A planar transformer includes: a primary side planar air core coil; a secondary side planar air core coil; a primary side planar core; and a secondary side planar core. The secondary side planar air core coil is arranged so as to be spaced from the primary side planar air core coil in the winding center axis direction of the primary side planar air core coil, the secondary side planar air core coil having a non-facing portion configured not to face the primary side planar air core coil in the winding center axis direction. The primary side planar core and the secondary side planar core are stacked on outer sides of the primary side planar air core coil and the secondary side planar air core coil in the directions of the winding center axes, respectively.

A planar transformer includes: a primary side planar air core coil; a secondary side planar air core coil; a primary side planar core; and a secondary side planar core. The secondary side planar air core coil is arranged so as to be spaced from the primary side planar air core coil in the winding center axis direction of the primary side planar air core coil, the secondary side planar air core coil having a non-facing portion configured not to face the primary side planar air core coil in the winding center axis direction. The primary side planar core and the secondary side planar core are stacked on outer sides of the primary side planar air core coil and the secondary side planar air core coil in the directions of the winding center axes, respectively.

A resonant high current density transformer including two cores that are abut against each other with their first and second side posts on two sides thereof. A first bobbin envelops the first side posts on the same side of the two cores. A side plate is provided on either end of the first bobbin. The space between the two side plates is divided into two coil slots with a spacer, and at least a wire is wound in each coil slot to form a primary winding. A further second bobbin envelops the second side posts on the same side of the two cores. The outer periphery of the second bobbin is divided into two winding regions by another spacer, and a metal plate envelops each of the winding regions to form a secondary winding. A bobbin mount is disposed at the external flank of the second bobbin with a barrier plate at a side thereof for separating the first and the second bobbins. An insulating separating cover is provided on a side of the first bobbin closer to the bobbin mount, and the two ends of the separating cover cover the top and bottom sides of the first bobbin, respectively.

A resonant high current density transformer including two cores that are abut against each other with their first and second side posts on two sides thereof. A first bobbin envelops the first side posts on the same side of the two cores. A side plate is provided on either end of the first bobbin. The space between the two side plates is divided into two coil slots with a spacer, and at least a wire is wound in each coil slot to form a primary winding. A further second bobbin envelops the second side posts on the same side of the two cores. The outer periphery of the second bobbin is divided into two winding regions by another spacer, and a metal plate envelops each of the winding regions to form a secondary winding. A bobbin mount is disposed at the external flank of the second bobbin with a barrier plate at a side thereof for separating the first and the second bobbins. An insulating separating cover is provided on a side of the first bobbin closer to the bobbin mount, and the two ends of the separating cover cover the top and bottom sides of the first bobbin, respectively.