
Common mode inductors have plug-ins, patches, and integrated forming. According to the actual circuit selection, plug-ins can only be installed on the patch.
This is the main factor to consider. In general, special attention should be paid to the frequency band required to be filtered in the selection. The specifications of common-mode inductance should be read, mainly the impedance frequency curve. The following figure is a common mode inductance impedance characteristic curve, different frequencies correspond to different impedance values.
Due to common mode inductor processing technology and other problems, the coil winding of common mode inductor cannot be exactly the same, which will lead to magnetic leakage, resulting in the so-called "leakage". It is necessary to consider the impact of differential mode impedance on signals, especially high-speed signals, but sometimes the leakage is not the same, which is bad. The cost of adding differential mode inductors can sometimes be saved by using the leakage inductance produced by common-mode inductors. Therefore, we often use EMI filters like the following, which is the secondary EMI filter.
For example, cost, brand and so on will become important factors in choosing common mode inductors.