Re: Flyback circuits ?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jan Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>

> I constructed a push-pull type circuit for my flyback experiments today. I am
> gettin much less voltage than with the single transistor circuit. Is this
> normal? If not, any ideas what I have going on?

Flyback is not push-pull. These are two different switching
power supply topologies that differ in some ways. Flybacks store the
energy in the specially-designed air gap of the ferrite core. The longer
the on-time of the transistor, the more energy will be stored, and the
higher the voltage & energy delivered on the secondary during the
transistor off-time.

For flyback, you generally want more than 50% duty cycle, maybe 90%.
Push-pull is just one transistor too many - the extra transistor is equal
to doubling the drive freq of flyback (at least in this case).

You can still continue with push-pull, but then you should keep the
on-times of each transistor at <45% of their maximum on time (which
is 50% of the full cycle). Ok maybe sounds complicated... but, with a
dual output PWM IC you probably already are using this won't be a problem.

Good luck!

cheers,

 - Jan

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