| 摘要 |
PROBLEM TO BE SOLVED: To provide a power unit which can make the low frequency ripple of output voltage at light load pushed by a relatively simple control means without using a complicated expensive control means. SOLUTION: A control circuit 1 controls on duty of a switching element Q2 arranged within a loop for charging a smoothing capacitor C3 at preheating to be smaller than that of a switching element Q1 in an unbalanced, manner, and makes the waveform of the voltage Vc5 of a capacitor C5 into a trough- stopping voltage waveform, where the difference between the vicinity of the peak of the voltage of an AC power source E and the peak value of the smoothing voltage near the zero cross is made large. Although the waveform of the output voltage at this time becomes one having peaks near the zero cross of the AC power source E and near the peak, since the several peak values are roughly equal, and low frequency ripple is relatively small, it becomes a voltage waveform which is suppressed to a peak voltage which is insufficient for start of a discharge lamp La1. |
