Patent ID: 8384310

Claim:
A dimming ballast for operating at least one fluorescent lamp, the ballast comprising: an input rectifier operative to receive an AC input and to produce an initial DC output; a DC-DC converter operatively coupled to the input rectifier to receive the initial DC output and to provide a second DC output; an inverter operatively coupled to DC-DC converter to convert the second DC output to produce an AC output to power at least one fluorescent lamp; an inverter control system operative to provide at least one inverter control signal or value to the inverter to control the AC output, the inverter control system receiving an end-of-life signal and a dimming signal or value indicating a desired dimming level for the AC output, the inverter control system operative in a first mode when the end-of-life signal is in a first state to provide the at least one inverter control signal or value based at least partially on the dimming signal or value and operative in a second mode when the end-of-life signal is in a second state to provide the at least one inverter control signal or value to control the output at a predetermined low level to prevent damage to a fluorescent lamp in an end-of-life condition; and an end-of-life detection circuit operative to selectively provide the end-of-life signal in the first state when a DC voltage or current of the at least one lamp is in a predefined range, to provide the end-of-life signal in the first state when an AC current of the at least one lamp is less than a predefined AC current threshold value, and to provide the end-of-life signal in the second state when the DC voltage or current of the at least one lamp is outside the predefined range and the AC current of the at least one lamp is greater than the predefined AC current threshold value.