Common Mode Choke

Common-mode choke, also known as the common mode choke coil, used in the switch power filter in the common mode of computer electromagnetic interference signals. In the board design, common-mode inductor is also plays a role of EMI filter, used to suppress the signal produced by electromagnetic radiation emission outward.

Common-mode inductor filter circuit, La and Lb is common mode inductor. The two coil around the same core, phase are the same number of turns and wire (the reverse). So, when the normal current flows through the common-mode inductance in the circuit, the current in the same phase winding inductance coil magnetic field generated in reverse and cancel each other out, as normal signal current is mainly influenced by coil resistance (and a small amount of damping) caused by the leakage inductance of the; When there is a common mode of electric

Flow through the coil, as a result of the common-mode current ecotropic, would produce in the coil magnetic field direction and increase the coil impedance, the coil performance for high impedance, the stronger damping effect, this attenuation common-mode current, achieve the goal of filtering.

Answer the interference sources, in fact, the filter circuit end at the other end to be interference devices, La and C1, Lb and C2 form two groups of low pass filter, can make the common mode EMI signal is on the line control on a low level. This circuit can inhibit the external EMI incoming signal, and attenuation line EMI signals generated by their own work, can effectively reduce EMI interference intensity.

Domestic production of a small common mode inductor, USES the high frequency noise suppression countermeasure, common mode choke coil structure, signal attenuation, small volume, easy to use, it has good balance, the advantages of convenient use and high quality. Widely used in the double balanced mixer device, multiple frequency transformer, impedance transformer, balance and imbalance of switching 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 is difficult to deformation in the high speed signal, small volume, it has good balance, the advantages of convenient use and high quality. Widely used in electronic equipment EMI noise control, personal computers and peripherals USB line, DVC, STB IEEE1394 circuit, liquid crystal display panels, low voltage differential signal... And so on.

The leakage inductance of the differential mode

For the ideal inductance model, when after the coil winding, all flux are concentrated in the center of the coil. But not usually toroidal coil around a week, or not close, this will cause magnetic flux leakage. Common-mode inductor have two windings, which has quite

Common-mode inductor

Big gap, so it will produce magnetic flux leakage, and differential mode inductor is formed. Therefore, common-mode inductor are also typically have a certain differential mode interference attenuation ability.

In the design of filter, we can also use the leakage inductance. As in ordinary filter, only install a common-mode inductor, caused by the leakage inductance of the common-mode inductance of the right amount of differential mode inductance, have inhibitory effect on current differential mode. Sometimes, but also for increase the leakage inductance common-mode choke coil, increase the amount of differential mode inductance, in order to achieve better filtering effect.

Material quality

The circular type of core strengths:

High initial permeability (this is the basic requirement of common mode inductance), high saturation magnetic induction intensity, temperature than ferrite (small) can be understood as temperature rise, stable frequency characteristic is more flexible, because of the high permeability, small can make a lot of sense, to adapt to the wide frequency comparison;

Advantage:

Because the initial permeability is 5 to 20 times of ferrite, the inhibitory effect of conduction interference than ferrite;

Nanocrystals of high saturation magnetic induction intensity is better than ferrite, so in the big power flow is not easy to saturation;

Temperature rise is much lower than the UF series, I actual test: nearly 10 degrees lower at room temperature (individual test values for reference only);

Structural flexibility to make its good adaptability, to change from the processing craft, can adapt to different requirements (seen on energy-saving lamps use magnetic ring inductance, use quite flexible);

Distributed capacitance will be smaller, because the area of the winding is more wide, the volume is relatively small;