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From: Robert Baer
X-Mailer: Mozilla 4.75 [en] (Win98; U)
Subject: Re: My flyback experiment is on the web
Date: Tue, 15 Oct 2002 06:19:42 GMT
NNTP-Posting-Date: Mon, 14 Oct 2002 23:19:42 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
Chris Carlen wrote:
> Hi folks:
> Here is the URL to my web page showing the results of my most recent
> experiments with a flyback converter. I still haven't gotten a PWM chip
> hooked up yet, as my first goal was to buy some inductors that look like
> they are designed for switching supplies, and see if they'd work better
> than the hand wound transformer I made from a PC power supply core.
> Actually, the inductor seems a bit worse :-(
> All the details are on the web page.
> My main question is why does the inductor get so warm? I figured I
> wasn't really pushing it too hard, so it shouldn't loose much power.
> but it seems most of my losses are occurring in the inductor. I was
> hoping to avoid complex topologies such as a two transistor flyback,
> which requires a transformer, but lends itself to easily shunting the
> remaining core energy back to the input rail. Can that be done with the
> simple flyback that I am working with? I figured I could get 75% or
> better, so I'm not really far off. But I don't like heating the
> inductor, and I want to push up the power another 25% from what I'm
> testing at before I finish.
> I have a smaller inductor, and a larger one too, but all of the toroidal
> type, designed for 150kHz switchers.
> Comments appreciated on what steps I might take to make this simple
> circuit move in the direction of something worth committing to FR-4.
> I will put more on the web page when I get to testing out the PWM chips,
> Good day!
> Christopher R. Carlen
> Suse 7.3 Linux 2.4.10
Inductor heating usually is due to IR losses; you are running too much
current thru the wire.
If it has a core, it is also possible that overdrive (saturation) and
frequency in the loss ergion of the core are other possible loss aeras
(mentioned in order).
Toroids are not for flyback supplies; get an E-I, U-I or pot core and
gap it with grocery bag plastic (0.5 mil is thinnest) or other plastic
sheet (up to 3 mils).
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