| 摘要 |
PURPOSE:To suppress higher harmonic wave trouble by detecting the input current into a full bridge circuit being boosted with a step-up circuit, and controlling one hand of the pairs of the switching semiconductor elements of the full bridge circuit with low frequency and the other hand with high frequency through a control circuit. CONSTITUTION:The DC power from a rectifying circuit 11 is boosted with a step-up chopper circuit 12, and also the input current is made into sine waves, and high frequency is removed, and it is supplied to a full bridge circuit 13 which supplies a discharge lamp 15 with AC. The average value of the input current to this circuit 13 is detected with a current detecting circuit 16, and on the detection result, a control circuit 17 produces signals to drive each of one pair each of switching semiconductor elements Q2 and Q3, Q4 and Q4 of the circuit 13 with low frequency and high frequency, and the low frequency voltage modulated into high frequency is supplied to a discharge lamp with roughly constant voltage. By the removal of this higher harmonics, the high frequency obstacle is suppressed, and the occurrence of flicker is prevented with the high-speed response by high-frequency-modulated low voltage, and the brightness becomes uniform by constant power. |
