High Power Common Mode Inductors

High Power Common Mode Inductors

The motherboard inside the computer is mixed with a variety of high-frequency circuits, digital circuits and analog circuits. When they work, a large number of high-frequency electromagnetic waves interfere with each other, which is EMI. EMI can also be emitted out through the wiring of the mainboard or external cables, causing electromagnetic radiation pollution and affecting the normal operation of other electronic equipment.

The chip on the PC board is both an EMI object and an EMI source. Generally speaking, we can divide these EMI into two categories: cascade mode (differential mode) and common mode (ground). Take the two PCB wiring on the motherboard (connecting the main board components of the conductor) as an example, the so-called crosstalk interference, refers to the interference between the two wiring; The common-mode interference is caused by the potential difference between the two lines and the PCB ground wire. The crosstalk mode interference current acts between 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. The interference current flows through half of the two signal lines in the same direction, and the ground wire is the common loop.

If the common-mode current generated by the board is not filtered by attenuation (especially the common-mode current in the wiring of high-speed interfaces such as USB and IEEE 1394), then the common-mode interference current can easily generate electromagnetic radiation through the interface data lines -- the common-mode radiation generated by the common-mode current in the cable. FCC of the United States, CISPR22 of the International Special Committee on Radio Interference and GB9254 of China and other standards and specifications have relevant restrictions on the common mode conducted interference and radiation emission of information technology equipment communication ports. In order to eliminate the input interference signal and the interference induced by the signal line, we must reasonably arrange the filter circuit to filter the interference of common mode and series mode. The common mode inductor is one of the components of the filter circuit.