From: Chris Carlen
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Subject: Re: Core gapping techniques and general SMPS magnetics stuff
Date: Mon, 16 Dec 2002 05:39:37 GMT
NNTP-Posting-Date: Sun, 15 Dec 2002 21:39:37 PST
John Woodgate wrote:
>>But in a flyback which I will be using for the Nixie clock, there will
>>be high peak flux densities associated with energy storage in the core,
>>so I need to use a smaller Al, balanced against acceptable I2R losses,
>>and winding size. It seems that if there weren't I2R losses, and size
>>and EMI issues, an air core would actually be the best for a flyback.
>>(A superconducting air core inductor!)
> Well, if it's just a single winding, maybe. But a transformer with an
> air core would have far too much leakage inductance.
Certainly. But I have been thinking of a simple inductor here. I am
still deliberating about whether to use a transformer or simply an
inductor. I don't need isolation, and the maximum voltage of 300-350V
is easily tolerable by typical MOSFETs. So, it's pretty much a crap
shoot. If you can tell me some things about why I might choose a
transformer vs. simple inductor for a flyback that doesn't need
isolation, and will be designed to output about 90-350V at up to about
12W, I'd be very interested in hearing some reasoning processes.
>>So I will have to gap my cores. How do you folks gap E-cores for
>>prototype/low volume applications? Obviously it's not that hard to
>>figure out a way, but I'm curious how others do it too. I'll probably
>>cut out some shim material, epoxy it to the outer legs, and hold the
>>halves together gently in a vice until it all sets up. Then I can soak
>>it in acetone later for a day if I want to disassemble it.
> That's how you do it physically, but how do you work out what gap
> thickness you want? It matters A LOT! The traditional method was to use
> 'Hanna curves', but I don't think I've ever seen a Hanna curve for a
The Ferroxcube catalog lists various gap sizes and resulting Al values.
There are also charts that I haven't quite finished figuring out how
to use to do it graphically. But it doesn't seem that difficult. I can
do it a bit by trial and error. Just stick some space in their until I
get the L I want, for the number of turns I want.
Thanks for the input,
Christopher R. Carlen
Suse 8.1 Linux 2.4.19