| 摘要 |
PURPOSE:To eliminate noise interference due to a high frequency and make the electrode consumption uniform by using a DC voltage changing the polarity at intervals of a certain time as the voltage applied to a discharge tube. CONSTITUTION:An AC lighting circuit 1 generates a determined AC voltage for discharge tubes 6a and 6b, and a high voltage DC lighting circuit 2 outputs a high DC voltage at the application time and outputs a DC voltage for keeping discharge tubes lighting thereafter. Though the output of the AC lighting circuit 1 is first applied to discharging tubes 6a and 6b through a DC/AC switching circuit 4, the output of the high voltage DC lighting circuit 2 is applied to discharging tubes 6a and 6b when a certain time required for preheating electrodes of discharging tubes elapses. Each time a prescribed time elapses and a supply stop signal D is inputted thereafter, a polarity switching signal 5a is sent from a polarity switching control circuit 5 to a polarity switching circuit 3.
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