| 摘要 |
PROBLEM TO BE SOLVED: To reduce a switching frequency of a DC power circuit at the voltage drop, and quickly supply energy to the lamp side by controlling a frequency of a saw-toothed wave according to source voltages before and after lighting through a frequency changing circuit of a saw-toothed wave forming circuit. SOLUTION: An electric current supplied to the primary side of a flyback transformer of a DC power circuit from a DC power source is switched by a MOS transistor, and is supplied to a lamp through an inverter circuit by rectifying secondary side output. In the discharge lamp device, a switching frequency of the MOS transistor 31 is controlled by a PWM control circuit composed of a saw-toothed wave forming circuit 163 containing a frequency changing circuit 185. Source voltages before lighting and after lighting are respectively detected by circuits 185a and 185b of the frequency changing circuit 185, and a circuit having a capacitor 177 and NPN transistors 183a and 183b is controlled according to its voltages. Therefore, the switching frequency is reduced at a low voltage, and high voltage can be supplied to the lamp. |
