Current transformer manufacturers explain the function and working principle of common mode inductance in detail -
1. The function and principle of common mode inductors I believe that many people are familiar with common mode inductors, but do you fully understand its connection method? Are the common mode inductors on your circuit connected correctly? First of all, let's get to know the common mode inductor. Common mode inductor is a common mode interference suppression device with ferrite as the core. It is composed of two coils with the same size and the same number of turns symmetrically wound on the same ferrite ring core to form a four-terminal Devices, common mode inductance play a role in hindering the alternating current. For plug-in inductors, we generally see UU type, EE type and ring type. Under a certain AC frequency, the larger the inductance, the greater its resistance to alternating current. On the contrary, the smaller the inductance, the smaller the resistance. It suppresses common-mode signals in the circuit, and the inductance of common-mode inductors can be used. bridge to measure. Second, the application of common mode inductors in switching power supplies 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. Suppresses the outward emission of electromagnetic waves generated by various high-speed signals, as shown in the figure below, there is a group of parallel lines in the circuit, and the normal signal is basically not affected when it passes through, but when there is a common-mode current flowing through it, due to the isotropy of the common-mode current, A magnetic field in the same direction will be generated in the coil to increase the inductive reactance of the coil, so that the coil exhibits high impedance and produces a strong damping effect. At this time, the common mode current will be attenuated to achieve the purpose of suppressing interference. 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.