Common mode inductance is often used to filter common mode electromagnetic interference signals in the switching power supply of the computer.
Release time:
2024-08-22
Common mode inductor filter circuit, La and Lb is the common mode inductor coil. The two coils are wound on the same core with the same number of turns and phase (reversed winding). In this way, when the normal current in the circuit flows through the common mode inductor, the current generates reverse magnetic fields in the inductor coil wound in 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 current flowing through the coil, due to the same direction of the common mode current, the magnetic field in the same direction will be generated in the coil and the inductive reactance of the coil will increase, so that the coil performance of high impedance, resulting in a strong damping effect, in order to attenuate the common mode current, to achieve the purpose of filtering.
Common mode inductor filter circuit, La and Lb is the common mode inductor coil. The two coils are wound on the same core with the same number of turns and phase (reversed winding). In this way, when the normal current in the circuit flows through the common mode inductor, the current generates reverse magnetic fields in the inductor coil wound in 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 current flowing through the coil, due to the same direction of the common mode current, the magnetic field in the same direction will be generated in the coil and the inductive reactance of the coil will increase, so that the coil performance of high impedance, resulting in a strong damping effect, in order to attenuate the common mode current, to achieve the purpose of filtering.
A variety of high-frequency circuits, digital circuits and analog circuits are mixed on the motherboard inside the computer. When they work, a large number of high-frequency electromagnetic waves interfere with each other, which is EMI. EMI will also be emitted through the motherboard wiring or external cables, causing electromagnetic radiation pollution, affecting the normal operation of other electronic equipment.
The chip on the PC board is not only an electromagnetic interference object, but also a source of electromagnetic interference. In general, we can divide these electromagnetic interferences into two categories: series mode interference (differential mode interference) and common mode interference (ground interference). Taking the two PCB traces on the motherboard (the wires connecting the components of the motherboard) 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 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 line, and the interference current flows through the 1/2 and in the same direction on the two signal lines, and the ground line is the common circuit.
If the common mode current generated by the board is not attenuated and filtered (especially the common mode current on high-speed interface traces such as USB and IEEE 1394 interfaces), the common mode interference current can easily generate electromagnetic radiation through the interface data line-common mode radiation generated by common mode current in the cable. The United States FCC, the CISPR22 of the International Radio Interference Special Committee and my country's GB9254 and other standards and specifications have related restrictions on the common mode conducted interference and radiated emission of the communication port of information technology equipment. In order to eliminate the interference signal input on the signal line and the induction of various interference, we must reasonably arrange the filter circuit to filter the common mode and the series mode interference, the 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 should filter out the common mode electromagnetic interference on the signal line, on the other hand, it should suppress itself from emitting electromagnetic interference, so as to avoid affecting the normal operation of other electronic equipment in the same electromagnetic environment.
Tag:
Share
Contact Us
Service Hotline:
WeChat/TEL：+ 86 18676028669 Warren
Email: warren.wang@yuhongkeji.net
Mobile:+86 19981801317 Toni
WeChat：18161161782
Email: Toni.Tang@yuhongkeji.net
Address: No. 288 Xinping Road, Chaoyang Street, Yuechi County, Guang'an City, Sichuan Province
Focus on us
WeChat Public Number