40 W FLYBACK TRANSFORMER - Which core is best to keep low the leakage inductance?

[edaenrico]

Hi,

I have to design a 40 Watt Flyback transformer.


SPECS
-------
1. Primary 230 VAC
2. Secondary 12 Volt
3. Pout = 40 Watt
4. Creepage distance = 6.4 mm
5. Primary inductance = 500 uH
6. Secondary winding = sandwhiched inside the 2 primary halves

QUESTION 1
-------------
Which core is best to keep the Leakage inductance below 1%?


QUESTION 2
-------------
Is this formula correct?

https://www.slideshare.net/Magnetica/seminario-2008-stefano-presentation
See page 23

This is the formula of the Leakage inductance as a function of the geometry of the coil former.


Thanks,
Enrico Migliore

 

[Krithik]

Hi Enrico,

The Core which is having the low window area is correct for low leakage inductance.

For your application PQ2620 is the best core with leakage inductance. but it should have some free space between bobbin and core. I mean to say number tunrs should be less.

I hope this will useful for you

 

[edaenrico]

Hi,

are you sure about low leakage inductance of core PQ2620?

Take a look at this Fairchild's Reference Design: https://www.fairchildsemi.com/support/referencedesign/docs/RD-342.pdf

The leakage inductance is 20 uH and the primary is 600 uH

That means 3% of the primary which is very bad.

Enrico Migliore

 

[Krithik]

Ya Am sure.

But 5% is also ok for lower power applications.

But you should use Clamper diode in your snubber ckt. It will protect the mosfet from peak voltages.

 

[tantudaisu]

Check this link:

Fill the required windows with your parameters and press "Transformer Data" button. You will get several transformer core options for your design.

- tantudaisu -

 

[edaenrico]

Hi,

the leakage inductance depends on how well you build the transformer.

That page helps you choose the right core.

Enrico Migliore