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Why common mode inductors can prevent EMI
Sep 17, 2018

Why common mode inductors can prevent EMI

Why is the common mode inductor able to prevent EMI? To figure this out, we need to start with the structure of the common mode inductor.

  The common mode inductor filter circuit, 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 reverse). Thus, when a normal current in the circuit flows through the common mode inductor, the current generates a reverse magnetic field in the in-phase wound inductor and cancels each other. At this time, the normal signal current is mainly affected by the coil resistance (and a small amount of leakage). Damping caused by the sense); when there is a common mode current flowing through the coil, due to the same direction of the common mode current, the same magnetic field is generated in the coil to increase the inductance of the coil, so that the coil exhibits high impedance and produces A strong damping effect is used to attenuate the common mode current for filtering purposes.

In fact, when one end of the filter circuit is connected to the interference source and the other end is connected to the interfered device, La and C1, Lb and C2 form two sets of low-pass filters, which can make the common mode EMI signal on the line be controlled at a low level. On the level. The circuit can suppress the external EMI signal transmission, and can attenuate the EMI signal generated when the line itself works, and can effectively reduce the EMI interference intensity.

A small common mode inductor produced in China adopts high frequency noise suppression countermeasures, common mode choke coil structure, no signal attenuation, small size, convenient use, good balance, convenient use and high quality. Widely used in double-balanced tuning devices, multi-frequency transformers, impedance transformers, balanced and unbalanced conversion transformers, etc.

  There is also a common mode filter inductor/EMI filter inductor with ferrite core, double wire winding, good noise suppression countermeasures, high common mode noise suppression and low differential mode noise signal suppression, low differential mode noise signal suppression interference The source is difficult to be deformed in a high-speed signal, has a small volume, has a good balance, is easy to use, and has high quality. Widely used in suppressing electronic equipment EMI noise, USB lines for personal computers and peripheral devices, DVC, STB IEEE1394 lines, liquid crystal display panels, low-voltage differential signals, etc.

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