| 摘要 |
PROBLEM TO BE SOLVED: To improve the starting characteristic of a high-intensity discharge lamp (HID lamp) to be the load for a power supply unit by eliminating or shortening some periods in the term of its switching elements operating due to voltage regulation, when it is unloaded which causes its load voltage to be lowered. SOLUTION: In the unloaded state of a power supply unit, a timer circuit 4, outputs high-level timer signals during a fixed period in response to the build-up and falling of the output signal of a polarity sensor 1. Transferring the timer signals to a since generator 5, it is so operated during the input period of the high-level timer signals to it as to eliminate a period d2. When performing such an operation is performed, signed the charge stored in a capacitor is not discharged, the voltage across both the terminals of the capacitor is made nearly equal to the voltage of both the terminals of a smoothing capacitor, when repeating such operation several times. As a result, the load voltage of the power supply unit can be increased during a predetermined term without increasing the voltage of the capacitor, and a starting high pulse voltage is applied to a HID lamp within this predetermined period to make improvable its starting characteristic. |
