Re: [uCsimm] HV capacitors on the LAN transformer

From: Tom Walsh (
Date: Wed Aug 15 2001 - 03:14:42 EDT

Slepov Dmitry wrote:
> Folks, who can answer this...

Try contacting the Pulse Engineering people. From discussions that I
had with them in choosing a magnetic to use with the SMSC LAN91C96
ethernet chip on one of my designs, I got the impression that this is a
"black art" of mysteries and enchantment.. When a designer is presented
with an unfamiliar technology, we rely upon people called "systems
engineers" of the product that we want to use, they refer us to other
"systems engineers" and eventually we get some 'magic numbers' to work

Bottom line? Electrical Engineering is such a wide discipline that you
have to rely upon other more specialized engineers.

I suspect that the 0.01 uf caps are there for the suppression of noise
(RF generated noise) and are needed to pass the U.S. FCC / Canadian
equivilant body emission standards.



> There is a LAN transformer on the ucsimm (VALOR- PULSE
> ENGINEERING part PT4153S). On most Ethernet designs,
> there are 2 1kV 0.01 capacitors connected to this
> transformer on the ethernet side. On the ucsimm these
> transformer pins are left unconnected. Question: what
> these capacitors normally for, why they are missing
> and is there any penalty for not having them?
> I will really appreciate somebody answering this
> question...
> Regards,
> Dmitry Slepov
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> This message resent by the list server

Tom Walsh - WN3L - Embedded Systems Consultant,
"Windows? No thanks, I have work to do..."
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