| 摘要 |
PROBLEM TO BE SOLVED: To provide a lighting device capable of coping with the condition at the time of termination of service life without increase in loss during normal operation. SOLUTION: Both fluorescent lamps FL1, FL2 are started in their operation through a stabilizer 8 at the time of no-power-failure. A main current between filaments FL1a, FL1b flows without passing through positive characteristic thermistors R1, R2 and can reduce its current loss, thereby restraining increase in consuming power and preventing decrease in efficiency. When generation of short-circuit causes an overcurrent to flow at the termination time of the service life of the lamp FL1, increase in temp. occurs and the resistance values of the thermistors R1, R2 is increased sharply to thereby restrain the flow of overcurrent in the filaments FL1a, FL1b, leading to prevention of burning damage in the filament circuit. At the time of power failure, the lamp FL1 is lighted up with the output of an invertor circuit 14. The main current between the filaments FL1a, FL1b after the lighting up flows in the thermistors R1, R2, but the output is small and loss in the current is not large. When an overcurrent flows quick detection is made possible. |
