Application of common mode inductors in switching power supplies?
A common mode choke, also known as a common mode choke, is a symmetrical winding of coils with opposite directions and the same number of turns on a closed magnetic ring. The ideal common mode choke has a suppressing effect on common mode interference between L (or N) and E, while it has no inductive suppressing effect on differential mode interference between L and N. However, incomplete symmetry in the actual coil winding can lead to the generation of differential mode leakage inductance. When signal current or power current flows through two windings in opposite directions, the generated magnetic flux cancels each other out, and the choke coil exhibits low impedance. When the common mode noise current (including the disturbance current caused by the ground loop, also known as longitudinal current) flows through two windings in the same direction, the magnetic flux generated is added in the same direction, and the choke coil presents high impedance, thereby suppressing common mode noise.
Common mode inductor is essentially a bidirectional filter: on the one hand, it needs to filter out common mode electromagnetic interference on the signal line, and on the other hand, it needs to suppress itself from emitting electromagnetic interference to avoid affecting the normal operation of other electronic devices in the same electromagnetic environment.
The common mode choke can transmit differential mode signals, both DC and low-frequency differential mode signals can pass through, and it presents a large impedance for high-frequency common mode noise, so it can be used to suppress common mode current interference.
Common mode inductor, sometimes also known as common mode choke, is used to suppress and is commonly used in switching power supply circuits. It forms various filters to filter EMI and suppress the emission of electromagnetic waves generated by high-speed signals. As shown in the figure below, there is a set of parallel lines in the circuit. Normal signals are not affected when passing through, but when a common mode current flows through, due to the homogeneity of the common mode current, a magnetic field in the same direction is generated in the coil, increasing the inductance of the coil and making it appear high impedance, producing a strong damping effect. At this time, the common mode current will be attenuated to achieve the purpose of suppressing interference.
