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From: firstname.lastname@example.org (chris)
Subject: Re: SMPS transformer core power throughput calculation
Date: 15 Sep 2002 18:34:35 -0700
NNTP-Posting-Date: 16 Sep 2002 01:34:36 GMT
Robert Baer wrote in message news:<3D82411D.F686D4C8@earthlink.net>...
> Michael Denner wrote:
> > Hi
> > I'm difficulty calculating power output from the switching frequency & core
> > size. All the manufactures data I've come across present a graph of Po Vs
> > core volume for all their cores with a switching frequency of 20Khz. Great
> > if you want your psu to run at 20kHz!. Also there's generally three curves
> > one for each drive topology eg push pull flyback or blocking. In the same
> > breath they also state that the power output of the core increases with an
> > increase in frequency, which is what I want to calculate!. But no where can
> > I find a formula which will enable me to calculate what the output will be
> > for a given frequency , flux density, and a core area or volume.
Hi, there is no "formula" as such. The main consideration is temp rise
in the core. First you need to calculate the core loss which comprises
of 2 parts, hysterises loss and eddycurent loss. Both losses rise with
frequency and flux sweep. The other main problem is overload capacity,
that is you need to design for the worst case conditions, so "normal"
operation allways underutalises the core. If you need mains isolation
creepage distances as well then you must make apprpriate allowance.
Phillips have some good booklets for their cores, or experiment, 1
tip, avoid flyback converters they are far harder to get working
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