Investigation and Reduction of a Low-Frequency EMI Noise of AC/DC Power Adapters with Diode Bridge as Input Rectifier

摘要

For AC/DC power adapters with a diode bridge as the input rectifier, when the differential mode EMI filter is placed at DC bus instead of AC line, a low-frequency component can be observed in the measured EMI noise spectrum, and it tends to violate the conducted EMI standard. The mechanism of such a phenomenon is introduced and quantified, the analysis model is built up in the paper. Besides, the methods to reduce the low-frequency noise component are investigated and validated by experiments, such as applying an X-capacitor on AC line or using fast recovery diodes, ultra-fast recovery diodes, and qspeed diodes. Both simulations and experiments verify the analysis.