| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of an arc cut of a discharge lamp. SOLUTION: A MOSFET 5 is connected in series to primary winding 41 of an output transformer 4, and an anode of a diode 6 is connected to a connecting point of the primary winding 41 and the MOSFET 5, and a cathode is connected to a smoothing capacitor 7. Voltage is impressed on a discharge lamp 10 through an inverter 11 from the capacitor 7. Output voltage of the discharge lamp 10 is detected by resistors 22, 23 and 24, and an electric current of the discharge lamp 10 is detected by a resistor 20 connected in series to the resistor 24. A shunt regulator 56 to be turned on when voltage of the resitors 20 and 24 is larger than first reference voltage, a photodiode 51 whose light emitting condition changes according to this ON and a phototransistor 52 are provided, and a driving device 62 controls ON and OFF of the MOSFET 5 according to output voltage of the phototransistor 52 and second reference voltage of an oscillating circuit 61. A Zener diode 25 is arranged in parallel with the resistors 23 and 24. |
