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From: "Graham Holloway"
Subject: Re: multiple flybacks in parallel
Date: Wed, 13 Nov 2002 18:17:56 -0000
NNTP-Posting-Date: Wed, 13 Nov 2002 18:17:22 +0000 (UTC)
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"Steve Denning" wrote in message
> I am working on an application where I need 6 low power outputs(approx
> each) but each output must be isolated from each other. I'm required to
> existing magnetics to create the supplies. Rather than build 6 seperate
> supplies I am wondering if I could use one PWM chip and MOSFET and put the
> flyback transformer primaries in parallel. I would get feedback from one
> supply to try to control the others. The load on all supplies is the
> My gut tells me not to try this, but in theory I guess it could work. Has
> anyone tried this? What would the risks be?
Go ahead with your idea. There isn't really a problem. I am assuming that
all the transformers are similar and therefore the outputs will all
generally track one another through normal transformer action. There will be
a small problem if one or more of the outputs becomes unloaded, the worst
case being no load on the five remaining outputs that have no feedback
signal from them. Stored energy will then want to find a place to dump
itself. If there is an RCD clamp on the switching MOSFET, ensure the clamp
can absorb this energy. You might wish to add a power zener (~5W) to each
output as an alternative clamp. Good luck.
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