| 摘要 |
PURPOSE:To precisely detect a half-wave discharging state irrespective of a polarity generated at the time of half-wave discharge without using an expensive transformer by judging an end voltage of a discharge lamp after voltage doubler rectifying. CONSTITUTION:A voltage amplitude value of a lighting discharge lamp 6 is input into a voltage doubler rectifying circuit comprising capacitors 8, 11 and diodes 9, 10. A voltage in proportion to the amplitude value is generated in the capacitor 11. When oxide of an electrode A of the discharge lamp 6 is exhausted so that an electrode B side becomes positive, a discharge current flowing from the electrode B to the electrode A is stopped. With this half-wave discharge, a high voltage capable of making the electrode B positive is applied to the capacitor 8 through the diode 9. Accordingly, since a voltage of the capacitor 11 at the time of half-wave lighting becomes higher than that at the time of normal lighting, the half-wave lighting can be detected. A control circuit 12 can detect the half-wave lighting, to instantly stop operation of an inverter 4. |
