PURPOSE:To prevent the generation of reverse corona phenomena by providing a stable supplying means for DC voltage controlled of three-phase AC and a means of supplying high voltage intermittently to electric discharge electrodes that supply ions to space by corona discharging. CONSTITUTION:Three phase AC voltage is applied to a three phase thyristor unit 7 via an electromagnetic contactor 8. This three-phase AC voltage is outputted as stable voltage by the unit 7. This unit 7 is controlled by the gate signal supplied to the gate of each thyristor. When this gate signal is applied, an ion signal A is outputted from an automatic thyristor operation unit 10, and when an intermittent signal B is outputted from an intermittent electric charge signal driving unit 11, the signal C is applied via a current limiting reactor 6 to the primary side coil of a votage transformer 5.
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