Patent ID: 7906942

Claim:
A control circuit that controls a DC-DC converter of a synchronous rectifier type including an inductor or a transformer, the control circuit comprising: an ON-period decision part that determines whether an ON-period of a synchronous rectifier switch of the DC-DC converter is too long or too short; an ON-period adjustment part that generates an adjusting signal to adjust the ON-period during which the synchronous rectifier switch is ON based on a decision of the ON-period decision part; and a first delay part that adjusts a length of a delay from a first time, when a rectifier changeover signal, which changes the synchronous rectifier switch between ON and OFF states, turns the synchronous rectifier switch on, to a second time, when the rectifier changeover signal turns the synchronous rectifier switch off forcibly, wherein the first delay part comprises: a third current source that outputs an output value that varies according to the adjusting signal, the third current source comprising a FET including a gate to which the adjusting signal is fed, a third switch that changes the third current source between ON and OFF states based on a first changeover signal, a second capacitor connected between the third switch and ground, a fourth switch that connects a connecting point of the third switch and the second capacitor to ground based on a second changeover signal, a fourth logic part that generates, using an input signal of a drive circuit of the synchronous rectifier switch as an input thereof, the first changeover signal and the second changeover signal, and a fifth logic part that generates an output signal that forcibly turns off the synchronous rectifier switch based on a voltage across the second capacitor.