Common mode inductors Common mode Choke

Product Introduciton：

Common mode inductor (common mode choke), also known as common mode choke, is commonly used in computer switching power supply to filter common mode EMI signal. In the design of the circuit board, the common mode inductor also plays the role of EMI filtering, which is used to suppress the electromagnetic wave radiated by the high-speed signal line.

Common mode inductor filter circuit, La and LB are common mode inductor coils. The two coils are wound around the same iron core with the same number of turns and phase (reverse winding). In this way, when the normal current in the circuit flows through the common-mode inductor, the current creates a reverse magnetic field in the inductor coil wound in the same phase, which cancels each other out. At this point, the normal signal current is mainly affected by the coil resistance (and a small amount of damping due to leakage); When the common mode current flows through the coil, due to the isotropy of the common mode current, the magnetic field in the same direction will be generated in the coil, increasing the induction reactance of the coil, making the coil have the characteristics of high impedance, generating strong damping effect, thus attenuating the common mode current and achieving the purpose of filtering.

In fact, if one end of the filter circuit is connected to the interference source and the other end is connected to the interfered device, then La and C1, LB and C2 constitute two sets of low-pass filters, which can control the common mode EMI signal on the line at a very low level. This circuit can not only suppress the external EMI signal, but also can attenuate the EMI signal generated by the line itself, effectively reducing the intensity of EMI interference.

The domestic small common mode inductor has the advantages of high frequency noise suppression, common mode choke structure, no signal attenuation, small size, easy to use, good balance, easy to use and high quality. It is widely used in double balance tuning device, multi-frequency transformer, impedance transformer, balanced and unbalanced transformation transformer, etc.

Features

1. （1） The wires around the coil core should be insulated to ensure that the coil does not break down and short circuit between turns under instantaneous overvoltage.；
2. （2） When the coil flows through the instantaneous high current, the magnetic core should not be saturated；
3. （3） The magnetic core in the coil should be insulated from the coil to prevent breakdown between the coils under instantaneous overvoltage；
4. （4） The coil should be wrapped in a single layer as far as possible, which can reduce the parasitic capacitance of the coil and improve the ability of the coil to withstand transient overvoltage.

In general, we should also be careful to select the frequency band to filter. The larger the common-mode impedance, the better. Therefore, when selecting a common mode inductor, you need to look at the device data, mainly based on the impedance frequency curve. In addition, attention should be paid to the effect of differential mode impedance on the signal, especially on high-speed ports