Air gap technique in transformers

[iamdnpkc]

this is phani kumar. i am working on designing of SMPS and led drivers.

i have a query regarding air gap in transformers.

Different techniques of air gap in transformers:
1) keeping some milar sheet as an air gap.
2) cuting some part of 1 core.
3) Cutting both cores.

please suggest me , which one is better and if possible please explain the same.

 

[cl10greg]

Air gap and core is dependent on the power and efficiency you are seeking. The principle of mutual inductance, the alternating magnetic field you are creating and the distance all play a part. You would need to look at your systems need to determine what is the best option. I don't understand what you mean by cutting cores. In general, a common core is better because of the inductance induced in the ferrous material increases the amount of power.

 

[iamdnpkc]

thanx for the reply.

here is some explanation:

when we design a flyback transformer, we cant get directly our required Primary inductance(Lp), without keeping Airgap.
in india, Normally vendors use some milar sheets to get air gap b/w cores.
but when we get them china, they use other technique like they will reduce the dimension of one core such that the air gap is achieved.
Like wise , they will reduce the dimension of 2 cores such that the air gap is achieved .

And now my question is, in this 3 techniques , which one is better ???
1) Keeping extra milar sheet inbetween 2 cores .
2) reducing 1 core size.
3) reducing 2 cores sizes.


i hope you understand my query.

 

[FvM]

There's no real difference between 2) and 3). Catalog products are usually combining an ungapped with a gapped core halve.

Case 1) involves larger stray field, higher transformer leakage inductance and most likely additional eddy current losses.

 

[chuckey]

Using Mylar is by far the cheapest way. "cutting" transformer cores actually means grinding them very accurately, Mylar is mass produced to a good tolerance.
Frank

 

[aashitech]

thanx for the reply.

here is some explanation:

when we design a flyback transformer, we cant get directly our required Primary inductance(Lp), without keeping Airgap.
in india, Normally vendors use some milar sheets to get air gap b/w cores.
but when we get them china, they use other technique like they will reduce the dimension of one core such that the air gap is achieved.
Like wise , they will reduce the dimension of 2 cores such that the air gap is achieved .

No...in India also many vendors stock pre gapped cores with specific AL values...so if you want the pre-gapped core then ask those vendors about which gapped cores in which geometry they regularly have in stock...and then you can design your magnetics/transformers accordingly.
If you can order in some good quantities then vendors may arrange your required air gap in target core(s).

 

[FvM]

I agree that a spacer is the cheapest way to provide an air gap. You have to check if the transformer performance is sufficient for your requirements.

 

[iamdnpkc]

Dear All,

thanx for your suggestions and explanations .