From: Chris Carlen
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Subject: Re: My flyback experiment is on the web
Date: Tue, 15 Oct 2002 02:52:59 GMT
NNTP-Posting-Date: Mon, 14 Oct 2002 19:52:59 PDT
Bob Wilson wrote:
> Your inductor gets warm for one of two reasons:
> 1. It is an el-cheapo, lossy iron core inductor (these are very common),
> which was never designed for what you are using it for. These types of
> inductors are designed for power filtering, where there is a relatively
> small amount of current ripple, superimposed on DC. Their hysteresis losses
> at any reaonable frequency are far to high to me useful as a SMPS inductor.
> 2. Your copper losses are too high (wire gauge is too small).
> The problem is undoubtably due to 1. above. Using an inductor that "looks
> like it is designed for switching supplies" is probably your big problem.
> You need to DESIGN the thing, use core material that is intended for what
> you want it to do. Also, forget about using a toroidal inductor, It isn't
> worth the time and expense. It makes far more sense to design an inductor
> around a ferrite E-E. or RM, or ETD core, whose type of ferrite does what
> you want. Those cheap iron-core toriods are useless for what you are doing.
> A simple flyback cannot return leakage energy back to the bulk storage cap,
> like the 2-transistor flyback can. It has to be dissipated in snubbers. But
> big deal! All you will lose is a couple of percent of efficiency if you
> design the thing right, so it is hardly worth worrying about.
Thanks for the input, Bob.
Ok, I give in. I called a nearby distributor for Fair-Rite magnetics
today, and they sell handfulls of cores. So I will select a few type 78
material cores to play with. That is their lowest loss stuff for power
applications. Looks like only a few 100mW per cm^3 in the 50-100 kHz
range. I'll just buy the best 78 stuff instead of thinking of
compromizing on 77 because this isn't for production. I'd like to see
what the best core can do.
Christopher R. Carlen
Suse 7.3 Linux 2.4.10