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From: email@example.com (Bob Wilson)
Subject: Re: multiple flybacks in parallel
Date: Fri, 15 Nov 2002 06:48:01 -0000
Organization: Your Organization
X-Newsreader: WinVN 0.99.9 (Released Version) (x86 32bit)
In article , firstname.lastname@example.org says...
>"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
>> >> > 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
>> >> > supply to try to control the others. The load on all supplies is
>> >> >
>> >> > My gut tells me not to try this, but in theory I guess it could
>> >> > 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
>> 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.
Yes indeed: Right on the hairy edge between discontinuous and continuous
mode. It has many advantages (especially for single-stage PFC flybacks of
moderate power output).
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