You do not need a metal case for an EMI filter. It is perfectly acceptable
to put a pair of Y capacitors, a common mode choke and an X cap on a
circuit board to form a basic line filter. (Be careful; if you use Y1
capacitors, a single capacitor may be used between line and earth. If you
use Y2 or Y4 capacitors, you must use two capacitors in series.)
The main reason for a metal case is to prevent radiated coupling of noise
from one side of the filter to the other. If you have a metal enclosure,
use a metal encased bulkhead filter. This is the best situation because it
will provide a high level of EMI suppression. If your product is in a
non-metallic enclosure, the filter case has less of an effect. Just make
sure that the filter is as close to the power entry as possible. If you
have a lot of unfiltered power lines around the electronics, noise can
radiate around the filter causing problems with conducted emissions.
Conversely, noise on the power lines can radiate around the filter and
cause problems with susceptibility. The filter will still help, but it
will not be as effective as a bulkhead filter with a metal enclosure.
Ted Eckert
Regulatory Compliance Engineer
American Power Conversion
The items contained in this e-mail reflect the personal opinions of the
writer and are only provided for the assistance of the reader. The writer
is not speaking in an official capacity for APC nor representing APC’s
official position on any matter.
Please respond to "POWELL, DOUG" <doug.pow...@aei.com>
To: emc-p...@majordomo.ieee.org, "Treg Listserv (E-mail)"
<t...@world.std.com>
cc: (bcc: Ted Eckert/SDD/NAM/APCC)
From: "POWELL, DOUG" <doug.pow...@aei.com> on 12/08/99 04:19 PM
Subject: RE: Open Frame EMI Filters
Hello once again,
I have already received a number of replies to my query indicating that the
metallic enclosure is required for low inductance coupling to the
components
or to prevent radiation between circuits within the product. This is not
my
question.
Please remember that one of the criteria that I described for the open
frame
is the passing all applicable EMC tests. This means that the open-frame
design that I propose meets both radiated and conducted emissions levels,
without the metallic box. My questions deals more with why is the
enclosure
required if product passes the tests without it. In the past I have
designed a few products with a simple PCB for emissions control. I
compensated for the internal re-radiation problem.
Recently I heard of a commercial EMI Filter company that says the enclosure
is required and that the encapsulant is a requirement. I disagree.
-doug
=======================================
Douglas E. Powell
Regulatory Compliance Engineer
Advanced Energy Industries, Inc.
1625 Sharp Point Dr.
Fort Collins, Colorado 80525 USA
m/s: 2018
---------------------------------------
970-407-6410 (phone)
970-407-5410 (e-fax)
800-446-9167 (toll-free)
mailto:doug.pow...@aei.com
http://www.advanced-energy.com
=======================================
> >
> > Hello group,
> >
> > For years I have used off-the-shelf and custom EMI filters
> with a fully
> > enclosed metal canister. Why is this enclosure required? Are there
> > specific provisions in the standards? My idea is to build
> up the filter
> > circuit on a printed circuit board and make it an integral
> part of the
> > power supply.
> >
> > I am currently looking at EN133200 which has certain seal
> tests but after
> > reviewing these, they all appear to be related to climatic or
> environmental
> > conditions. If the product passes these tests without the
> enclosure it
> > would seem that the product has passed, period.
> >
> > Alternatively I have considered removing the nomenclature
> "EMI filter" and
> > simply call it an input module, then evaluate it as a part
> of the overall
> > system. If it passes the EMC and Product Safety
> requirements, can I call
> > the job complete?
> >
> > Any thoughts?
> >
> > =======================================
> > Douglas E. Powell
> > Regulatory Compliance Engineer
> > Advanced Energy Industries, Inc.
> > 1625 Sharp Point Dr.
> > Fort Collins, Colorado 80525 USA
> > m/s: 2018
> > ---------------------------------------
> > 970-407-6410 (phone)
> > 970-407-5410 (e-fax)
> > 800-446-9167 (toll-free)
> > mailto:doug.pow...@aei.com <mailto:doug.pow...@aei.com>
> > http://www.advanced-energy.com <http://www.advanced-energy.com>
> > =======================================
> >
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