A newly developed planar inductor and its application to dc-dc converters are described. The planar inductor consists of a planar spiral coil and soft magnetic sheets, it has a small size (11110.8mm), 33µH inductance and a maximum quality factor of 14. The step down chopper dc-dc converter has been developed by using planar inductor, which has small size (20154mm), 5V-2W typical output and output power/volume ratio of 1.7W/cc. The switching converter can be miniaturized by using the planar inductor.