| 摘要 |
PURPOSE:To prevent an excessive current at no-load by setting a voltage in such a manner that the output voltage of a comparator is continued to a pulse width modulating part through an OR circuit until the DC voltage on output side becomes lower than a specified maximum voltage at lighting start. CONSTITUTION:At a no-load time when no discharge lamp is connected, or before discharge starts, the DC voltage generated in a DC-AC converter 3, a transformer 4, and a rectifier 5 is higher than a specified voltage. This is detected by the voltage detecting circuit 11a of an open voltage control device 11, and when it is judged higher than a set voltage by a comparator 11b, a control signal is applied to a pulse width modulating part 9b constituting a control circuit 9 through an OR circuit 11c. The pulse width of the control voltage signal to be applied to each FET constituting the converter 3 is controlled narrow by the circuit 9. Thus, the DC voltage on the output side of the rectifier 5 is lowered, and the current carried to each FET at the time of starting the discharge of a discharge lamp is set only within the narrow pulse width, and never become an excessive current. |
