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Common mode inductor of magnetic loop inductor
Jul 07, 2017



Common mode inductor of magnetic loop inductor


The inductor is an energy storage component for power filter circuits, and the magnetic loop inductor is no exception, but the magnetic loop inductance focuses on suppressing conductive interference. The common mode inductor is strictly a magnetic ring inductor. The common mode inductor consists of a soft magnetic core and two sets of coils wound in the same direction, as shown in the following figure. For the differential mode signal, since the magnetic fields generated by the two sets of coils are opposite in direction, they cancel each other out, and the iron core is not magnetized, and does not inhibit the signal. For the common mode signal, since the magnetic fields generated by the two sets of coils are not canceled but superimposed on each other, the iron core is magnetized. Due to the high magnetic permeability of the core material, the core will generate a large inductance, and the impedance of the coil will suppress the passage of the common mode signal.


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Common mode noise is mainly generated when various switching devices are turned on and off, and can be decomposed into different harmonic forms with a relatively wide spectral range. For interference signals below 30MHz, it is generally transmitted by conduction. In order to filter the common mode interference more effectively, the common mode inductor should first have a sufficiently large inductance. Therefore, the high magnetic permeability of the core material is the most basic requirement for the common mode inductance. On the other hand, the frequency characteristics of the core material are also a key factor in determining device performance. Since common mode interference has a wide spectrum, the impedance of the core to common mode interference has a maximum value only in a certain frequency band. Therefore, in order to filter out common-mode interference in a certain band, the core frequency characteristics should make the impedance of the device have the largest mismatch with the subsequent circuits in this band, so as to generate sufficient loss for common mode interference (called insertion loss). ). For common mode signals, the common mode inductanc


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