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i am designing a transformer for 2-switch forward converter. For now, primary is wound as 5 wires of 0,5mm diameter (34 turns, 3 layers), the secondary is wound as 3 wires of 1,32mm diameter (17 turns, 2 layers). The frequency of smps is 83khz. The idea is to use litz wire in primary and secondary and increase frequency to 100khz. So, the primary would be wound as litz wire (0,1mm diameter, 120 strands) in 2 layers. The secondary would be litz too (0,071mm diameter, 1076 strands) in 2 layers too. So, the skin effect must be elliminated completely. But what about a coupling? I have read a lot of books on winding interleaving technique, but all the cases if wire radius is more or less greater than the skin depth. So, it is easy to do interleaving on this litz wire transformer (1 layer primary, 1 layer secondary, 2 layer primary, 2 layer secondary). So guys, will it worth it? I hope there must be some benefits like increased coupling between windings and reduced proximity losses... But i am not sure about that. So - is it good idea to use winding interleaving on litz wire windings? Will i get better coupling between windings and decreased leakage inductance? Thanks for your response. It is easy to do interleaving, but harder than just wound windings as 1P,2P,1S,2S. I will post results of my experiments most likely.

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  • \$\begingroup\$ Also consider a bobbin that allows a bundle winding gap e.g 6 turns gap 6 turns gap... repeat to raise SRF as required. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 5 '18 at 5:49
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It is better to do interleave winding method to reduce the number of consecutive layers with rising MMF proximity losses towards centre of core.

Since your turns ratio is 2:1 this is what your interleave pattern should be 2P1S... repeating.

If Eddy current proximity losses can be minimized, the benefit is lower core temp rise at rated current.

There are many variables with core types , geometry and winding methods and skin depth becomes more important as the number of layers increases.

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  • \$\begingroup\$ sounds good, but the transformer has different current ratio: the primary conducts 3A of current while secondary conducts 10A. So, it is impossible to do interleaving as you said. \$\endgroup\$ – silkyre6xtenz Mar 5 '18 at 7:28
  • \$\begingroup\$ Then add insulation between all layers to reduce interwinding proximity flux \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 5 '18 at 12:53

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