Patent ID: 6879499

Claim:
A DC-DC converter comprising: a transformer having a primary side and a secondary side; at least one power switch provided on the primary side of said transformer, a switching operation of said at least one power switch causing the secondary side of said transformer to output AC power; a rectifying-and-smoothing circuit connected to the secondary side of said transformer and converting the output AC power into DC power, said rectifying-and-smoothing circuit including an inversely driven synchronous rectifier including a MOSFET having an ON/OFF switching operation that is inverse with respect to that of said at least one power switch; a power switch driving circuit for alternately outputting an ON signal and an OFF signal to said at least one power switch in order to control the switching operation of said at least one power switch; an ON-timing delay circuit for detecting output of the ON signal from said power switch driving circuit to said at least one power switch and delaying ON timing of said at least one power switch by hindering the start of an ON operation of said at least one power switch based on the ON signal; an early turnoff circuit for turning off the inversely driven synchronous rectifier by outputting an OFF signal to said inversely driven synchronous rectifier upon detecting output of the ON signal from said power switch driving circuit to said at least one power switch, in a period in which the start of the ON operation of said at least one power switch is delayed by said ON-timing delay circuit; and a delay eliminating circuit for eliminating a delay operation of said ON-timing delay circuit when detecting turnoff of the inversely driven synchronous rectifier by detecting a decrease in the gate voltage of the inversely driven synchronous rectifier.