Filter technology is an effective measure to suppress interference, especially in dealing with switching power supply EMI signal transmission interference and some radiation interference, has obvious effect.
Any power line conduction interference signal, can be used differential mode and common mode interference signal to represent.
Differential mode interference is transmitted between two conductors, belonging to symmetry interference; common mode interference between the wire and the ground (chassis) transmission, are asymmetric interference. Under normal circumstances, the differential mode interference is small, the frequency is low, the interference caused by smaller, common mode interference amplitude, high frequency, but also through the wire to produce radiation, caused by greater interference. Therefore, to weaken the conduction interference, the EMI signal control in the relevant EMC standards below the limit level. In addition to suppressing interference sources, the most effective way is to install the EMI filter in the switching source input and output circuits. The operating frequency of the general equipment is about 10 ~ 50 kHz. EMC limits the limits of the conducted interference levels specified by many standards from 10 kHz. On the switching power supply generated high-frequency EMI signal, as long as the choice of the corresponding decoupling circuit or network structure is relatively simple EMI filter, it is not difficult to meet the EMC standard filtering effect.