A Hall element (H) is arranged at an air gap of a choke coil (30). Power
semiconductor elements (P1) and (P2) are attached to a heat radiation
fin (61) directly by soldering. A rectangular-hollow-shaped metal core (27)
is formed by winding a long metal thin plate multiple turns into a rectangular-hollow-shape
and is fitted to a bar shaped ferrite core (26) from outside of the primary
winding (21) and the secondary winding (22). The inner diameter of
one side of the rectangular-hollow-shape core is larger than both outer diameters
of the primary winding (21) and the secondary winding (22) and the
inner diameter of the other side of the rectangular-hollow-shape core is larger
than the height of the primary winding (21) and the secondary winding (22).
The rectangular-hollow-shape (27) core is arranged such that an air gap
(G) exists between the rectangular-hollow-shape core (27) and the bar shaped
ferrite core (26).
