1. After being interfered by the outside world and carrying some load, the filter parameters have changed and the filtering effect has been significantly reduced.

2. When the resistors at one end and two arms of the transmission are asymmetric, the common mode noise levels caused are inconsistent, and the difference between the two changes into differential mode noise.

3. Some load-bearing loads include those of the switching power supply, which can transmit the Ade switching noise to its input end, which is the output end of the SPWM power inverter power supply.

4. The reason why the noisy sound at the input end is coupled to the output line is that the incoming and outgoing cables are laid in parallel with a small distance. Especially for large-capacity boost types, the input current is relatively large, and the coupling of noisy sound is serious.

5. If the transmitted filter uses a single arm connected in series with an inductor, the choke inductor connected in series with a single arm at its input end makes the resistance of the two arms uneven, and some rectifier load is used to alleviate the impact during closing. current.

6. When the ground wires of the common mode filter circuit at the input and output ends are connected to the same point, a ground loop is formed. The common mode noise at the input end passes through the ground wire of the common mode filter circuit at the output end, coupling the common mode noisy sound to At the output end, even adding a second level of EMI filter does not have very good results.