It is commonly used in electronic circuit anti-interference components, for high frequency noise has a good inhibition effect, generally used ferrite material (Mn-Zn) made. The magnetic ring has different impedance characteristics at different frequencies. Generally, the impedance is very small at low frequency. When the signal frequency increases, the impedance of the magnetic ring increases sharply. As we all know, the higher the signal frequency, the easier it is to radiate out (to buy a high-quality computer case is also to reduce electromagnetic leakage), and the general signal lines are not shielded layer, then these signal lines become a good antenna, receive all kinds of clutter in the surrounding environment of high frequency signals, and these signals superimposed on the original transmission of signals, It might even change the useful signal that was transmitted. So under the action of the magnetic ring, the normal useful signal is very good through, but also very good to inhibit the passage of high-frequency interference signal, and the cost is low.

A common mode choke is formed by running the entire cable through a ferrite ring, which can be wound several turns as needed. The greater the number of turns, the better the suppression effect is for the lower frequency interference, while the weaker the suppression effect is for the higher frequency noise. In practical engineering, the number of turns of magnetic ring should be adjusted according to the frequency characteristics 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 circle around a different number of turns, so that high frequency interference and low frequency interference can be suppressed at the same time. From the mechanism of common mode choke, the larger the impedance, the more obvious the interference suppression effect. The impedance of the common-mode choke comes from the common-mode inductance Lcm=jwLcm. It is not difficult to see from the formula that, for noise of a certain frequency, the larger the inductance of the magnetic ring, the better. But this is not the case, because the actual ring also has a parasitic capacitor, which exists in parallel with the inductor. When the high frequency interference signal is encountered, the capacitive reactance is small, and the inductance of the magnetic ring is short circuited, so that the common mode choke will lose its function.