Patent ID: 6430063
Filing Date: 2002-08-06
Classification: H02M,Y02B

Abstract:
A synchronous rectification circuit of a DC-DC converter comprising:a switching transistor for on-off controlling a current flowing in a primary winding on a primary side of a transformer; a commutating side FET for being on-off controlled by an induced voltage in a tertiary winding on a secondary side of said transformer being applied to a gate of said commutating side FET, and an induced voltage in a secondary winding on the secondary side of said transformer being applied to a source of said commutating side FET; a current transformer in which a drain of said commutating side FET is connected to one end of a primary winding on a primary side; a flywheel side FET for being on-off controlled by the other end of said primary winding on the primary side of said current transformer being connected to a drain of said flywheel side FET, and an induced voltage in a secondary winding on a secondary side of said current transformer being applied to a gate of said flywheel side FET; and current controlling means for setting a current transformer ratio of said current transformer to be a first value during an initial period when said flywheel side FET is turned on, and for setting the current transformation ratio of said current transformer to be a second value after said initial period has elapsed, wherein said second value is larger than said first value.