| 摘要 |
PROBLEM TO BE SOLVED: To control the brightness of an HID lamp in optimum in accordance with the overheating state or deterioration state of the lamp by inputting voltage corresponding to current value of the HID lamp and the lamp voltage of the HID lamp in a microcomputer. SOLUTION: Lamp voltage V1a of an HID lamp 1 is detected with series resistance R1 of the lamp 1, lamp current I1a and voltage V1 corresponding to the resistance value of a thermistor arranged in the vicinity of the lamp 1 are obtained as the output of a voltage-current detecting circuit 12. The voltage V1a and the voltage V1 are inputted in a microcomputer 3, and compared on occasion with a rated value memorized in a memory. Based on the compared result, FET (F1-F4) in a full-bridge circuit arranged in an inverter circuit 8 is controlled through a driver circuit 5, the HID lamp 1 is avoided from an overheating state, and the luminescent efficiency of the HID lamp is controlled in optimum. |
