A power supply circuit includes a pre-regulator configured to receive an input voltage and to generate an output voltage, and a switching current regulator coupled to an output of the pre-regulator and configured to regulate a level of current supplied to an output load. The switching current regulator is controlled by a switching signal having a duty cycle. The circuit further includes a controller that generates the switching signal. The controller monitors the duty cycle of the switching signal and controls a level of the output voltage generated by the pre-regulator by providing a control signal in response to the duty cycle of the switching signal.