From: Douglas C. Smith ([email protected])
Date: Wed Mar 14 2001 - 08:33:12 PST
Hi All,
I have been asked the following question by one of the list members:
Doug, could you recommend a general strategy to avoid EFT problems? LC
circuits?
Any time two pieces of metal at different potential contact each other,
a spark occurs, either EFT (a series of sparks at something like a MHz
rate) from power currents or ESD from static potentials. The problem is
that the EFT occurs inside a system when a board is plugged in while the
system is powered up (referred to as hot plug-in). While pin connect
sequencing with RC/LC networks can help the problem remains to some
extent.
Although not an EFT or ESD effect, I have even seen a path carrying
in-rush current crosstalk enough into nearby paths on a board to burn
out devices!
To be safe, if a system has a power bus (higher voltages are worst) one
should apply IEC 61000-4-4 EFT bursts to the bus though HV coupling
capacitors. For 48V buses, I have had good luck with correlating a 1000V
level to proper system functioning in a hot plug-in environment. Several
of the measurement techniques on my website, such as using a "paperclip
probe" or a pair of good matched current probes and phase information,
can be used to trace noise currents through the system and measure its
effects.
I have some general information on EFT on my website under the
"Technical Information and Downloads" and "Recent Talks and
Presentations" headings at http://www.dsmith.org . The EFT talk visuals
will prompt for a password. It is: need2see
Hope this helps.
I was just in the Boston area last week and saw more than enough snow to
last me several years! If you would like to have an excuse to get some
California sun, I talk about some of these kinds of issues in my seminar
in Los Gatos next month.
Doug
--
-------------------------------------------------------
___ _ Doug Smith
\ / ) P.O. Box 1457
========= Los Gatos, CA 95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
/ /\ \ ] / /\ \ Mobile: 408-858-4528
| q-----( ) | o | Email: [email protected]
\ _ / ] \ _ / Website: http://www.dsmith.org
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