| 摘要 |
PURPOSE:To detect the lighting state of a discharge lamp and the terminal stage of its life with a simple circuit structure by detecting the normal lighting state of the discharge lamp and the terminal stage state of its life with a comparing circuit having hysteresis characteristic. CONSTITUTION:The input DC power is converted into high-frequency AC by an inverter circuit 4 to light a discharge lamp 11. The lamp voltage is increased at the terminal stage of the life of the discharge lamp 11. The lamp voltage is detected by a lamp voltage circuit 15 and inputted to a comparing circuit 26. The circuit 26 compares the lamp voltage and the reference voltage Vr and judges the normal lighting state of the discharge lamp 11 and the terminal stage state of its life. When the discharge lamp 11 is judged to be in the terminal stage state, the control signal for activating a safety circuit 30 is outputted, and the lighting output from the circuit 4 is decreased via a drive circuit 7. |
