| 摘要 |
PURPOSE:To detect the potential of a half-wave discharge without inducing the generation of high voltage by shunting the current flowing in a DC cutting means provided between an electronic ballast means and a discharge lamp with a resistor. CONSTITUTION:When a discharge lamp 1 is normally lighted, the discharge current is shunted by a capacitor 9 connected in series to the primary side of a current transformer 10 and a damper resistor 8 connected in parallel with it, and the discharge lamp 1 is stably lighted. When a half-wave discharge occurs at the final stage of the life of the discharge lamp 1, the lamp current contains the DC component, electric charges are accumulated in the capacitor 9 serving as a DC cutting means, the voltage across both ends of the capacitor 9 rises, and the potential of the resistor 8 connected in parallel with it rises. The voltage taken out via a capacitor 31 is applied to the emitter of a Tr 40 and the collector of a Zener diode 41. The current flowing in the capacitor 9 is shunted by the damper resistor 8, and the charge voltage of the capacitor 9 does not become high voltage. A closed circuit is formed by the damper resistor 8, and the charge voltage is not applied directly to the discharge lamp 1. |
