Absorption magnetic ring, also known as ferrite magnetic ring, short for magnetic ring. It is a commonly used anti-interference element in electronic circuits and has a good inhibiting effect on high frequency noise. It is generally made of ferrite material (mn-zn). The magnetic ring has different impedance characteristics at different frequencies. Generally, the impedance is small at low frequencies. As you all know, the higher the signal frequency, the easier radiation (buy high-quality computer case is also to reduce the electromagnetic leakage), and general signal lines are no shielding layer, then the signal is very good antenna, receiving all kinds of clutter in the surrounding environment of high frequency signals, and the signal superimposed on the original transmission signal, useful signals may even change the original transmission. Under the action of magnetic ring, the normal and useful signal can pass well, and the high frequency interference signal can be suppressed well, and the cost is low.
By passing the whole cable through a ferrite magnetic ring, a common-mode choke is formed. The cable can also be wound around the magnetic ring for several turns as required. The higher 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 practical engineering, the number of turns of magnetic ring should be adjusted according to the frequency characteristic of interference current. Usually, when the frequency band of the interference signal is wide, two magnetic rings can be set on the cable, each magnetic ring can surround a different number of turns, which can suppress both high-frequency interference and low-frequency interference at the same time. From the mechanism of common mode choke, the higher the impedance, the more obvious the interference suppression effect. The impedance of the common-mode choke is from the common mode inductor Lcm=jwLcm. It is not hard to see from the formula that the greater the inductance of the magnetic ring for a certain frequency of noise, the better. This is not the case, because the actual magnetic ring has parasitic capacitors, which exist in parallel with the inductor. When the high frequency interference signal is encountered, the capacitance resistance is small, and the inductance of the magnetic ring is short-circuited, which makes the common mode choke useless.