From: John Larkin
Subject: Re: My flyback experiment is on the web
Date: Mon, 14 Oct 2002 09:27:18 -0700
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On Mon, 14 Oct 2002 09:58:53 GMT, firstname.lastname@example.org (Nico Coesel)
>Chris Carlen wrote:
>>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.
>Strange; I've designed a similar converter (48V in, 168V / 100mA
>@100kHz) but didn't have problems with the inductors. I've used 2
>newport power filtering 100uH inductors in series (didn't have 200uH
>I see there is also some ringing in your circuit. Did you try to put a
>small snubber accross the drain and ground? Did you also consider
>simulating the circuit?
Snubbing a stepup converter like this will damp the ringing, which
makes the waveforms look nicer, but will generally reduce efficiency
by stealing energy from the initial rising edge. Since the energy
stored in parasitic capacitance must be dissipated somewhere, it
doesn't really matter where; so let it ring.