Take you to a simple understanding of what is a Common-mode inductor

Release time:

Feb 18,2022

Common-mode inductors are also called common-mode choke coils, which are often used in computer switching power supplies to filter common-mode electromagnetic interference signals. In the design of the board, the Common-mode inductor also plays the role of EMI filtering, which is used to suppress the electromagnetic wave generated by the high-speed signal line and radiate outwards.

customized Common-mode inductor
Common-mode inductor manufacturers tell you that various high-frequency circuits, digital circuits and analog circuits are mixed on the motherboard inside the computer. When they work, they will generate a large number of high-frequency electromagnetic waves that interfere with each other, which is EMI. EMI will also be emitted through the motherboard wiring or external cables, causing electromagnetic radiation pollution and affecting the normal operation of other electronic devices.
The chip on the PC board is not only an electromagnetic interference object, but also an electromagnetic interference source in the working process. In general, we can divide these electromagnetic interferences into two categories: series mode interference (differential mode interference) and common mode interference (ground interference). Common-mode inductor manufacturers tell you that taking the two PCB traces on the main board (the wires connecting the components of the main board) as an example, the so-called series-mode interference refers to the interference between the two traces; while the common-mode interference is the Interference caused by the potential difference between the two traces and the PCB ground. The common-mode inductor manufacturer tells you that the series-mode interference current acts between the two signal lines, and its conduction direction is consistent with the waveform and signal current; the common-mode interference current acts between the signal line and the ground wire, and the interference current flows between the two signal lines Each of the above flows through one-half and in the same direction, and takes the ground wire as the common circuit.
Common-mode inductor manufacturers tell you that if the common-mode current generated by the board is not filtered through attenuation (especially common-mode current on high-speed interface traces such as USB and IEEE 1394 interfaces), then the common-mode interference current can easily pass through Interface data lines generate electromagnetic radiation—common-mode radiation due to common-mode currents in the cable. The US FCC, CISPR22 of the International Radio Interference Special Committee, and my country's GB9254 and other standards and regulations all have relevant restrictions on the common mode conducted interference and radiated emissions of the communication ports of information technology equipment. In order to eliminate the interference signal input on the signal line and various induced interference, we must reasonably arrange the filter circuit to filter the interference of common mode and series mode. Common-mode inductor is an integral part of the filter circuit.
The common-mode inductor is essentially a two-way filter: on the one hand, it needs to filter out the common-mode electromagnetic interference on the signal line, and on the other hand, it needs to suppress the electromagnetic interference from being emitted to the outside, so as to avoid affecting the normal operation of other electronic devices in the same electromagnetic environment. Work.