Common Mode Operating Principle

- Sep 06, 2018 -

Differential mode inductors are characterized by their use in high-current situations. As a coil wound around a core increases the current 

flowing into the coil and the core becomes saturated, the most widely used core material on the market is the metal powder core. Especially iron powder materials (due to the low price).

The filter circuit of common mode inductance, La and Lb are common mode inductors. The two coils are wound on the same core, with the same number of turns and phase (wound in reverse). Thus, when the normal current in the circuit flows through the common mode inductance, the 

current produces a reverse magnetic field in the inductor coil wound with the same phase and cancels 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 inductance). When there is a common mode

When the flow flows through the coil, coaxial current will generate codirectional magnetic field in the coil and increase the inductance of the coil. As a result, the coil presents high impedance and produces strong damping effect, so as to attenuate the common mode current and achieve the purpose of filtering.In fact, by connecting one end of the filter circuit to the interference source and the other end to the interference device, La and C1, Lb and C2 constitute two sets of low-pass filters, which can control the common mode EMI signal on the circuit at a very low level. The circuit can not only suppress the EMI signal from the external environment, but also attenuate the EMIsignalgenerated by the circuit itself, which can effectively reduce the EMI interference intensity.

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 EMI noise suppression of electronic equipment, USB circuit of PC and peripheral 

equipment, DVC, IEEE1394 circuit of STB, LCD panel, low voltage differential signal... And so on.