Common Mode Inductance Principle

Common Mode Inductance Principle

Before introducing the common mode inductance, first introduce the choke coil. The choke coil is a low impedance coil used to attenuate the high frequency current in the circuit. In order to improve its inductance choke coils usually have a core made of soft magnetic material. Common mode choke coils have multiple identical coils in which current flows in opposite directions, so the magnetic fields cancel out in the core of the choke coil. Common mode choke coils are often used to suppress interference radiation, because such interference currents are reversed in different coils, increasing the EMC of the system.
Common-mode signal and differential-mode signal are only a relative quantity. Common-mode signal is also called common-mode noise or ground-to-ground noise, which refers to the noise of the two lines to the ground respectively. For switching power supply (a high-frequency power conversion device, It is a type of power supply. Its function is to convert a voltage of a level into the voltage or current required by the user through different forms of architecture.) For the input filter, the neutral line and the live line are respectively Earth's electrical signal. Although neither the neutral wire nor the live wire is directly connected to the ground, the neutral wire and the live wire can be connected to the ground through parasitic capacitance or stray capacitance or parasitic inductance on the circuit board, respectively. Differential mode signal refers to the direct signal difference between two lines, which can also be called TV difference.

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