Effects of air gaps on winding loss in high-frequency planar magnetics

Lumped gaps incur unacceptably high eddy-current loss in small high-frequency magnetic geometries because of their close proximity to the winding. The problem is studied for four simulated inductor structures, using finite-element analysis. It is shown that distribution of the gaps uniformly around the core, which can be realized by using low-permeability magnetic material, reduces the AC-DC resistance ratio of series-connected windings to about two at large conductor width. Measures to reduce the field nonuniformity, such as arranging the series turns in multiple layers so that the winding window has better aspect ratio, further reduce winding loss. Loss reduction due to more uniform field distribution offsets the loss increase due to multilayer arrangement, at least for a small number of turns.<>