Low frequency conducted noise is usually generated by the periodic demand on
the energy storage cap (greatly, greatly affected by esr). This noise is
"differential" and no y-cap (unless it's so large it becomes a killer size,
and then not really) will stomp on it.
Your first problem (conducted emissions) is trying to get rid of the
fundamental of the power supply which can be a bit challenging.
You see, the y-caps are low impedance *AND* your noise source is low
impedance, so adding y-caps is not going to "short" out that noise source.
The best way to solve your problem is is to use minimum esr caps and, of
course, very judicious layout inside the supply.
There are external things you can do, but they can get bulky.
How much power does this supply take? Do you have control over the
manufacturing process at all?
Once you've tackled the conducted emissions, we can move on to the radiated
emissions.
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
619 North First St, San Jose, CA 95112
-----Original Message-----
From: Lou Guerin <[email protected]>
To: [email protected] <[email protected]>
List-Post: [email protected]
Date: Friday, December 21, 2001 10:49 AM
Subject: power supply to GOST 30429-96
>
>Dear Fellow EMC workers,
>I am trying to get a SMPS to pass this GOST standard and am having a devil
>of a time getting it done. After 3 days of mitigation testing at our local
>lab we are still out at the low frequency range 10-60kHz and at 15-50MHz.
>We pass the Class A limits for CISPR 22 but these GOST limits are far more
>stringent. The power supply is convection cooled in a IP66 box that is
>powering a repeater. We have been able to determine that the noise is being
>generated by the power supply and thus far we are not able to suppress all
>the low frequency and high frequency conducted noise. I have copied the
>limit requirements below for your review.
>Has anyone run into this standard before? Is there something we may be
>overlooking? We are not using a custom supply, this is an off the shelf
>supply that we are packaging into a IP66 box. The usual "fixes" didn't seem
>to work, X and/or Y caps, ferrite beads, inductor. These were applied
>liberally during the past 3 days.
>The requirements for EMC of radio equipment in Russia (as well as in
several
>other CIS countries) are set by the standard GOST 30429-96 (Electromagnetic
>Compatibility of technical equipment. Man-made noise from equipment and
>apparatus used t6ogether with service receiver systems of civil
application.
>Limits and test methods), according to this standard the following
>measurement must be done.
>1. Conducted Emissions
>Frequency range Limits, dB(uV)
>0.009 MHz - 0.15 MHz U = 90 - 28.9lg(f/0,01) (Quasi-peak)
>0.15 MHz - 0.5 MHz U = 66 - 22.7lg(f/0,15) (Quasi-peak)
>0.5 MHz - 6 MHz U = 54 - 12.97lg(f/0,5) (Quasi-peak)
>6 MHz - 30 MHz U = 40 (Quasi-peak)
>30 MHz - 100 MHz U = 48 (Quasi-peak) 40 (Average)
>
>This test is done looking at the emissions from the 220 V power cables,
>using a LISN
>2. Radiated Emissions
>Frequency range Limits, dB(uV/m)
>0.01 MHz - 0.15 MHz E = 60 - 20.4lg(f/0.01)
>0.15 MHz - 30 MHz E = 37 - 7.39lg(f/0.15)
>30 MHz - 100 MHz E = 36 - 21.0lg(f/0.30)
>100 MHz - 1000 MHz E = 25 + 20.0lg(f/100)
>
>According to GOST 30429-96 this test is done at 3 meters in frequency range
>0.01MHz - 30 MHz and at 1 meter in frequency range 30 MHz - 1000 MHz in the
>screen room.
>
>Any help will be eagerly accepted.
>Best regards and happy holidays,
>Lou Guerin
>Agency Approvals Manager
>Littlefeet, Inc.
>[email protected] <mailto:[email protected]>
>
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