Planar inductors using NiZn ferrite thin plates and the application to high-frequency DC-DC converters

New structure planar inductors are developed for miniaturized DC-DC converters. A thin gap is introduced into the sandwich-structured planar inductors between a pair of magnetic plates, in one of which a meander coil is embedded. Due to the thin air gap introduced, the flux density in the magnetic plates becomes uniform, resulting in low iron loss. Planar inductors using NiZn ferrite thin plates are successfully applied to a 10-W-class buck converter operated at 2 MHz. The efficiency is higher than 82%, and the effective volume of the inductor is 0.2 cm ³ (1 cm square and 2 mm thick)