End of life control for parallel lamp ballast

摘要

A light fixture includes a ballast and a plurality of lamps connected to the ballast in parallel. The ballast provides an output signal to the plurality of lamps as a function of a 1st steady state condition. When the ballast senses an end-of-life condition for a lamp of the plurality of lamps, the ballast increases the frequency of the output signal provided to the plurality of lamps until the lamp ceases to conduct current. When the lamp ceases to conduct current, the ballast decreases the frequency of the output signal to a frequency determined as a function of a 2nd steady state condition different from the 1st steady state condition. A total current of the 2nd steady state condition is proportional to a total current of the 1st steady state condition as a function of the number of lamps exhibiting an end-of-life condition.

主权项

1. A ballast operable to provide an output signal to a plurality of lamps connected to the ballast in parallel, said ballast comprising:
an output circuit operable to provide an output signal to the plurality of lamps connected to an output of the ballast as a function of a control signal; an end-of-life monitor operable to provide a signal indicative of an end-of-life condition of a lamp of the plurality of lamps; a controller operably connected to the output circuit and the end-of-life monitor, said controller functional to:
generate the control signal as a function of a first steady state condition, wherein the control signal determines a frequency of the output signal;sense an end-of-life condition in a lamp of the plurality of lamps as a function of the signal indicative of an end-of-life condition from the end-of-life monitor;in response to sensing the end-of-life condition in the lamp, increase the frequency of the output signal until current ceases to flow through the lamp; andin response to current ceasing to flow through the lamp, providing the control signal as a function of a second steady state condition, wherein the second steady state condition is different from the first steady state condition, and the second steady state condition has a current greater than zero.