| 摘要 |
PROBLEM TO BE SOLVED: To prolong the service life of a discharge lamp. SOLUTION: Parallel circuits of resistors R1, R1 and switches SW1, SW2 are connected in series to first and second pre-heating windings n3, n4 and first and second filaments f1, f2 respectively. A counter circuit 4 counts the frequency of standing up of DC current as the frequency N beginning start of a discharge lamp LA, and the switches SW1, SW2 are alternately turned on and off periodically every time the frequency N exceeds a specified value. Thereby, polarizing capability of deflecting a polarity in the starting direction of the discharge lamp LA to one side can be reduced, the sort life caused by on and off of the discharge lamp LA which consumes only the one side filament in the early stage can be prevented, and the life of the discharge lamp LA can be lengthened. |
