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The inductor core is a reactor using an iron core, which is small in size and uses less copper.
Due to the non-linearity of ferromagnetic materials, the inductance of the ferromagnetic material is basically unchanged when the passing current is small, but will decrease when the passing current is large, and the current and voltage are not linear. In order to reduce this nonlinearity, an air gap is often opened in the core magnetic circuit.
Inductor core, the magnetic ring we usually see at one or both ends of the power line or signal line of electronic equipment is a common mode choke.
The common mode choke 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 simple to use without considering the signal distortion. And the common mode choke does not need to be grounded and can be directly added to the cable. Selection of the number of turns of the magnetic ring Pass the cable through a ferrite magnetic ring to form a common mode choke coil. According to the needs, the cable can also be wound several turns on the magnetic ring. The more the number of turns, the better the suppression effect on lower frequency interference, and the weaker the suppression effect on higher frequency noise. 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 relatively wide, two magnetic rings can be put 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 point of view of the mechanism of the common mode choke coil, the larger the impedance, the more obvious the interference suppression effect. The impedance of common mode chokes comes from the common mode.
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 are parasitic capacitances on the actual magnetic ring, which exists in parallel with the inductance. When encountering high-frequency interference signals, the capacitive reactance of the capacitor is small, which short-circuits the inductance of the magnetic ring, thereby making the common mode choke ineffective. According to the frequency characteristics of the interference signal, nickel-zinc ferrite or manganese-zinc ferrite can be selected. The high frequency characteristics of the former are better than the latter. The permeability of manganese-zinc ferrite is in the thousands --- tens of thousands, while the permeability of nickel-zinc ferrite is in the hundreds ---thousands. The higher the permeability of ferrite, the greater the impedance at low frequencies and the smaller the 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 cable 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 and the greater the longitudinal height, the greater the impedance, but the inner diameter of the magnetic ring must be tightly wrapped around the cable to avoid magnetic leakage. The installation position of the magnetic ring should be as close to the interference source as possible, that is, it should be close to the inlet and outlet of the cable.
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