| 摘要 |
PURPOSE:To enable dimming lighting of a fluorescent lamp easily in low light flux by arranging a constant voltage circuit and a level detecting circuit between a light dimming control controller and an inverter circuit, and fixing the lower limit voltage. CONSTITUTION:A light dimming signal to vary light output is outputted by a light dimming control controller 4, and the light dimming signal charges/ discharges electricity to/from a capacitor C through a light emitting element LED and a light receiving element Q3, and varies voltage V1. The voltage V1 changes linearly to a duty of the light dimming signal. The voltage V1 is inputted to an inverter circuit through resistors R7 and R8, and varies the light output of a fluorescent lamp. A constant voltage circuit 5 makes the lower limit voltage of voltage V3 constant in the vicinity of the lower limit area of a light dimming range so as to give constant brightness out of relation to a duty. A level detecting circuit 6 puts the voltage V3 on a zero level when the voltage V1 becomes specific voltage or less, and puts the inverter circuit in a preheating mode. A change in output light flux becomes more moderate in the lower limit area than the other area by the constant voltage circuit 5 and the detecting circuit 6. |
