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Difference between flyback and forward transformer?

antknee

New Member
What is the difference between a forward transformer and flyback transformer?

Thanks,

Antknee.
 

Sceadwian

Banned
Flybacks store energy during the on cycle and release it during the off cycle. Forward transformers transfer energy during the on portion and reset during the off period.
 

crutschow

Well-Known Member
Most Helpful Member
A flyback transformer can be thought of as an inductor with an extra winding. The energy is stored in the inductance of the primary winding during the on time of the drive circuit (similar to a switching regulator) which then is transfered to the output winding when the drive circuit is off. A flyback transformer thus has a net DC current through the windings and the core must be designed to handle this without saturating.

A normal forward transformer connection does not store energy but simply transfers the energy from the input winding to the output winding. For a typical switching converter, the transformer is driven by a push-pull driver or by alternately turning off each half of a tapped primary. There usually is no significant off time for the transformer waveform. This transformer type does not have to handle any significant DC current because of the alternating nature of the waveform.
 

antknee

New Member
I've got that, thanks for the comments. I'm currently choosing some of coilcrafts hexa path transformers. They are designed to be flexible and are essentially 6 coils prewound around a core, with a guide to wiring them in series or parallel to adjust for inductance, DCR, Isat and Irms. It's a good idea, I'll get some forward transformers, rather than flyback.

Regards,

Antknee.
 

Sceadwian

Banned
Crut, I don't mean to pick nits, but as I read it the energy in a flyback converter is actually stored in the gap of the transformer winding, flybacks don't work like normal transformers, I don't well understand the magnetics involved in either though, they're quiet complex. One thing I do know is that flyback transformers are generally only useful for a few specific applications, for general use forward transformers are used, and having flexible taps on the primary/secondary as antknee seems to be homing in on are quiet useful for general use.
 

antknee

New Member
for general use forward transformers are used, and having flexible taps on the primary/secondary as antknee seems to be homing in on are quiet useful for general use.
"Homing in on" is the right term. My first order from coilcraft consisted of me buying tidlers, the second order some blocks and others that don't like my frequency, i'm hoping it is third time lucky.
 

crutschow

Well-Known Member
Most Helpful Member
Crut, I don't mean to pick nits, but as I read it the energy in a flyback converter is actually stored in the gap of the transformer winding, flybacks don't work like normal transformers, I don't well understand the magnetics involved in either though, they're quiet complex.
I learned something new. I didn't realize that the magnetic energy is stored mostly in the air gap(s).

But my statement was correct in that the energy is stored in the inductance of the coil (E = ½LI²), gap or not. The purpose of the gap is to prevent the core from saturating with the DC current, with would otherwise cause the inductance to decrease with current.

Flybacks are not that hard to understand if you just look at them as an inductor storing the energy from the primary and then transferring the energy to the secondary. (Actually during this transfer the transformer does also acts like a transformer with the secondary voltage, as determined by the secondary load, being reflected back to the primary. But during that interval the primary is carrying no current, all the current is going to the secondary output.)
 

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