| 摘要 |
PROBLEM TO BE SOLVED: To provide a power supply device for high pressure discharge lamp, which can establish lighting with a stable illuminance despite varying supply voltage or supply frequency by sensing the voltage and current to be fed to the discharge lamp, and performing a constant power control. SOLUTION: Through a series capacitor 34 a high pressure mercury lamp 33 is connected with the output side of an electric leak transformer 13, and a voltage sensing circuit 15 and a current sensing circuit 14 are provided for measuring the load voltage and load current of the lamp. The outputs of these sensing circuits 14 and 15 are fed to a control device 16 having a built-in microcomputer to serve for the control of turning on and off a transistor in an inverter circuit 12, and the AC voltage which is PWM modulated is controlled. When the discharge lamp 33 is lighted and a stable condition is established, the lamp voltage V is measured followed by measurement of the current I, and VxI is calculated. the obtained result is compared with a predetermined reference power value P, and if VI<P, a command is given to the inverter circuit 12 so as to heighten the output power to one stage up. In the opposite case, a command to down one stage is given, and it is possible to establish a stable dimming of the lamp. |
