Patent ID: 7486029

Claim:
A circuit for detecting the end of life of a fluorescent lamp, the circuit comprising: a rectifier for rectifying a voltage signal received from a ballast and outputting a rectified voltage; a phase detector for detecting a phase of the voltage signal and outputting a phase detection signal; a signal separator for separating the rectified voltage, received from the rectifier, on a phase basis to generate a first voltage signal and a second voltage signal in response to the phase detection signal; a first maximum level detector for detecting a maximum level of the first voltage signal; a second maximum level detector for detecting a maximum level of the second voltage signal; a first comparison unit for comparing the first maximum level detected by the first maximum level detector and the second maximum level detected by the second maximum level detector and detecting whether a difference between the first and second maximum levels is higher than a predetermined allowable level; and a controller for determining whether the fluorescent lamp is at the end of life in response to the detection result from the first comparison unit.