The generator has a voltage divider with a number of dividing elements serially connected to each other between two power sources of different voltage levels from each other, and dividing levels from each other, and dividing a potential difference between the two power sources into a plurality of levels of voltage. A switch has a number of switch devices serially connected to each other between the two power sources. The switch devices on the side of one of the two power sources are connected to the output terminal. Trigger turns on the switch devices sequentially from that on the side of the output terminal. Reverse flow preventive circuit prohibits a current flowing through that of the switch devices which is currently turned on from flowing through the voltage dividing elements corresp. to the switch devices which have been already turned on.
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