1、 The absorption filter composed of motor magnetic rings should not only use high permeability lossy materials, but also exhibit a resistance of about ten to several hundreds to high-frequency components in the circuit. Therefore, its role in high impedance circuits is not obvious. On the contrary, it will be very effective when used in low impedance circuits (such as power distribution, power supply, or RF circuits).
2、 In the high frequency range (greater than 10MHz), the inductance of the motor magnetic ring remains very small, while the impedance is large, which causes the energy of the high-frequency signal to be converted into heat and dissipated when passing through the magnetic material, thus hindering the passage of high-frequency signals and suppressing their interference. The optimal suppression frequency range is usually related to the ferrite suppression element. Generally, the higher the magnetic permeability, the lower the suppression frequency, and the larger the ferrite volume, the better the suppression effect. When the volume is constant, the longer and thinner the shorter and thicker the better the suppression effect, and the smaller the internal force, the better the suppression effect.
3、 The magnetic ring of the motor has different impedance characteristics at different frequencies. Generally, the impedance is very small at low frequencies, and sharply increases at high frequencies. The higher the signal frequency, the easier it is for the magnetic field to radiate out. Generally, signal lines are unshielded, such as the CAN bus I am using now. These signal lines become a perfect antenna that constantly receives high-frequency signals around it. The superposition of these signals changes the actual signal to be transmitted. The magnetic ring can effectively transmit useful signals while suppressing high-frequency interference signals.
4、 When the motor magnetic ring suppresses common mode signal interference, the magnetic ring can pass the signal (connected differential signal line) or power line (positive and negative lines) through it at the same time. To increase the effect, it can be symmetrically wound around the magnetic ring several times to increase inductance and enhance the absorption effect of common mode signals. However, it has no effect on differential signals. The components should be installed near the interference source. For input and output circuits, they should be installed as close as possible to the inlet and outlet of the shielding box.
