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How the chip common mode inductor works
Sep 20, 2018

How the chip common mode inductor works

Patch common mode inductors are commonly used in computer switching power supplies to filter common mode electromagnetic interference signals. It plays the role of EMI filtering in the design of the board, and is used to suppress the electromagnetic radiation generated by the high-speed signal line from radiating outward.

The filter circuit of the chip common mode inductor is wound by two coils on the same core, and the turns and phases are the same (winding 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, one end of the filter circuit is connected to the interference source, and the other end is connected to the interfered device to form two sets of low-pass filters, so that the common mode EMI signal on the line can be controlled at a very low 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.

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