| 摘要 |
PROBLEM TO BE SOLVED: To provide a voltage-control unit having no occurrence of a distortion even in the neighborhood of a zero-cross point of an output voltage and no fluctuation of a voltage waveform even if power fails. SOLUTION: A switching signal of a chopper circuit 4 that controls an applied voltage applied to a primary winding 2 of a transformer 1 is generated by combining a PWM signal generated at a control unit 11 and a synchronized signal generated at a synchronized-signal generating circuit 12. The synchronized signal is the one that repeats 'H' and 'L' at every half cycle of an input- voltage waveform, and always indicates 'L' in the neighborhood of 400μs of the zero-cross point of the input voltage. The chopper circuit 4 is chopping- controlled by the PWM signal only when the synchronized signal indicates 'L'.
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