Ferrite core

Abstract

A ferrite core for the use of a power transformer and/or a choke coil with small size has been found. The core is assembled by a pair of identical core halves (21) together with a bobbin (31) wound a coil. Each of the core halves (21) has an E-shaped structure with a center core (23) on which a coil is wound, a pair of side legs (24) and a base plate (22) which couples the center core (23) with the side legs (24). The cross section of the center core (23) is not circular nor rectangular, but is flat having rectangular portion with a first side (2a) and a second side (b-2a) and a pair of arcs coupled with said first side. The diameter (2a) of the arc is the same as the length of the first side. The transformer is mounted on a printed circuit board so that the axis of the center core (23) is parallel to the printed circuit board. Thus, the height (H) of the transformer is low as compared with that of a prior transformer which has a circular center core. Further, because of the smooth arcs at the corners of the center core, the coil wound on the center core is not damaged, and the coil fits well with the core, resulting the reduction of the undesirable leakage inductance of the transformer.