Why can common mode inductor prevent EMI? To understand this, we need to start with the structure of the common-mode inductor.
The common mode inductor filter circuit, La and Lb are the common mode inductor coil. The two coils are wound around the same core with the same number of turns and the same phase. In this way, when the normal current in the circuit flows through the common-mode inductor, the current generates the opposite magnetic field in the inductor coil with the same phase winding and cancels with each other. At this time, the normal signal current is mainly affected by the coil resistance (and a small amount of damping caused by leakage inductor). When a common-mode current flows through the coil, due to the homogeneity of the common-mode current, the coaxial magnetic field will be generated in the coil and the inductance of the coil will be increased, so that the coil will show high impedance and have a strong damping effect, so as to attenuate the common-mode current and achieve the purpose of filtering.
There is a kind of common mode filter inductor/EMI filter inductor using ferrite core, and bifilar winding countermeasures of noise suppression, high common mode noise suppression and low differential mode noise suppression, suppress interference sources and low differential mode noise signal is difficult to deformation in the high speed signal, small volume, it has good balance, the advantages of convenient use and high quality. Widely used in restraining EMI noise of electronic equipment, USB circuit of personal computer and peripheral equipment, IEEE1394 circuit of DVC and STB, LCD panel, low voltage differential signal