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Air gap in SMPS tranformer

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Aug 10, 2009
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why the gap required in forward smps transformer

Dear All,

Please let me know about maintaining air gap in ferrite types of SMPS transformers. Why do we make it so. Is it required in both forward and flyback types of power supplies or only in FB type.

Pleasde clear me this. I would be so greatfull to you.




I'm not so expert in trasformers.. but i can tell you about Flyback trasformer..

They do not work like a true trasf but more like an inductance.
The store energy during mosfet on phase and deliver it during the off phase.

To store energy you can work with current o with inductance (E=1/2LI^2).
The gap is a good way to obtain large L.


air gap transformer

well if you dont put a gap....then your transformer will saturate as the current rises.

when you put a gap, it will not saturate, but the pennance is that you have to wind many turns to get a decent leve of inductance.

importance of air-gap in smps transformer

how the minimum required air gap can be calculated .

what will happen if i got a inductance with more no of turns and without ferrite core.will it work same as the ferrite core transformer?


how to make air gap tranformer

berni80 said:
To store energy you can work with current o with inductance (E=1/2LI^2).
The gap is a good way to obtain large L.

The gap will give you a smaller L for sure. But you can have a bigger I before saturation.

Actually, you need a gapped core for energy storage like in flyback transformers. You don't need a gap in forward transformers, because for a forward, you want the least possible energy in the core.

When you make a gap, and you do the math, you will see that most energy is stored in the gap itself. Energy in the magnetic field = flux^2 * R /2. R = reluctance and since the reluctance of the gap is much bigger than the reluctance of the core, the most eneregy is in the gap.

Find some book on basic magnetics, work out the flux, reluctances, ... I'm sure you will find out.


ferrite air gap


u dont need an Air Gap ,when u using an Forward or push pull design..But u can checked it at the Switching Trace of the MOSFet or ec.Mostly if u put litle AIR GAP in the transformer the Temp of the Transformer get cooler..for example for an ETD core about 0.02mm..


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