| 摘要 |
PROBLEM TO BE SOLVED: To make a current limiting element small and stably light a discharge lamp by connecting the discharge lamp to the second AC voltage source for a set period when the integrated value becomes larger than a prescribed value, and connecting the discharge lamp to the first AC voltage source when the set period expires. SOLUTION: The lamp current is abruptly increased when a switch SW1 is connected to a contact point (a) side, and a comparing circuit CPo outputs a trigger when the output V2 of an integrating circuit 1 exceeds the set value Vrefo. A monostable multivibrator 2 is triggered by Vcpo, the switch SW1 is connected to a contact point (b) side for a set period T by a switch switching circuit 3, and the lamp current is gradually decreased. When the set period expires, the signal Vs of the monostable multivibrator 2 becomes an L-level, the switch SW 1 is connected to the contact point (a) side by the circuit 3, and the lamp current is quickly increased again. The time constant of the integrating circuit 1 is set longer than the AC cycle of the lamp current and shorter than the time constant of the lamp runaway. |
