick to get rid of most the ESL (serial
inductance) of an attenuation cap. By using a "transformer" made of a few
spirals on both sides of the pcb, (without core!), and by connecting the
"primary" in serial with the incoming signal, and the "secondary" in serial
with the X cap, you can get cancellation of the ESL since this xformer,
thÅ½venin-transformed, behaves in its cap branch as a ... negative
inductance. I read a very interesting paper on this in IEEE Power
Electronics Society Proceedings. Amazing how layout can be in,strumental in
building a good filter. If you want, i can check if I can get it in
electronics form. Obviously, I can't put it on a public forum without
infringing IEEE rights, which I won't... Send me an email.
I cannot go further right now, lack of time. Cheers

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Follow Ups Full Thread

Topic - Steve E. or anyone -Grounding...Again - dado4 06:23:00 08/26/05 (17)

Re: Steve E. or anyone -Grounding...Again - Dan Banquer 11:09:00 08/26/05 (16)

Re: Steve E. or anyone -Grounding...Again - Jacques 03:00:16 08/27/05 (15)

Re: Steve E. or anyone -Grounding...Again - Dan Banquer 08:43:17 08/27/05 (14)

Re: Steve E. or anyone -Grounding...Again - Jacques 06:08:09 08/28/05 (13)

Re: Steve E. or anyone -Grounding...Again - Jacques 06:20:23 08/28/05 (12)

Noisey Earthground???? - Dan Banquer 12:50:08 08/28/05 (11)

Re: Noisey Earthground???? - Jacques 04:26:27 08/29/05 (10)

Re: Noisey Earthground???? - jea48 18:50:30 08/30/05 (1)

Re: Noisey Earthground???? - Jacques 07:24:15 09/01/05 (0)

Self-resonance of X capacitor. - Al Sekela 11:56:19 08/29/05 (6)

Re: Self-resonance of X capacitor. - Jacques 01:11:21 08/30/05 (5)

Re: Self-resonance of X capacitor. - john curl 15:00:03 08/31/05 (3)

Re: Self-resonance of X capacitor. - Jacques 07:29:01 09/01/05 (2)

Re: Self-resonance of X capacitor. - john curl 07:55:28 09/01/05 (1)

Re: Self-resonance of X capacitor. - Jacques 08:14:42 09/01/05 (0)

Thanks for the comments. - Al Sekela 14:15:55 08/30/05 (0)

Re: Noisey Earthground???? - Dan Banquer 09:20:45 08/29/05 (0)

Follow Ups

Re: Self-resonance of X capacitor. - Jacques 01:11:21 08/30/05 (5)

Re: Self-resonance of X capacitor. - john curl 15:00:03 08/31/05 (3)

Re: Self-resonance of X capacitor. - Jacques 07:29:01 09/01/05 (2)

Re: Self-resonance of X capacitor. - john curl 07:55:28 09/01/05 (1)

Re: Self-resonance of X capacitor. - Jacques 08:14:42 09/01/05 (0)

Thanks for the comments. - Al Sekela 14:15:55 08/30/05 (0)

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