A DC-DC converter includes an ON-timing delay circuit in which, when an ON
signal is output from a power switch driving circuit in a control IC to a
power switch, the ON timing of the power switch is delayed by hindering
the start of the ON operation of the power switch. An early turnoff
circuit is provided in which, during delay of the ON timing of the power
switch, a commutating synchronous rectifier has an ON and OFF switching
operation that is inverse with respect to that of the power switch. A
delay eliminating circuit is provided which promptly stops the delay
operation of the ON-timing delay circuit when detecting the turnoff of the
commutating synchronous rectifier which is caused by a drop in the gate of
a commutating synchronous rectifier. When the delay operation of the
ON-timing delay circuit continues after the turnoff the commutating
synchronous rectifier, a loss caused by the continuation of the delay
operation occurs. The problem can be prevented by the delay eliminating
circuit.
