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The role of common mode inductance in the circuit
Sep 19, 2018

The role of common mode inductance in the circuit

In the circuit, since the problem faced by EMC is mostly common mode interference, common mode inductor is also one of the commonly used powerful components! When the device signal is disturbed, we need to use the common mode inductor to filter the interference signal. why? Here is a brief introduction to the principle and use of common mode inductors.

The common mode inductor is a common mode interference suppression device with ferrite as the core. It is symmetrically wound on the same ferrite toroidal core by two coils of the same size and the same number of turns to form a four-terminal. The device has a suppressing effect on the large inductance of the common mode signal, and has little effect on the differential inductance of the differential mode signal. The principle is that the magnetic fluxes in the magnetic ring are superimposed on each other when the common mode current flows, so that the inductance is relatively large, and the common mode current is suppressed. When the two coils flow through the differential mode current, the magnetic in the magnetic ring By canceling each other, there is almost no inductance, so the differential mode current can pass without attenuation. Therefore, the common mode inductor can effectively suppress the common mode interference signal in the balanced line, and has no effect on the differential mode signal that the line normally transmits.

Under normal circumstances, at the same time pay attention to select the frequency band required for filtering, the larger the common mode impedance, the better. Therefore, we need to look at the device data when selecting the common mode inductor, mainly based on the impedance frequency curve. In addition, pay attention to the influence of differential mode impedance on the signal, mainly focusing on differential mode impedance, paying special attention to high-speed ports.

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