From: "Christopher R. Carlen"
Subject: Re: Core gapping techniques and general SMPS magnetics stuff
Date: Tue, 17 Dec 2002 10:51:31 -0800
Organization: Sandia National Laboratories, Albuquerque, NM USA
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Tony Williams wrote:
> My quick doodles (in oersteds and gauss, so probably wrong) suggest
> that, with a 0.35mm gap, ue drops to about 107.
That's reasonably close to the value in the catalog of 140.
> But that is theory, disregarding the effect of fringing, which will
> be large with such a small gap.
I would have thought that fringing would increase with increasing gap
length. I would enjoy understanding this better however, if you want to
explain how it works.
>> With the new number of turns I get H=948 A/m.
> H = 4.pi.n.I/10.le for an ungapped core.
> H = 4.pi.n.I/10(le + u.d) for a core with gap= d.
> (le and d are in cm in this old system.)
> Which I think brings your H down to about 71 A/m.
> Which is more consistent with the fact that the resultant flux
> density, B, has come down from 540mT to 167mT.
My patience has simply run out for inconsistent H and B formulas. (Not
your fault, it's just that I don't trust any formula I haven't derived
myself.) So I am going to start a thread about this. Please see
"Deriving H for magnetic cores"
Thanks for the input,
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA