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How common mode inductors act as bidirectional filters in circuits
- 2020-07-02-

Talking aboutCommon mode inductanceBefore, we talked about what mutual inductance is. When the current in a coil changes, an induced electromotive force is generated in another coil nearby, which is called mutual inductance. Mutual inductance is a common electromagnetic induction phenomenon that not only occurs between two coils wound on the same iron core, but can also occur between any two circuits that are close to each other. The mutual inductance has a special application, that is, common mode inductance. Industrial-mode inductors can also be called common-mode chokes, which are often used in computer switching power supplies to filter common-mode electromagnetic interference signals. In the board design, the common mode inductor also plays the role of EMI filtering, used to suppress the electromagnetic wave generated by the high-speed signal line to radiate outward.

Common-mode inductors also play the role of a two-way filter in the circuit, so what points do they need in order to be able to act as a two-way filter in the circuit? Here is a brief talk:

Common mode inductors need to have high initial permeability. The initial permeability of common mode inductors is 5-15 times that of ferrite, so it has a large insertion loss. In the suppression of conducted interference, it performs better than ferrite.

Common mode inductors need to have high saturation magnetic induction, 2-3 times higher than ferrite. In the case of strong current interference, it is not easy to magnetize saturation.

Common mode inductanceIt needs to have excellent temperature stability. The higher the Curie temperature, the higher the temperature fluctuation, the alloy property change rate is significantly lower than ferrite, it has good stability, and the property change is close to linear.

Common mode inductors need to have flexible frequency characteristics, and flexibly adjust the process to obtain the required frequency characteristics. Different manufacturing processes and appropriate coil explosions can obtain different impedance characteristics to meet the filtering requirements of different bands, and its impedance value is much higher than that of ferrite.

Currently,Common mode inductanceThe application is very wide. It can be used in radio frequency and wired communication, information technology equipment, radar detectors, automotive electronics, cellular phone, suction machines, audio equipment, PDAs, wired remote control systems, low pressure requirements Electric modules, electronic measuring instruments, computer room equipment, switching power supplies, and measurement and control systems can all be seen!