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Abstract

A circuit and method for improving EMI noise performance in a bridgeless PFC boost converter. Such a converter comprises a boost inductor having a first end connected to a first AC input terminal and a second end connected to a first junction defined between the anode of a first diode and a first terminal of a first switch; a second terminal of the first switch connected to a common line; a parallel circuit of a capacitance and a load connected between the cathode of the first diode and the common line; a series circuit of a second diode and a second switch connected between the cathode of the first diode and the common line; and a second AC input terminal connected to a second junction defined between the anode of the second diode and the second switch. High-frequency EMI noise is bypassed by placing a first filter capacitor between the first AC terminal and the common line. A second boost inductor may be connected between the second AC input terminal and the second junction, and a second filter capacitor may be connected between the second AC terminal and the common line. The first and/or second filter capacitor has a lower impedance in a high frequency range than the corresponding first or second boost inductor. Preferably the first and second capacitors have substantially the same capacitance.

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