PURPOSE:To feed back energy by a spike voltage to a power source side without loss by connecting an absorbing capacitor to switch over the passage of a current between charging time and discharging time. CONSTITUTION:The connection of an absorbing capacitor 6 is switched by switching elements 16, 17. When a spike voltage is charged, the capacitor 6 is connected between the high voltage side terminal of the primary side DC power source and the collector terminal of a main transistor 1, and when discharged from the capacitor 6, the capacitor 6 is connected between the low voltage side terminal of the primary side DC power source and the high voltage side terminal of the primary side DC power source.
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