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From: "Harry Dellamano"
Subject: Re: multiple flybacks in parallel
Date: Wed, 13 Nov 2002 20:27:34 -0800
Organization: Posted via Supernews, http://www.supernews.com
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"Bob Wilson" wrote in message
> In article , email@example.com
> >"Roy McCammon" wrote in message
> >> Steve Denning wrote:
> >> >
> >> > I am working on an application where I need 6 low power
> >> > each) but each output must be isolated from each other. I'm required
> >> > existing magnetics to create the supplies. Rather than build 6
> >> > supplies I am wondering if I could use one PWM chip and MOSFET and
> >the 6
> >> > flyback transformer primaries in parallel. I would get feedback from
> >> > 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.
> >> > anyone tried this? What would the risks be?
> >> The flyback stores energy in the primary during one part
> >> of the cycle and transfers it to the secondary during the
> >> other part of the cycle. You vary the total power
> >> transferred
> >> by varying the energy stored in each cycle, or varying
> >> the number of cycles per second. Each of your transformers
> >> will see the same cycle time and frequency, so the energy
> >> transferred will be inversely proportional to the primary
> >> inductance. How well do the inductances match?
> > Hey Roy, that is only true in discontinuous mode of operation. In
> >continuous mode you must use a single transformer with multi output
> >windings. In continuous mode and multi transformers the delta Ip are
> >but the DC components will not balance.
> ...but you have the fun of trying to compensate for the right half-plane
> zero that is inherent with a continuous mode flyback. This can reduce tour
> loop bandwidth so much that transient response may be unacceptable.
So true Bob, that's why Critical Conduction Mode is the best of all worlds
in flyback topology.
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