A Performance Evaluation of Shaped Planar Inductor Windings in Gapped Core Applications Utilizing Turns With Constant DC-Resistance

AC-losses in gapped-core planar inductor windings seem to be dominated by eddy losses induced by the time varying fringing flux near the air gap. Shaping the windings in the region of the gap reduces AC-losses but the reduction in width of planar foil conductors causes the DC-resistance to increase. The winding shape can be optimized using FEM-tools but the process is very time consuming. If the DC-resistance of the conductors is however kept constant by increasing its thickness a reduction in the AC-losses occurs continuously as the conductor tips are moved away from the gap. The optimum notch radius can now be predicted easily and is governed mainly by the geometry of the winding stack and core window. The predicted results are verified for a specific inductor design using a calorimetric experiment.