| 摘要 |
PROBLEM TO BE SOLVED: To satisfactorily protect a circuit by detecting the light/heavy state of a load by means of detecting the output DC voltage of a partial smoothing power supply circuit. SOLUTION: A rectifier DB, an inverter circuit 11 converting DC voltage into the AC voltage of a high frequency by turning on/off of FETs Q1 and Q2 and applying it to a load LD formed of discharge lights La1 and La2, a partial smoothing power supply circuit 12 for smoothing the vicinity of the trough of output voltage from the rectifier DB and obtaining DC voltage and a control circuit 13 detecting DC voltage changing according to the light/heavy state of the load LD and controlling the invertere circuit 11 according to the detection result are installed. The control circuit 13 changes a steady lighting frequency into a frequency, which is higher than the frequency and becomes not less than the detection threshold of a detection part 131, when a voltage level as a detection result becomes higher than prescribed threshold voltage (reference voltage), for example. |
