| 摘要 |
PURPOSE:To suppress an unstable discharge and an increase of stress to switching devices of an inverter at the start of the on-period by providing the inverter feeding the high-frequency power to a discharge lamp and a means feeding large power and small power in turn to the discharge lamp from the inverter. CONSTITUTION:When a dimming switch 8 is closed, a variable resistor 72 is connected in parallel with the resistor 71 of an oscillating circuit 7 with the high level of the output of a rectangular wave generating circuit 5, the oscillation frequency of the oscillating circuit 7 becomes f2, and it is returned to the original frequency f1 with the low level. When the current amplitude for the frequency f2 is set to about 10% of the current amplitude for the frequency f1, the light quantity by the current of f2 is almost negligible, the current is continuously fed to the discharge lamp 3 during dimming, thus an unstable discharge and an increase of stress to switching devices 21, 22 of an inverter 2 can be suppressed. The unstable discharge and the increase of stress to the switching devices 21, 22 of the inverter 2 at the start of the on-period can be suppressed by modifying the circuit to feed small power during the stop period of the power feed. |
