| 摘要 |
A diode bridge (B1) that performs full-wave rectification on an AC input power supply (Vac) is provided. A switching element (Q1) that performs switching on an output voltage thereof, an inductor (L1) that passes a current interrupted by the switching element (Q1) and that accumulates and emits excitation energy, a diode (D1), and a smoothing capacitor (C1) constitute a step-up chopper circuit. A digital signal processing circuit (13) detects a phase of an input voltage (Vi), and a switching frequency of the switching element (Q1) is modulated in accordance with the phase. Accordingly, the switching frequency can be appropriately modulated without depending on an input voltage, so that a wide range of input voltages can be accepted while suppressing EMI noise with a peak generated in the switching frequency and higher-order frequency components thereof. |
