Patent ID: 7764519

Claim:
A control circuit for controlling a switching power supply, which switches on and off a switching device therein with a pulse-width-modulation signal at an adjusted ON-period ratio for regulating an output voltage therefrom by a pulse-width-modulation method, the control circuit comprising: an error amplifier circuit configured to compare the output voltage from the switching power supply with a reference voltage and output an error signal; a pulse generator circuit configured to generate a pulse, the period thereof being fixed; and an ON-period adjusting circuit configured to start generating the pulse-width-modulation signal in every cycle in response to the pulse outputted from the pulse generator circuit and adjust an ON-period, for which the pulse-width-modulation signal sets the switching device to be ON; wherein the ON-period adjusting circuit changes the ON-period in response to an output voltage of the error signal outputted from the error amplifier circuit for outputting a desired pulse-width-modulation signal.