| 摘要 |
PURPOSE:To prevent an unstable discharge and an increase of stress to switching devices of an inverter at the start of the on-period by providing a duty ratio control means and a means controlling the feed power from the inverter when a discharge lamp is lighted. CONSTITUTION:When a dimming switch 8 is turned on, the action of a drive circuit 6 is stopped. The resistance value determining the output frequency of an oscillation control circuit 74 is reduced, the output frequency of an oscillating circuit 7 rises, the impedance of a coil 25 is increased, and the current of a discharge lamp 3 is decreased. The duty ratio for the preset dimming level can be increased, and the stop period of the power feed can be shortened. An unstable discharge and an increase of stress to switching devices 21, 22 of the inverter 2 at the start of the on-period for dimming by duty ratio control can be suppressed. |
