Patent ID: 7157998

Claim:
A ferrite core having a substantially funnel shape, comprising a plurality of convex portions arranged on an inner circumferential surface in a circumferential direction, wherein all the convex portions have a ridge shape in a direction connecting an end on a small diameter side of the ferrite core to an end on a large diameter side thereof, in a cross-section orthogonal to a center axis of the ferrite core, a cross-sectional shape of an outer circumferential surface of the ferrite core is substantially circular, and in a cross-section orthogonal to the center axis, a cross-sectional shape of an inner circumferential surface of the ferrite core excluding the plurality of convex portions is substantially circular in a vicinity of the end on the large diameter side and is substantially rectangular in a portion between the vicinity of the end on the small diameter side and the vicinity of the end on the large diameter side.