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Reply-To: "Fred Bartoli"
From: "Fred Bartoli"
References: <6hNK9.982$qA3.firstname.lastname@example.org> <3DFC2439.5F2A4EC7@ieee.org>
Subject: Re: Core gapping techniques and general SMPS magnetics stuff
Date: Sun, 15 Dec 2002 12:14:56 +0100
X-Newsreader: Microsoft Outlook Express 5.00.2919.5600
Organization: Guest of ProXad - France
NNTP-Posting-Date: 15 Dec 2002 13:19:05 MET
"analog" a écrit dans le message news:
> Mike Engelhardt, Chris Carlen wrote:
> >> So I will have to gap my cores. How do you folks gap E-cores for
> >> prototype/low volume applications?
> > Shims work and even, unforturnately, get into production sometimes.
> > I had a Lambda SMPS with shims in the outer legs. But the fringe
> > fields interfered with the the scanning electron microscope it was
> > powering so I swapping out that power supply with one that had used
> > properly gapped magnetics, i.e., a gap only in the center.
> A distributed gap (which is better approximated by gapping all three
> legs) will fringe less into the windings and will generally lead to
> better performance in flyback applications. Usually a shorted turn
> around the outside of the core in the form of a band of copper tape
> will suffice to contain external leakage fields it that is a problem.
> However, if you do this, be sure to space the band at least two or
> three gap lengths away from the core in the vicinity of the gap in
> order to avoid inducing excessive eddy currents in the copper band.
how far is excessive ?
I've just release a 200W isolated SEPIC PFC.
I don't have the figures at hand but IIRC the gap was 1mm inner and outer
legs with the shorted turn directly wound on the core.
Efficiency was 90/91% and I didn't notice any heating of the shorted turn.
Maybe I'll check this if I have some time.
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