Fujitsu Denso Ltd.

Katsuhiko Nishimura

Kazuo Kobayashi

Yoshiki Kubota

A primary side of a transformer has a switching transistor to on-off control the current flowing in a primary winding on a primary side. A secondary side of the transformer has a commutating side FET to be turned on by applying the induced voltage of a tertiary winding on a secondary side of a current transformer, and a flywheel side FET with the primary winding on the primary side of the current transformer connected thereto in series. The current transformation ratio of the current transformer is small in the initial period when the flywheel side FET is turned on, and then, the current transformation ratio is increased by current controlling means comprising a saturable reactor, a diode or the like.

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Kawasaki, Japan

Katsuhiko Nishimura