| 摘要 |
PROBLEM TO BE SOLVED: To provide a power unit which can suppress the rise of the output voltage of a smoothing circuit when the load is light and, at the same time, can improve input distortion. SOLUTION: A power unit is constituted of a full-wave rectifier DB1, a high-frequency reverse-current suppressing circuit Do, a smoothing circuit H which obtains a DC power output by smoothing AC power supply Vs, an inverter circuit INVo which converts the DC power output of the circuit H into high-frequency AC power and supplies the AC power to a discharge lamp La, and a high-frequency feedback section FB which is composed of an impedance element Zo, feeds back part of the AC power, and alternately repeats a state where the section FB suck an electric current from the AC power supply Vs and another state where the section FB discharges the smoothing circuit H in accordance with the polarity of the fed back high-frequency AC power. When the load is light, the power unit adjusts the quantity of the electric current flowing to the impedance element Zo by intermittently oscillating the inverter circuit INVo so as to suppress the value of the both-terminal voltage Vdc of the circuit H within a specific range. |
