What is the function of transformer core?

Usually, the magnetic ring is seen at one or both ends of the power line or signal line of the electronic device, which is the 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 operating signal is a differential mode signal), so it is simple to use without considering the problem of signal distortion.

And the common mode choke does not need to be grounded, it can be added directly to the cable.

The number of turns of the magnetic ring is selected to pass the entire cable through a ferrite magnetic ring to form a common mode choke.

If desired, the cable can also be wrapped around the magnetic ring several times. The more turns,

The better the interference suppression effect for lower frequencies, while the weaker the noise suppression effect for higher frequencies.

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 interfering signal is wide, two magnetic rings can be put on the cable, and each magnetic ring has a different number of turns.

This suppresses both high-frequency and low-frequency interference. From the perspective of the mechanism of the action of the common-mode choke, the greater its impedance,

The more obvious the effect on interference suppression. The impedance of the common-mode choke comes from the common-mode inductor Lcm=jwLcm It is not difficult to see from the formula,

For noise at a certain frequency, the greater the inductance of the magnetic ring, the better. But this is not the case, because there are parasitic capacitors on the actual magnetic rings.

The way of existence is parallel with the inductor. When encountering a high-frequency interference signal, the capacitance of the capacitor is small, which short-circuits the inductance of the magnetic ring.

Thus, the common mode choke is 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 --- of thousands of people, while that of nickel-zinc ferrite is in the hundreds --- thousands.

The higher the permeability of ferrite, the greater its impedance at low frequencies and the smaller its impedance at high frequencies. Therefore, when suppressing high-frequency interference, nickel-zinc ferrite should be used;

On the contrary, manganese-zinc ferrite is used. Or the same bundle of cables is covered with manganese-zinc and nickel-zinc ferrite at the same time, so that the interference frequency band can be suppressed is wider.

The larger the difference between the inner and outer diameters of the magnetic ring, the greater the longitudinal height, and the greater its impedance, but the inner diameter of the magnetic ring must be tightly wrapped around the cable to prevent magnetic leakage.

The device position of the magnetic ring should be as close as possible to the source of interference, that is, it should be close to the inlet and outlet of the cable

The magnetic ring seen at one or both ends is the 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 the differential mode signal)

Therefore, it is simple to use without considering signal distortion. And the common mode choke does not need to be grounded, it can be added directly to the cable.

Principles of use of magnetic cores:
1 The longer the magnetic ring, the better

2 The tighter the bore diameter and the cable passed through, the better.

3 When the low-frequency end is harassed, it is recommended to wrap the cable around 2~3 turns, and when the high-frequency end is harassed, it cannot be wound

(Because of the existence of distributed capacitors, a longer magnetic ring is chosen.)