| 摘要 |
PURPOSE:To suppress the generation of a buzzing sound by an inductance element and prevent a chopper circuit from operating abnormally by adding a dummy load circuit which operates in the half period of a switching circuit to supply a dummy current the inductance elements. CONSTITUTION:The dummy load circuit 8 does not operate except when the switching circuit 4 is in the half period, and a switching element Q2 operates only when it is in a cutoff state in the half period to supply the dummy current ID. Then a coil current IA1 flows without intermittence even during the halt period DT of the switching circuit 4 and the coil current IA1 flows continuously during circuit operation. Consequently, a choke coil L is prevented from generating the buzzing noise. Further, the coil current IA1 is never break, so a rise in the output voltage of the chopper circuit 2 can be suppressed and the output voltage at an output point 2a does not rise when a discharging lamp 6 illuminates, so that a control part 5 can be prevented from malfunctioning. |
