Control circuit for a switching power supply, method for controlling a switching power supply and computer program

A control circuit for a power supply having a controllable switch for switching a current through a first transformer winding and a voltage providing circuit for providing an output voltage based on a voltage generated in a second transformer winding has a comparing unit for generating a comparison signal. The control circuit has a threshold signal modulation circuit adapted to modulate the threshold signal that the comparison signal is activated as soon as the input signal crosses a first threshold value, if the current flowing through the switch exhibits a first current slope rate, and that the comparison signal is activated as soon as the input signal crosses a second threshold value, if the current flowing through the switch exhibits a second current slope rate smaller than the first rate. For a given voltage, the first threshold is smaller than the second threshold.