Planar inductors with a new coil configuration (abstract)

High frequency (f≥1 MHz) magnetic power devices are key elements for developing compact and low profile switching power supplies. Planar inductors with a flat coil are investigated,^1-3 however, a problem arising from the use of a flat coil is not addressed. The problem is that normal components to the magnetic plate inevitably exist in the exciting fields from a flat coil and that those components induce severe in plane eddy currents. The problem is most typical in the case of a spiral coil. In this paper, a new flat coil is proposed (see Fig. 1) for planar inductors which greatly improves the problem because paths of eddy currents are chopped up corresponding to the mesh size of the coil. It is obvious that density of eddy currents becomes small when the mesh size becomes fine. Sandwich planar inductors with a proposed coil (mesh coil) and a meander one were prepared for preliminary tests using pairs of Metglas 2705M amorphous ribbons of 50×50 mm² and 100 μm copper wires, where the mesh size was 3 mm, equal to the pitch of the meander coil. Inductances at 1 MHz were 1.85 μH for the mesh coil and 2.25 μH for the meander one, whereas Q_max=5 at 6 MHz for the mesh coil and 4.5 at 2 MHz for the meander one. Advantages of the mesh coil may further become clear when it is made on the magnetic plates with thin insulating layer in between by IC or thick film process.