Common mode Choke, also known as common mode choke, is a closed magnetic ring, in which coils with opposite directions and the same number of turns are wound symmetrically. The ideal common-mode choke can suppress the common-mode interference between L (or N) and E, but has no inductive suppression effect on the differential-mode interference between L and N.. However, the incomplete symmetry of actual coil winding will lead to the generation of differential mode leakage inductance. When the signal current or the power supply current flows in the two windings, the directions are opposite, and the generated magnetic fluxes cancel each other, so that the choke coil presents a low impedance. Common-mode noise current (including disturbance current caused by ground loop, also called longitudinal current) flows through the two windings in the same direction, and the generated magnetic fluxes are added in the same direction, so the choke presents high impedance, thus playing a role in suppressing common-mode noise.
Common mode choke is essentially a bidirectional filter: on the one hand, it should filter out the common-mode electromagnetic interference on the signal line, on the other hand, it should restrain itself from emitting electromagnetic interference to avoid affecting the normal work of other electronic equipment in the same electromagnetic environment. �% 82
Common-mode choke can transmit differential-mode signals, DC and low-frequency differential-mode signals can pass through, but it presents great impedance to high-frequency common-mode noise, so it can be used to suppress common-mode current disturbance.
Application of common mode choke in Switching Power Supply?
Common mode choke is sometimes called common-mode choke because its function is to suppress it. It is often used in switching power supply circuits to form various filters to filter EMI and suppress the electromagnetic waves generated by diverous high-speed signals from emitting outwards. As shown in the following figure, there are a group of parallel lines in the circuit, and normal signals are basically unaffected when they pass through. Men, när common-mode current flows, due to the same direction of common-mode current, it will generate a magnetic field in the coil and increase the inductance of the coil, making the coil appear as high impedans.
1. Schematisk diagram av signal passering genom vanligt läge choke.
Schematisk diagram av den front stage of switching power supply, in which L1 is common mode choke. In order to suppress common-mode interference, we know that common-mode signal is a signal with equal amplitude and phase, and the noise it produces is ground noise, which is the noise of two wires respektive. After understanding the common-mode noise, we will know why common mode choke is connected to the AC side.
