| 摘要 |
PURPOSE:To improve a power factor by preparing a reference sine wave in response to phase difference computed by a phase-difference arithmetic means and a modulation factor computed by a modulation-factor arithmetic means. CONSTITUTION:A power-factor improving circuit has a full-wave rectifier circuit 4, a switching element 9, etc., and a control circuit for the power-factor improving circuit is constituted of an input current detector 11, a supply-voltage waveform detector 12, a CPU 17, and a supply voltage detector 18. The CPU 17 has a modulation-factor arithmetic means 19 as well as a phase-difference arithmetic means 14, etc. The phase-difference arithmetic means 14 computes phase difference phi to AC supply voltage v0 of the switching element 9 based on an input current value i0, and the modulation-factor arithmetic means 19 computes the modulation factor U of the element 9 based on a supply voltage value v0. Consequently, a reference sine wave vk is prepared based on the phase difference phi and the modulation factor H, and the switching element 9 is controlled by a control signal S1 by the reference sine wave. Accordingly, phase difference can be brought to zero, etc.
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