Patent attributes
A switching power supply is provided which keeps constant, even when the oscillation frequency of a switching element increases, the on duty of secondary current passing through a secondary winding, thereby achieving a constant current drooping characteristic with high accuracy. To be specific, a secondary current on-period detection circuit generates a signal indicating the off timing of the secondary current, based on a flyback voltage generated on an auxiliary winding. A secondary-current detection delay time correction circuit generates a signal indicating a time when a predetermined period has elapsed since the switching element is turned off. A secondary current on-duty control circuit generates a clock signal for turning on the switching element so as to keep constant the on duty of the secondary current, based on the signal generated by the secondary current on-period detection circuit and the signal generated by the secondary-current detection delay time correction circuit.
