Patent ID: 7274112

Claim:
An uninterruptible power supply for providing power to a load, the uninterruptible power supply comprising: an input to receive input power; an output to provide output power; an input power circuit coupled to the input and having a DC output that provides DC power having a first DC voltage level; a capacitor having a first end coupled to the DC output of the input power circuit and having a second end; a back-up power source coupled to the input power circuit; an output power circuit coupled to the DC output of the input power circuit and to the output of the uninterruptible power supply to provide the output power; and a capacitor discharge circuit coupled to the first end of the capacitor and the second end of the capacitor and configured in a first mode of operation to discharge a voltage across the capacitor, such that an average discharge current through the discharge circuit is inversely proportional to a voltage across the capacitor for a first range of voltages across the capacitor; wherein the capacitor discharge circuit is configured in a second mode of operation such that the discharge current through the discharge circuit is proportional to the voltage across the capacitor for a second range of voltages that is less than the first range of voltages.