Conductive Noise Suppression with Cancelling for Miniaturization of EMI Filters in PFC Converter

Abstract

This paper proposes a combination of two methods to reduce the conductive noise in power factor correction (PFC) circuits. The two methods do not involve large additional components.The first method achieves noise cancellation with an additional circuit using general-purpose transistors. It reduces the noise voltage by injecting a current of equal magnitude and opposite polarity to the leakage current generated by the switching device, which is the noise source, according to its operation. This is effective for not only average (AV) values but also quasi-peak (QP) values since the changes in the noise waveform are tracked.The second method applies a control signal with a spread spectrum. The application of the spread spectrum for PFC has conventionally been effective only for AV values. This paper shows the conditions required to be effective for QP values as well.The combination of these methods is confirmed to reduce the conductive noise by about 30 dB in the frequency range below 1 MHz, which is the dominant factor affecting sizing of EMI filters. This is equal to the attenuation achieved by a single LC filter stage.

Limitation of switching frequency to improve characteristics and suppression of input current distortion for critical mode PFC

“…On the other hand, AV values did not show any substantial difference. In the conventional method, frequency strongly fluctuates within input half‐period, and one can assume that AV values were suppressed due to the spread spectrum effect 17 …”

“…In the conventional method, frequency strongly fluctuates within input half-period, and one can assume that AV values were suppressed due to the spread spectrum effect. 17 Now, at input voltage of 115 V, frequency does not exceed 150 kHz even in the conventional method, and frequency limitation makes no difference.…”