| 摘要 |
PROBLEM TO BE SOLVED: To mitigate overheat of a lamp filament part by suppressing switching on and off of a fluorescent lamp 32 at the last stage of its life. SOLUTION: Inductance 31 one end of which is connected to the crossing point of a pair of forward series switching elements 11, 12 alternately switching on and off, and a parallel circuit of the fluorescent lamp 32 and a capacitor 33 for preheating are provided. A dc power supply 40 to supply a current to the fluorescent lamp 32 through the first switching element 11 is provided, and an auxiliary capacitor 50 to supply a current to the fluorescent lamp 32 through the second switching element 12 is provided. A first control circuit 70 to determine whether the fluorescent lamp 32 exists or not by detecting a current biased to the filament of the fluorescent lamp 32 from the dc power supply 40 through impedance elements 61, 62, 63, and a second control circuit 80 to operate by detecting the rise of a voltage developed across the fluorescent lamp 32 are provided. A third control circuit 90 to cancel the operation of the first control circuit 70 when the second control circuit 80 operates. COPYRIGHT: (C)2004,JPO |
