The essence of the flyback transformer is a coupled inductor, and the storage and release of energy are carried out alternately.
The usual practice for the inductor used as energy storage is to open an air gap. Flyback transformers are no exception.
The effect of opening the air gap is twofold:
1）Control the inductance, the appropriate inductance can meet the design requirements.
The inductance is too large and the energy cannot be charged. If the inductance is too small, the current stress of the switch tube will increase.
2) Reduce the magnetic flux density B.
Assuming that the inductance, current and magnetic material have been determined, increasing the air gap can reduce the working flux density of the inductor to prevent saturation.
After understanding the function of opening the air gap, let's see if there is a flyback transformer that does not open the air gap?
The answer is that there is indeed no air gap. There are roughly three situations in which an air gap does not need to be opened.
A. The actual magnetic core selected is much larger than the actual need.
Suppose you make a 1W converter and you choose an EE50 core, then its saturation probability is basically zero.
There is no need to open the air gap.
B. A powder core magnetic material is selected, including FeSiAl, FeNiMo and other materials.
Because the powder core magnetic material allows the working magnetic flux density to reach 10,000, which is much higher than the 3,000 of ordinary ferrite.
Then through proper calculation, there is no need to open an air gap and it will not be saturated. If the calculation is not done properly, it may still be saturated.
C. Design errors or processing errors.
Post time: Dec-02-2022