An illustrative converter embodiment employs an oscillator comprising a capacitor and a comparator. The capacitor is alternately coupled to a charging current source and a discharging current source, the charging current source operating to charge the capacitor at a first rate and the discharging source operating to discharge the capacitor at a second rate. The comparator asserts an output signal when the capacitor charges to a first threshold voltage and deasserts the output signal when the capacitor discharges to a second threshold voltage. The first rate may be proportional to the input voltage and the second rate may be fixed. The output signal may be applied to the gate of a transistor to alternately apply the input voltage across an inductor and to apply current from the inductor to a capacitance. The duty cycle of the output signal is inversely proportional to the input voltage, or at least approximately so.