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.