How Common Mode Inductors Work


A common mode inductor is a common mode effect suppression device with a ferrite core as the core. It is composed of 2 coils with the same ratio and the same number of coil turns, symmetrically wound on the same ferrite core to form a four-terminal device. It exhibits a suppressive effect on large inductors for common-mode signals, while showing little leakage inductance for differential-mode signals is essentially harmless. Its function is that when the common-mode current flows, the magnetic flux in the magnetic ring overlaps each other, so it has a very large inductor, which has a restraining effect on the common-mode current. When the two coils pass through the differential mode current, the magnetic flux in the magnetic ring cancels each other, and there is basically no inductor, so the differential mode current can pass without loss. Therefore, the common-mode inductor can effectively suppress the common-mode electromagnetic interference in the balanced line, and at the same time has no effect on the normal transmission of the differential-mode data signal on the line.


How does a common mode inductor work? 1. Common mode inductors must meet the following requirements: 1) The transmission lines coiled in the core of the coil should be insulated from each other to ensure that the coil is locked to avoid penetration and short-circuit faults under the action of instantaneous overvoltage. 2) When the coil passes through the instantaneous high current, the magnetic core cannot be filled. 3) The magnetic core in the coil is insulated from the coil to avoid penetration between the two under the action of instantaneous overvoltage. 4) The coil should be wound on one side as much as possible, which can reduce the distributed capacitance of the coil and improve the ability of the coil to solve transient overvoltage.

Everyone knows that the advantages of common mode inductors are: 1. The winding is flat, the function is stable, and the high frequency is excellent. The transmission margin above 200kHz is twice that of ordinary magnetic rings. The magnetic ring is 5dB, and the common mode inductance of the flat line is 11db. 2: The horizontal area of the flat transmission line is large. According to the large current, the current density of the enterprise is 1.5 times that of the round copper core wire. The copper loss of the flat transmission line is low, the resistor is small, and the temperature rise is low. The frequency range of the common mode noise generated by the switching power supply circuit is 10kHz~50MHz or even more. In order to efficiently dissipate or suppress this noise, it is specified that the common mode inductor has a higher reactor in this frequency range. How does the common mode inductor suppress the impact noise? First of all, the two sets of coils of the common mode inductor are wound on the magnetic ring with the same number of coil turns and the same orientation, but one set of coils is wound on the left and the other set is wound on the right. Common-mode inductors use high-permeability Mn-Zn ferrite cores or amorphous materials to change the function of common-mode inductors.

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