Generated are an error signal representative of a difference between a signal representative of the output voltage of a current mode switching power supply and a reference voltage, and a peak current threshold signal that is indicative of a peak current that should be reached in an inductor within the power supply during each cycle of a periodic clock signal and that has a level that is based on the error signal. A switch control signal regulates the voltage output of the power supply by closing and then opening a power switch during each cycle of the periodic clock signal. Timing of opening is based on the peak current threshold signal. Negative slope compensation causes the switch control circuit to delay opening the power switch during each cycle of the periodic clock signal in an amount that decreases with increasing duty cycles of the switch control signal.