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Leakage Inductance

Posted by: Tugay on Tue, 06/08/2021

Hi Friends,

I have designed 32V 7A SMPS using with Pıexpert. According to PIExpert, the transformer's leakage inductance should be 3.5uH, but I measure 7uH in the transformer I designed.

1. Is this a big problem for transformer design?

2. Will this problem prevent the circuit from working?

3.What kind of problems does a high leakage inductance cause?

4.The most important question is will the TOP259EN be damaged?

Thanks,

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Submitted by PI-Ayel on Fri, 06/18/2021

Hi Tugay,

 

The leakage inductance is an estimation. Ideally, you want your leakage inductance to be as small as possible. This is not a big problem for the transformer design (1) and your circuit should still work (2). However, you should be mindful of the drain-to-source voltage ringing as higher leakage inductance means higher VDS ringing (3), and higher VDS ringing may exceed the breakdown voltage of your TOP259EN. Start by powering up on your lowest voltage and gradually increasing it to make sure that primary VDS doesn't reach its BVDSS, and give it some 90% margin. Apart from safety issue, the higher leakage inductance can also lead to a lower efficiency so you may want to examine that too.