Abstract: Provided is an annular reactor core formed of a U-shaped core and core legs. Core joints including end portions and two protrusions form the U-shaped core. Between the protrusions of these core joints, a plurality of (two) core legs 6 formed of core blocks are arranged so as to have gaps and the protrusions. The ratio A/B, which is a ratio of the length A of the protrusions of the core joint to the average length B of the core blocks constituting the core legs in a magnetic path direction, is optimized so as to be not less than 0.3 but not more than 8.0, whereby an increase in copper loss due to leak magnetic fluxes of the gap portions is suppressed.

Abstract: Provided is an annular reactor core formed of a U-shaped core and core legs. Core joints including end portions and two protrusions form the U-shaped core. Between the protrusions of these core joints, a plurality of (two) core legs 6 formed of core blocks are arranged so as to have gaps and the protrusions. The ratio A/B, which is a ratio of the length A of the protrusions of the core joint to the average length B of the core blocks constituting the core legs in a magnetic path direction, is optimized so as to be not less than 0.3 but not more than 8.0, whereby an increase in copper loss due to leak magnetic fluxes of the gap portions is suppressed.