| 摘要 |
PROBLEM TO BE SOLVED: To suppress an abnormal rise in voltage at each end of a smoothing capacitor due to load fluctuations. SOLUTION: An ac power supply PS is rectified by a rectifier DB and smoothed by a smoothing capacitor CB. An inverter 2 supplies a high-frequency voltage to a discharge lamp La while using the smoothing capacitor CB as a power supply. A part of the high-frequency output of the inverter 2 becomes a fed back power supply, and the output of the fed back power supply is fed back to the input side of the inverter via a power factor improving circuit 1. A switching control circuit CN controls the inverter 2 according to whether the discharge lamp La is in a preheated, starting, or on state, thus increasing or decreasing the amount of feedback from the fed back power supply so as to suppress rises in voltage at each end of the smoothing capacitor CB. Thus while a part of the high-frequency output of the inverter 2 is voltage fed back to obtain a high input power factor, rises in voltage at each end of the smoothing capacitor CB can be suppressed by reducing the voltage of the fed back power supply during light load. |
