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

A method for controlling a switching power supply comprising a controllable switch for switching a current flowing through a first winding of a transformer, a voltage providing circuit for providing an output voltage based on a voltage generated in a second winding of the transformer and a switch driver for periodically closing the switch and for opening the switch in response to an occurrence of a condition to open the switch, the method comprising:

• modulating a threshold signal dependent on a voltage present in the voltage providing circuit in such a way that a comparison between the threshold signal and a signal derived from a current flowing through the controllable switch or through the first winding yields a condition to open the switch as soon as the signal derived from the current through the controllable switch reaches a first threshold value, if a current through the switch or through the first winding exhibits a first slope rate, and that the comparison between the threshold signal and the signal derived from the current through the controllable switch or through the first winding yields a condition to open the switch as soon as the signal derived from the current through the controllable switch or through the first winding reaches a second threshold value, if the current through the switch or the first winding exhibits a second slope rate smaller than the first slope rate,
• wherein, for a given voltage present in the voltage providing circuit, the first threshold value is smaller than the second threshold value.

A computer program product comprising a program code stored on a computer readable medium, wherein the program code when executed on a computer performs a method for controlling a switching power supply comprising a controllable switch for switching a current flowing through a first winding of a transformer, a voltage providing circuit for providing an output voltage based on a voltage generated in a second winding of the transformer and a switch driver for periodically closing the switch and for opening the switch in response to an occurrence of a condition to open the switch, the method comprising:

• modulating a threshold signal dependent on a voltage present in the voltage providing circuit in such a way that a comparison between the threshold signal and a signal derived from a current flowing through the controllable switch or through the first winding yields a condition to open the switch as soon as the signal derived from the current through the controllable switch reaches a first threshold value, if a current through the switch or through the first winding exhibits a first slope rate, and that the comparison between the threshold signal and the signal derived from the current through the controllable switch or through the first winding yields a condition to open the switch as soon as the signal derived from the current through the controllable switch or through the first winding reaches a second threshold value, if the current through the switch or the first winding exhibits a second slope rate smaller than the first slope rate, wherein, for a given voltage present in the voltage providing circuit, the first threshold value is smaller than the second threshold value.