| 摘要 |
PROBLEM TO BE SOLVED: To securely start a discharge lamp, and to securely protect and control a discharge lamp at the end of lifetime thereof with the simple circuit structure by detecting voltage corresponding to the lamp voltage of each discharge lamp, and controlling the output of a high frequency power source on the basis of the voltage, which is selected by an OR circuit for selecting the maximum voltage among the voltage of the detected voltage. SOLUTION: End voltage of each discharge lamp 3a, 3b, 3c is detected by each voltage detecting circuit 5a, 5b, 5c, and the highest voltage among them is selected by an OR circuit 6. A control circuit 7 receives the highest lamp end voltage from the OR circuit, and restricts the operation of a high frequency power source 1 so that the voltage works as the discharge lamp start voltage. The discharge lamp 3 having the highest voltage starts for lighting, and the voltage of the discharge lamp 3a is lowered by this start of lighting. As a result, the voltage of the discharge lamp 3a does not achieve the maximum value, and the OR circuit 6 performs the control on the basis of the maximum value of the voltage of the discharge lamp 3b or 3c, which is not lighted. |
