Top 249YN Power supply 5V8A

it appears you have too little coupling between windings on your transformer, i.e. too great a leakage inductance.

Hi ! Easy Peasy.
Can you tell me some methods that provide reducing leakage inductance?
In my power supply, I just used one method like " sandwiched transformer construction".

Can you tell me how to calculate or measure leakage inductance?

Hi tonycnbel,

You can measure inductance with the use of an LCR meter (same procedure when you measured the 600uH primary inductance). But in this case, you need to short all the other windings (i.e 12V winding, 5V winding, VCC winding).

To reduce leakage inductance, try to use sandwiched construction and minimize insulation thickness in between layers. If possible, minimize the number of layers.

Best Regards,
PI-Seven of Nine

Hi, PI seven of nine
Thank a lot for answering me . I try your solution and get the result that Lleak was 30uH. Do you think it's High?
And I put some air gap in ferrite core before, may it do effect on Lleak?
Best Regards,

air gap has no effect, you need a 3 or 5 layer construction, Pri-Sec-Pri etc ... a longer bobbin on a slightly bigger core will help too

Hi tonycnbel,

Air gap has no effect. If you gap it while maintaining same number of turns, this will result to lower inductance. You might end up increasing the number of turns just to arrive on the required inductance of the design. Increasing the number of turns might result to additional layers that can increase the leakage.

At 30uH leakage inductance with 600uH magnetizing inductance, this is around 5% which is already low. But if you can still reduce, the better. 3% to 5% is already considered low.

Thanks,
PI-SevenofNine