A brief analysis of the role of resonant inductor & Definition and working principle of common mode

A brief analysis of the role of resonant inductance

Role of resonant inductor:

1. Resistance to current: the self-induced electromotive force in the coil is always in opposition to the current change in the coil.It can be divided into high frequency choke coil and low frequency choke coil.

2. Tuning and frequency selection: inductance coil and capacitor in parallel can form LC tuning circuit.In resonance, since the inductive reactance of the circuit is equal to and opposite to the capacitive reactance, the inductive reactance of the total circuit current is the minimum and the current flow is the maximum (referring to the ac signal of f=f0). Therefore, LC resonant circuit plays the role of frequency selection and can select the ac signal of a certain frequency .

Definition and working principle of common mode inductance

Common mode Choke, also known as Common mode Choke, is used to filter Common mode emi signals in the switching power supply of computers.In the design of the board, the common-mode inductance also ACTS as an EMI filter, which is used to suppress the electromagnetic wave emitted from the high-frequency signal.

Common mode inductance filter circuit, La and Lb are common mode inductance coil.The two coils are wound on the same core with the same number of turns and the same phase (in reverse).In this way, when the normal current in the circuit flows through the common-mode inductance, the current in the inductance coil wound in the same phase generates the opposite magnetic field and cancelling each other out. At this time, the normal signal current is mainly affected by the coil resistance (and a small amount of damping caused by the leakage sense).When the common mode current flows through the coil, due to the homogeneity of the common mode current, the magnetic field in the same direction will be generated in the coil and the inductive reactance of the coil will be increased. As a result, the coil will show high impedance and strong damping effect will be generated, so as to attenuate the common mode current and achieve the purpose of filtering.

In fact, if the filter circuit is connected to the interference source at one end and the interfered equipment at the other end, then La and C1, Lb and C2 constitute two sets of low-pass filters, which can control the common mode EMI signal on the circuit at a very low level.The circuit can not only suppress the incoming EMI signal from the outside, but also attenuate the EMI signal produced by the circuit itself, which can effectively reduce the EMI interference intensity.

A small common mode inductance produced in China, adopting high frequency noise suppression countermeasure, common mode choke coil structure, no attenuation of signal, small size, easy to use, good balance, easy to use, high quality and so on.It is widely used in double balance tuning device, multi-frequency transformer, impedance transformer, balance and unbalanced conversion transformer...And so on.

There is a kind of common mode filter inductor/EMI filter inductor using ferrite core, and bifilar winding countermeasures of noise suppression, high common mode noise suppression and low differential mode noise suppression, suppress interference sources and low differential mode noise signal in the high frequency signal is difficult to deformation, small volume, it has good balance, the advantages of convenient use and high quality.Widely used in suppressing EMI noise of electronic equipment, USB circuit of personal computer and peripheral equipment, DVC, IEEE1394 circuit of STB, LCD display panel, low-voltage differential signal...And so on.