Definition and role of common mode inductance

Common mode choke coils, also known as common mode choke coils, are often used in computer switching power supplies to filter common mode electromagnetic interference signals. The common mode inductor is essentially a two-way filter: on the one hand, it needs to filter out the common mode electromagnetic interference on the signal line, and on the other hand, it needs to suppress the electromagnetic interference emitted by itself, so as not to affect the normal working electromagnetic environment of other electronic devices in the same area. In short, the production of common mode inductors should meet the following requirements: the wires wound on the coil core should be insulated from each other to ensure that there is no breakdown and short circuit between coil turns under the action of transient overvoltage.

Common mode choke coils, also known as common mode choke coils, are often used in computer switching power supplies to filter common mode electromagnetic interference signals. In the design of the circuit board, the common mode inductor also plays the role of EMI filtering, which is used to suppress the electromagnetic waves radiated by the high-speed signal lines.

The common mode inductor is essentially a bidirectional filter: on the one hand, it needs to filter out the common mode electromagnetic interference on the signal line, and on the other hand, it needs to suppress the electromagnetic interference emitted by itself, so as not to affect the normal working electromagnetic environment of other electronic devices in the same area.

In short, the fabrication of common mode inductors should meet the following requirements:

(1) The wires wound on the coil core should be insulated from each other to ensure that there is no breakdown and short circuit between coil turns under the action of instantaneous overvoltage;
(2) When the coil flows through a large instantaneous current, the magnetic core should not be saturated;

(3) The magnetic core in the coil should be insulated from the coil to prevent breakdown between the two under the action of instantaneous overvoltage;

(4) The coil should be wound in a single layer as much as possible to reduce the parasitic capacitance of the coil and improve the ability of the coil to withstand transient overvoltage.
What are the requirements for a common mode inductor? Generally speaking, pay attention to selecting the desired frequency band, the larger the common mode impedance, the better. Therefore, when choosing a common mode inductor, you need to check the device information, mainly based on the impedance frequency curve. In addition, attention should be paid to the effect of differential mode impedance on the signal, especially for high-speed ports.