Patent ID: 7679942
Filing Date: 2010-03-16
Classification: H02M,Y02B

Abstract:
1. A step-down DC-to-DC converter comprising: an input terminal; an output terminal; a switching circuit connected between the input terminal and the output terminal and configured to reduce an input voltage down to a predetermined voltage and to output the predetermined voltage from the output terminal, the switching circuit including: a rectifying transistor including a P-type transistor and connected in series between the switching transistor and a common ground, wherein a gate of the rectifying transistor is connected to and controlled by a voltage at a connection point that is between the switching transistor and the rectifying transistor; a synchronous rectifying transistor connected in parallel to the rectifying transistor and configured to receive an external control signal through a control electrode thereof so as to perform a switching operation in a manner complementary with the switching operation of the switching transistor; and a drive control circuit configured to cause the synchronous rectifying transistor to turn on when the external control signal represents an instruction of a synchronous rectifying mode and to cause the synchronous rectifying transistor to turn off into a cutoff state when the external control signal represents an instruction of a non-synchronous-rectifying mode.