PURPOSE:To obtain a normal AC output by generating a series of pulses in synchronization with the control pulses which control the DC input voltage to an inverter wherein thyristors as emloyed, and employing said pulses for firing control. CONSTITUTION:The DC voltage from a DC power supply 3 is supplied to the inverter 2, wherein thyristors are employed, via a DC voltage control circuit 4, which is PWM controlled by a driving circuit 6. In a trigger circuit 5 which controls the operation of the inverter 2; are provided a pulse generator 5a which controls the firing of the thyristors of the inverter 2, and a sequencing circuit 5b which determines the time sequence by which said pulses are supplied to a plurality of the thyristors. A series of high frequency pulses is supplied from a pulse generating circuit 7. The outputs from the circuits 5b and 7 are supplied to a one-shot circuit 5c and an NAND circuit 5d. The outputs therefrom are supplied to an NAND circuit 5e, and the output therefrom controls the firing of the inverter 2.
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