Electronic ballasts are used to start and drive lamps, such as fluorescent lamps and high intensity discharge (HID) lamps, in artificial lighting applications. In general, the ballast converts input AC power to an intermediate DC and an output stage inverter generates an AC output to drive the lamp, and the conversion of the input AC to the intermediate DC in certain ballasts involves power factor correction. During normal operation, the ballast operates in closed-loop fashion to regulate the amplitude of the AC signals driving the lamp load. However, when the lamp load is removed from such a ballast, the inverter output voltages (open-circuit voltage) can be as high as the intermediate DC voltage level. In certain situations, such high open-circuit voltage levels may be undesirable, and there remains a need for improved HID ballast designs to provide regulated AC drive currents to HID lamps without excessive open-circuit voltages.
USPTO Backgrounds
USPTO Backgrounds