A power converter (14) can include a switching system (18) to convert a direct current (DC) input voltage to an output voltage based on a switching signal having a duty-cycle. A controller (16) can set the duty-cycle of the switching signal, depending on the DC input voltage, to one of a substantially constant value, such that the output voltage follows the DC input voltage in a normal mode, and a value that varies inversely with respect to the DC input voltage, such that the output voltage is substantially constant in another mode.