| 摘要 |
PURPOSE:To stably start a discharge lamp without a starting equipment by providing a smoothing capacitor and a current detector and lighting the discharge lamp when the voltage on the d.c terminal of the smoothing capacitor becomes highest. CONSTITUTION:A commercial a.c power source 1 is rectified through a rectification circuit 2 so as to generate a d.c voltage including a ripple voltage. The generated d.c voltage is applied to a smoothing capacitor 3 and a series circuit of a current detecting resistance 4 which detects a current iC flowing through the capacitor 3. When the direction of the current iC is reversed, that is, the terminal voltage of the capacitor 3 becomes highest, switching elements SW1 to SW4 are controlled to be opened/closed so as to switch the mode. The elements SW1 to SW4 charges/discharges the capacitor 5 on the preheat mode and preheats filaments 6a, 6b. Next, on the starting voltage generation mode due to the opening/closing control, the voltage twice the voltage 1 is applied to the discharge lamp 6 so that it is possible to obtain the voltage necessary for the stable starting of the discharge lamp. |
