The difference between inductor core and iron core
The inductor core is a reactor using an iron core, which is small in size and uses less copper.
Due to the nonlinearity of the ferromagnetic material, its inductance is basically unchanged when the passing current is small, but it will decrease when the passing current is large, and the current and voltage are not linearly related. In order to reduce this nonlinearity, an air gap is often opened in the core magnetic circuit.
Inductor cores, the magnetic rings we usually see at one or both ends of the power line or signal line of electronic equipment are common mode choke coils. The common mode choke coil can form a large impedance to the common mode interference current, but has no effect on the differential mode signal (the working signal is a differential mode signal), so it is easy to use without considering the problem of signal distortion. And the common mode choke coil does not need to be grounded and can be directly added to the cable. Selection of the number of turns of the magnetic ring Passing the cable through a ferrite magnetic ring constitutes a common mode choke coil, and the cable can also be wound on the magnetic ring for several turns as required. The more the number of turns, the better the interference suppression effect on the lower frequency, and the weaker the noise suppression effect on the higher frequency. In actual engineering, the number of turns of the magnetic ring should be adjusted according to the frequency characteristics of the interference current. Usually when the frequency band of the interference signal is wide, two magnetic rings can be placed on the cable, and each magnetic ring has a different number of turns, so that high-frequency interference and low-frequency interference can be suppressed at the same time. From the perspective of the mechanism of the common mode choke coil, the greater the impedance, the more obvious the interference suppression effect. The impedance of the common mode choke comes from the common mode circuit
Lcm=jwLcm, it is not difficult to see from the formula that for a certain frequency of noise, the larger the inductance of the magnetic ring, the better. But the actual situation is not the case, because there is also a parasitic capacitance on the actual magnetic ring, which exists in parallel with the inductance. When encountering a high-frequency interference signal, the capacitive reactance of the capacitor is small, and the inductance of the magnetic ring is short-circuited, so that the common mode choke coil loses its effect. According to the frequency characteristics of the interference signal, nickel-zinc ferrite or manganese-zinc ferrite can be selected, and the high-frequency characteristics of the former are better than the latter. The magnetic permeability of manganese-zinc ferrite is several thousand-tens of thousands, while that of nickel-zinc ferrite is hundreds-thousands. The higher the permeability of ferrite, the greater its impedance at low frequencies and the smaller its impedance at high frequencies. Therefore, when suppressing high-frequency interference, nickel-zinc ferrite should be used; otherwise, manganese-zinc ferrite should be used. Or put manganese zinc and nickel zinc ferrite on the same bundle of cables at the same time, so that the interference frequency band that can be suppressed is wider. The greater the difference between the inner and outer diameters of the magnetic ring, the greater the longitudinal height, and the greater its impedance, but the inner diameter of the magnetic ring must tightly wrap the cable to avoid magnetic flux leakage. The installation position of the magnetic ring should be as close as possible to the source of interference, that is, it should be close to the entrance and exit of the cable.
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