Derek,
We stock a 16 amp line filter which we have used on lower current products
specifically to prevent saturation of the choke when used as a protective
device for external events such as EFT. I put one on a product containing an
"industrial" computer supplied by a business partner to solve a problem with
Ethernet communications during EFT testing. Interestingly, although the
computer was CE marked, EN61000-4-4 was absent from the list on the
compliance label. I had a tough time convincing the engineering manager that
the larger device was needed. He wanted to use a smaller filter that replace
the IEC cord inlet.
The answer to your question is that, in the absence of reliable data from
the vendors, you must either devise a quick test or deal directly with a
good custom magnetics house that will build a part to your specs.
Unfortunately, today we often find ourselves dealing with "puppies" after
the "old dog" engineers have either retired or been laid off. A lot of these
kids don't know, don't care, and think truthfulness is an impediment to
sales. It can be difficult tell stupidity from malice as they both cause
similar problems.
Scott Lacey
-----Original Message-----
From: Derek Walton [SMTP:[email protected]]
Sent: Thursday, December 02, 1999 2:47 PM
To: IEEE EMC Discussion Group
Subject: Common Mode Choke
Good day all,
I'm refining the input filter of a 150 watt SMPS. Nothing flashy,
just a
few caps and a common mode choke.
The current is drawn by the supply in short bursts as the DC link
cap is
charged. I've shown that peak current reaches 6 amps for up to 2 ms.
I've also demonstrated that the CM choke, while rated for the RMS
current ( a 2 amp device ), does saturate when the current exceeds
about
4 amps.
I've been trying to find out from the vendors, what current it takes
to
saturate the CM choke. I've had answers from CM chokes can't
saturate to
"that's not an important parameter, use the rms figure"....
My question is, with over 20 potential vendors of this type of
component, is there any way I can find out saturation performance
without buying one of each type and testing it. I've played with 3
so
far, the most expensive was NOT the best! I guess, I'm curious why
more
folks don't know about this effect also.....
Thanks,
Derek Walton
Owner
L. F. Research EMC Design and Test Facility
12790 Route 76,
Poplar Grove,
IL 61065.
www.lfresearch.com
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