Control switch for synchronous rectification circuit of DC-DC converter

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 said 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;
• and
• 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, wherein
• said current transformer is a saturable current transformer, said saturable current transformer comprising a diode for applying the induced voltage in the secondary winding of said saturable current transformer to the gate of said flywheel side FET.

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 a secondary side of said transformer being applied to a source of said commutating side FET;
• a saturable current transformer in which a secondary winding on a secondary side and a tertiary winding on the secondary side are connected to each other in series;
• a diode for applying an induced voltage in the secondary winding on said secondary side of said saturable current transformer to the gate of said flywheel side FET;
• and
• a transistor for applying an induced voltage in the tertiary winding on the secondary side of said saturable current transformer to a base to turn on the transistor when said flywheel side FET turns off, and for discharging electric charges of an input capacitance of said flywheel side FET.