flyback converter and airgap

[sunil21]

when we design a flyback , we calculate inductance etc... then calculate the airgap.
For instance lets say the calculated inductance is 380 micro henry and airgap is .25mm and ''X'' no of turns.
But I have a core with .5mm airgap (from source).
So then just by finding the AL value of the gapped core recalculate the the turns and its ratio?
(as said in 'Power supply cookbook')
what is the negative and positive side of this increased gap.?

 

[cupoftea]

Yes.....just calc for the new gap...the core shoudl give you an AL value.
..or just find it by winding it with some turns and measure L.
A big gap in theory means more noisy...but dont worry too much as 0.5mm is still small....as long as your peak B is not >310mT.
Also, as long as the gap is less than 10%, say, of the centre leg length.

 

[Easy peasy]

B = Uo.Ur.I.N/Lg, for air gap Ur = 1, you know Ipk, N, and Lgap.

any design should have a Bpk that is commensurate with operating freq and desired losses.

 

[cupoftea]

you can also download the free MDT tool from TDK to get the AL value for a given gap length in a standard core shape.