| 摘要 |
PURPOSE: To maintain constant power to a discharge lamp by adjusting the time of a first driving part of an operating cycle according to an error signal, and adjusting the output power of a power supply continuously toward set-point power. CONSTITUTION: A sensing resistance RS1 is provided on the input side of a switch 40, and a power control circuit 42 receives via a line 44 a first signal which is proportional to the average of momentary currents flowing in the switch 40. By adjusting the set point P of the power control circuit 42, the first signal is added to a second signal having a value proportional to the power at the set point SP, producing an error signal having a value showing the difference between the first and second signals. By changing the switching frequency of the power supply according to the value of the error signal, the length of a first driving part in an operating cycle is adjusted, and the output power of the power supply is adjusted continuously toward the power at the set point SP. Therefore, the power supplied to a discharge lamp 10 is held constant. |
