a regular transformer

[walid]

Hi
I read this somewhere: "a regular transformer is designed to transfer energy from its primary to secondary and to minimize stored energy."

Can someone please explain how they minimize the stored energy, that is what they do to minimize it?

thanx

[ante]

Hi walid,

I think it should read: “minimize losses”, but that’s just me! ::)

[walid]

what about air gap in which they store energy

[ante]

Well anything stored between the primary and the secondary has to be a loss. What I mean is you would like to get out of the transformer as close the same amount of energy as you put into it, don’t you. ;)

[walid]

What i mean is that the ferrite core transformers like a flyback or the one used in a switched mode power supply has an air gap to stor energy.

[indulis]

Ferrite core transformers sometimes do have a very small gap to prevent saturation and help in reset. In general, the idea with transformers is to NOT store any energy in the core. Leakage inductance, which all transformers have, will store energy in the core, so you want to minimize that with good inter-winding coupling and layer stack-up. Transformers also have copper & core losses. These relate to how big your winding window (how much copper of the best AWG can fit

[ante]

Hi indulis,

I agree, that’s the way I see it too. ;)

[walid]

Hi indulis,

"Transformers" used in flyback converters ARE NOT transformers at all, but coupled inductors, and almost ALL the energy is stored is in the gap.

I'll concentrate on this air gap, what the distance?
and how the energy stored in this gap?
thank you

[indulis]

The gap is not fixed.... can vary. Look at some gapped core data sheets, you will find something called inductance factor (nH/1000turns), typical numbers you'll see are 100, 160 and 250. Each of these has a different gap. To really understand this, and get a feel for how diffeent parameters interact, read a few articles on couple inductor design. The energy is stored in the flux in the gap.