How many strands for windings in smps transformer?

[grizedale]

Page 22 (LHS) of the following states that for smps transformers above 50KHz, strands of windings should be no wider than 0.07mm


https://www.ferroxcube.com/prod/assets/sfappl.pdf


..surely that can't be right?

..it would mean huge numbers of strands?

 

[FvM]

Of course it is right. But look sharp. The respective part is about high Q signal inductors and transformers, not power inductors. Litz wire is strongly suggested to achieve highest Q. Litz wire - Wikipedia, the free encyclopedia

Also high frequency power magnetic components take advantage from litz wire, particularly for low voltage/high current windings, but mutiple strands of medium gauge enamelled wire are often sufficient. It's useful to have an idea of the AC resistance increment of a specific wire diameter to decide about litz wire or multi strand. The epcos Ferrite tool calculates a factor for specific winding geometries, based on skin and proximity effect. **broken link removed**