| 摘要 |
PURPOSE:To prevent the early blacking and life deterioration of by cold start of a discharge lamp by suppressing the frequency to a switching frequency in which filament preheating can be performed but discharge lamp start can not be performed for a determined period from power source input. CONSTITUTION:A switch 42 is ON by a filament preheating means 4 until a determined time is elapsed after power source input. Thus, the synthetic capacity of capacitors 16, 41 is relatively small, and the resonance frequency of a series resonance circuit is raised. Therefore, the ON-time of base current is controlled shorter, the oscillating frequency of an inverter 1 is increased, and the output voltage is reduced. At this time, the induced voltage of the secondary winding 11s of an output transformer 11 given between both electrodes of a discharge lamp 2 is set lower than the start voltage of the discharge lamp 2, whereby the discharge lamp 2 can perform the soft start for heating a filament without discharging the discharge lamp 2 by the high frequency output from the inverter 1. |
