The transformer section in Flyback converter

[NexusN]

Homework Statement

Hi everyone,
I am now studying the Flyback converter as a component in a SMPS,
my question is on the transformer unit on the converter.
There are Primary side and Secondary side in the converter,
at any given moment only either of the sides conducts, that is, when Primary conducts, Secondary doesn't.

From the book I am reading now, on switching to the OFF state, huge spike can arise as a result of the leakage inductance.
Does it mean, if we assume perfect coupling and neglect the effect of leakage inductance, we can actually strictly cut the current in the primary side from a finite value to zero without causing a spike, as the energy is free-wheeled via the secondary circuit?
Thank you.

Homework Equations

The Attempt at a Solution

 

[uart]

Does it mean, if we assume perfect coupling and neglect the effect of leakage inductance, we can actually strictly cut the current in the primary side from a finite value to zero without causing a spike, as the energy is free-wheeled via the secondary circuit?

Yes it does.

We often think in terms of "not being able to change the current in an inductor instantaneously", but more fundamentally it's about not being able to change the magnetic flux instantaneously. In the flyback transformer the flux that was produced by the primary current is maintained by the secondary current after switching, so there's no discontinuity.

It's important to realize that this makes a flyback transformer a very different beast compared to a normal voltage transformer, as the flyback tranny takes 100% of the load current through the magnetizing branch (compared with say 1% in a normal transformer). For this reason a flyback transformer is designed more like an inductor than a traditional transformer.

 

[NexusN]

Yes it does.

We often think in terms of "not being able to change the current in an inductor instantaneously", but more fundamentally it's about not being able to change the magnetic flux instantaneously. In the flyback transformer the flux that was produced by the primary current is maintained by the secondary current after switching, so there's no discontinuity.

It's important to realize that this makes a flyback transformer a very different beast compared to a normal voltage transformer, as the flyback tranny takes 100% of the load current through the magnetizing branch (compared with say 1% in a normal transformer). For this reason a flyback transformer is designed more like an inductor than a traditional transformer.

Thank you very much for the explanation,:tongue:
I think this is a very important definition I must understand before I can go deeper in SMPS,
I was struggled by the current definition in the past.