Common mode inductor applications in switching power supplies?
Common Mode Choke (Common mode Choke), also known as common mode choke coil, is a coil with opposite directions and the same number of turns symmetrically wound on a closed magnetic ring. The ideal common mode choke coil has a suppression effect on the common mode interference between L (or N) and E , but has no inductive suppression effect on the differential mode interference existing between L and N . However, the incomplete symmetry of the actual coil winding will lead to the generation of differential mode leakage inductance. When the signal current or power current flows in the opposite direction in the two windings, the generated magnetic flux cancels each other, and the choke coil presents low impedance. The common mode noise current (including the disturbance current caused by the ground loop, also known as the longitudinal current) flows in the same direction when passing through the two windings, and the generated magnetic flux is added in the same direction, and the choke coil presents high impedance, thereby suppressing the common The effect of mode noise.
The common-mode inductor is essentially a two-way filter: on the one hand, it needs to filter out the common-mode electromagnetic interference on the signal line, and on the other hand, it must restrain itself from emitting electromagnetic interference to avoid affecting the normal operation of other electronic devices in the same electromagnetic environment. .
The common mode choke coil can transmit differential mode signals, both DC and low frequency differential mode signals can pass through, but it presents a large impedance to high frequency common mode noise, so it can be used to suppress common mode current disturbance.
Application of common mode inductor in switching power supply?
Common-mode inductors are sometimes called common-mode choke coils, because their function is to suppress, and they are mostly used in switching power supply circuits to form various filters to filter EMI and suppress electromagnetic waves generated by various high-speed signals from going outward. Transmission, as shown in the figure below, there is a group of parallel lines in the circuit, and the normal signal is basically unaffected when passing through, but when there is a common mode current flowing through, due to the isotropy of the common mode current, a magnetic field in the same direction will be generated in the coil. Increase the inductive reactance of the coil to make the coil exhibit high impedance and produce a strong damping effect. At this time, the common mode current will be attenuated to achieve the purpose of suppressing interference.
1. Schematic diagram of the signal passing through the common mode inductor
The following figure is the schematic diagram of the front stage of the switching power supply, where L1 is the common mode inductor. In order to suppress the common mode interference, we know that the common mode signal is a signal with equal amplitude and the same phase, and the noise it generates is ground noise, which is two The noise of the root wires to the ground respectively. If we understand the common mode noise, we will know the common mode inductor and why the common mode inductor will be connected to the AC side.
