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From: Lund-Nielsen, Jorgen on 1 Jul 2010 06:02
Michael schrieb:
> I have a planar transformer primary winding that has 0.2mm x 10mm
> cross-section (two windings in parallel, actually, top and bottom of
> the PCB; ). It is running at ~450kHz (main harmonic skin depth is
> ~0.1mm). The thickness of the winding should be well utilized (~50%
> duty cycle).
> How about the width? How is current distributed across planar
> transformer winding (width>>skin_depth)?
>
> Little bit of explanation is probably needed.
> The previous version of the same winding was thicker (~1mm) and had
> narrow slot cut in the middle (lengthwise) to make the winding look
> more Litz-like.
> I respun the board to try differentt MOSFETs and changed the winding
> size (made it thin) so it may be laser-cut (as opposed to machined).
> The efficiency went down by 5% or so. Oooops!
> New winding DC resistance is 4mOhm (AC should be higher, but by how
> much??) - too thin, oops again. I stacked them up (three in parallel)
> - the efficiency did not change appreciably.


Also think about the proximity-effect..

http://en.wikipedia.org/wiki/Proximity_effect_(electromagnetism)


Jorgen
dj0ud
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