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Common-mode inductor and differential mode inductor, respectively, have what use?

by:Transmart     2020-05-29
The design of the power supply filter usually from two aspects of common mode and differential mode. Important part of the common mode filter is a common mode choke coil, compared with the differential mode choke, common mode choke a significant advantage lies in its inductance value is extremely high, and small volume, the design of common mode choke when an important question to consider is the leakage inductance of the it, also is the differential mode inductance. Usually, the leakage inductance of the calculation method is to assume that it is 1% of the common-mode inductor, actually the leakage inductance of common-mode inductance of 0. Between 5% ~ 4%. In the design of the optimal performance of the reactor, the effect of this error may be nots allow to ignore. The importance of the leakage inductance. The leakage inductance is how? Tightly winding, and around a week full of toroidal coil, even without core, all of its magnetic flux is concentrated in the coil in the 'core'. However, if the toroid not around a week, or not close, the flux will leak out from the core. The effect to line the relative distance between the coils and the spiral tube is directly proportional to the magnetic permeability of the core. Common mode choke coil has two winding, the two winding is designed to make them of the current flow through to the core conduction along the coil in the opposite direction, so that the magnetic field is zero. If to be on the safe side, the core body on the coil is not double winding, so there is a considerable gap between the two winding, naturally caused flux 'leak', it is said that the magnetic field is concerned with is not really the point of 0. Common mode choke is the leakage inductance of the differential mode inductance. In fact, related to the differential mode flux must leave at a certain point the core body, in other words, the magnetic flux in core body external form closed loops, and not just confined to the ring core body. If the core body has a differential mode inductance, so, differential mode current will be deviation from zero in the core of magnetic flux in the body, if the deviation is too large, the core body and magnetic saturation phenomenon happens, the common-mode inductor with coreless induction. As a result, the common-mode radiation intensity like circuit didn't choke. Common mode choke in filter design, common mode and differential mode of the two parts is supposed to be independent of each other. The two parts are not truly independent, however, because the common mode choke can provide considerable differential mode inductance. This part of the differential mode inductance can be made of discrete differential mode inductance to simulate. To take advantage of differential mode inductance, in the design process of the filter, common mode and differential mode should not be at the same time, which should be done in a certain order. First of all, should measure the common-mode noise and filter to remove it. By using differential mode suppression network ( 差模抑制网络) And differential mode components can be eliminated, thus can directly measure the common-mode noise. If the design of common mode filter to make the differential mode noise at the same time does not exceed the permitted range, then it should be a mixture of common mode and differential mode noise measurement. Because known common-mode component under noise tolerance, so the standard is only differential mode of composition, the available of the leakage inductance of the differential mode to common mode filter attenuation. For low power supply system, common mode choke the differential mode of inductance is enough to solve the problem of differential mode radiation, because the source of differential mode radiation impedance is small, so only a tiny amount of inductance is effective.
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