Explain how the common mode inductor is connected to the AC side of the switching power supply?1

1. The function and basic principle of common mode inductors must be familiar to many people about common mode inductors, but do you have a thorough understanding of its wiring method? Is the common mode inductor on your power circuit connected correctly? The first step is to understand the common mode inductor. Common mode inductance is a common mode influence suppression component with a ferrite core as the transformer skeleton. It consists of two electromagnetic coils with the same specifications and the same number of coil turns. The coil inductance is symmetrical in the same ferrite core ring. On the skeleton of the transformer, a four-terminal component is generated, and the common mode inductance has the effect of blocking the AC circuit. Regarding software inductors, the most commonly seen ones are UU type and EE type and their toroidal shapes. Under a certain AC frequency, the larger the inductance, the greater the blocking ability of the AC current, and the smaller the inductance, the smaller the blocking ability. It suppresses the common mode data signal in the power supply circuit, and the common mode inductance The inductance value can be accurately measured with a power bridge.

Second, the application of common mode inductance in switching power supply Common mode inductance is sometimes called common mode choke coil, because it has the function of suppressing, it is mostly used in switching power supply circuit, forming various filters to filter EMI It can suppress the radio waves caused by various high-speed data signals from being sent out. As shown in the figure below, there is a set of parallel processing routes in the power supply circuit. All normal data signals are basically not affected under the circumstances, but when there is a common mode current When flowing, because of the same direction of the common mode current, it will cause the electromagnetic field in the same direction in the electromagnetic coil and expand the inductive reactance of the electromagnetic coil, so that the electromagnetic coil mainly exhibits high characteristic impedance, resulting in a strong actual effect of vibration reduction. At this moment, the amount of common mode current will be attenuated by the attenuation factor, so as to suppress the influence. The following figure is the schematic diagram of the front part of the switching power supply, in which L1 is the common mode inductor to suppress the common mode effect. We know that the common mode data signal is a data signal with the same strength and the same phase difference, and the noise it causes is grounded Noise is the noise of the two wires to the ground. If you understand the common mode noise, you will understand the common mode inductance, and then you will understand why the common mode inductance will be connected to the AC side.