| 摘要 |
PROBLEM TO BE SOLVED: To prevent an overvoltage of a capacitor with a simple and cost-effective structure even if a zero-cross point of an input voltage is displaced in a power supply circuit which performs PAM controls with switching elements short-circuiting the output electric power of a rectifier circuit. SOLUTION: The power supply circuit includes a bridge circuit (12) of diodes (D1-D4) for rectifying AC power, a smoothing circuit (13), which has two capacitors (C1, C2) connected to each other in series and is connected to the output side of the bridge circuit (12), and a PAM control section (15) for switching the switching element (S) at a predetermined timing. The PAM control section (15) includes a zero-cross detection section (15a), which detects that an input voltage of the rectifier circuit (12) is increased more than a predetermined value toward the zero cross point, and a PAM waveform output section (15b), which, when the detection above is carried out by the zero-cross detection section (15a), outputs an ON pulse to the switching element (S). COPYRIGHT: (C)2010,JPO&INPIT
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