Hybrid integrated circuit planar transformer

A planar transformer comprising in combination:

• (a) a printed circuit board having parallel first and second surfaces;
• (b) a first spiral winding on one of the first and second surfaces surrounding a first magnetic flux path area, and a second spiral winding generally concentric with the first spiral winding on one of the first and second surfaces surrounding a second magnetic flux path area that overlaps the first magnetic flux path area, a portion of the printed circuit board with the first and second spiral windings thereon having a maximum thickness;
• and
• (c) a ferrite core assembly including
• i. a first core section including a thin, flat first plate,
• ii. a second core section including a thin, flat second plate, spaced thin, flat, elongated first and second post sections disposed between the first and second plates abutting inner surfaces of the first and second plates, forming a shallow gap greater than the maximum thickness bounded by the first and second post sections and inner surfaces of the first and second plates, the portion of the printed circuit board with the first and second spiral windings thereon extending entirely into the shallow gap so that magnetic flux passing through the first and second magnetic flux path areas also passes across the gap.