Common Mode Choke

- Aug 16, 2018 -

Common mode Choke, also called common-mode Choke, is used to filter common-mode electromagnetic interference signals from a computer's switching power source. In the board card design, the common mode inductor also plays the role of EMI filtering, which is used to suppress the electromagnetic wave radiating outward from the high speed signal line.

The computer's internal motherboard is a mix of high frequency circuits, digital circuits and analog circuits that produce a lot of high frequency electromagnetic waves that interfere with each other when they work, known as EMI. EMI also emits electromagnetic radiation from the mainboard wiring or the external cable, causing electromagnetic radiation pollution and affecting the normal operation of other electronic equipment.
The chip on PC board card is not only an electromagnetic interference object, but also an electromagnetic interference source. In general, we can divide these electromagnetic interference into two types: serial mode interference (differential mode interference) and common mode interference (ground interference). Take two PCB wires (wires connecting the components of the main board) on the main board as an example. The common mode interference is the interference caused by the potential difference between two walking lines and PCB ground wire. The cross mode interference current ACTS between two signal lines and its transmission direction is consistent with the waveform and signal current. The common-mode interference current ACTS between the signal line and ground wire, and the interference current flows through one half of each signal line in the same direction and takes ground wire as the common circuit.

The common-mode inductance is essentially a two-way filter: on the one hand, it is necessary to filter the common-mode electromagnetic interference on the signal line; on the other hand, it is necessary to restrain itself from sending out electromagnetic interference to avoid affecting the normal operation of other electronic equipment in the same electromagnetic environment.