In the design of common mode inductors should pay attention to several points: common mode wire and wire are mutually insulated; When instantaneous large current passes through the magnetic core, the magnetic core cannot be saturated. In order to prevent the breakdown between the magnetic core and the coil under the action of transient overvoltage, the magnetic core should be insulated from the coil; In order to reduce the parasitic capacitance of the coil, the common mode coil should be wound in a single layer as much as possible to enhance the ability of the coil to withstand transient overvoltage.

The larger the impedance of the common mode inductor, the better, the frequency band of the filter needs to be paid attention to when selecting, so we should select the common mode according to the impedance frequency curve. In addition, pay attention to the differential mode impedance, which will have a certain impact on the signal, especially the port of the high-speed signal.