The principle and function of ferrite magnetic ring anti-interference magnetic ring
The transmission line of digital equipment has a cylindrical shape. What is this? It is a magnetic ring, an anti-interference magnetic ring, or an absorbing magnetic ring, a ferrite magnetic ring.
Why set up anti-jamming magnetic ring? The motherboard, CPU, power supply, and IDE data cable in the computer case all work at a very high frequency, so there are a lot of stray electromagnetic interference signals in the case, and the signal strength is also several times to several times outside the case. ten times! USB cables without magnetic loops are not shielded in this space, then these USB cables become good antennas to receive various messy high-frequency signals in the surrounding environment, and these signals are superimposed on the originally transmitted signals. It may even change the useful signal originally transmitted, which is prone to problems.
In order to improve the transmission rate and stability, and to reduce the interference of the transmission line to other devices, such as sound cards, when transmitting data, an electrostatic shielding layer is designed. The shielding layer is made of a thin metal foil or multiple strands of thin copper wires woven into a mesh, using the principle of surface effects of electrostatic fields. That is, wrap the outer surface of the data transmission line with a layer of metal film, and ground the shielding layer with the chassis, and the data line can be well isolated from the space interference signal!
Absorbing magnetic ring, also known as ferrite magnetic ring, is often used as a detachable magnetic ring for separation. It is a commonly used anti-interference component in electronic circuits. It has a good suppression effect on high-frequency noise. Generally, ferrite materials are used. (Mn-Zn) made. The magnetic ring has different impedance characteristics at different frequencies. Generally, the impedance is very small at low frequencies. When the signal frequency increases, the impedance of the magnetic ring increases sharply. It can make normal useful signals pass well, and can well suppress the passing of high-frequency interference signals, and the cost is low.
Ferrite anti-jamming core characteristics:
The ferrite anti-interference magnetic core is a new type of low-cost and high-quality interference suppression device developed in recent years. Its function is equivalent to a low-pass filter, which can better solve the high-frequency interference suppression of power lines, signal lines and connectors. Problems, and has a series of advantages such as easy to use, convenient, effective, and small space. Using ferrite anti-interference core to suppress electromagnetic interference (EMI) is an economical, simple and effective method, which has been widely used in computers and other Military or civilian electronic equipment.
Ferrite is a kind of high-permeability material infiltrated with one or more other metals such as magnesium, zinc, nickel and sintered at 2000 ℃. In the low frequency range, the ferrite anti-interference magnetic core shows very low inductance. The impedance value does not affect the transmission of useful signals on the data line or signal line. In the high frequency band, starting from about 10MHz, the impedance increases, its inductive component remains small, but the resistive component increases rapidly. When high-frequency energy passes through the magnetic material, the resistive component will convert this energy Dissipate heat energy. In this way, a low-pass filter is formed, so that the high-frequency noise signal has a large attenuation, and the impedance of the low-frequency useful signal can be ignored, and the normal operation of the circuit is not affected.
The EMI absorption ring/bead is a component made of ferrite, which is a loss-absorbing component. Its characteristics are as follows: it absorbs high-frequency signals and converts the absorbed energy into thermal energy to dissipate, so as to suppress the transmission of high-frequency interference signals along the wire. The resistance component of the equivalent impedance is a function of frequency. And change.
The effective frequency band of the EMI absorption ring/bead is 2 1000 MHz, and the frequency band with the best performance is 5 200 MHz. In this frequency band, the absorption impedance is maintained as a constant.
When selecting EMI absorption ring/beads, please pay attention: the magnitude of the passing current is proportional to the volume of the component, and the two are out of adjustment, which may cause saturation and reduce the performance of the component. An effective way to avoid saturation is to connect the two wires of the power supply (positive, negative or fire, ground ) Pass through a magnetic ring at the same time. Another better way to use the magnetic ring is to make the wires passing through the magnetic ring string repeatedly, which can increase the area through the ring and increase the equivalent absorption length. Second, make full use of the magnetic hysteresis of the magnetic ring. Features, improve low-end characteristics.
Its manufacturing process and mechanical properties are similar to ceramics. Its electromagnetic properties are related to the addition of metal components and the time during the sintering process, and the temperature is related to the gas composition. Separately mounted magnetic rings should be used as far as possible to choose a magnetic ring with a smaller inner diameter and longer length. At the same time, the magnetic ring must tightly wrap the cable, that is, the inner diameter of the magnetic ring should be closely matched with the outer diameter of the cable.
Why set up anti-jamming magnetic ring?
The motherboard, CPU, power supply, and IDE data cable in the computer case all work at a high frequency, so there is a large amount of stray electromagnetic interference signals in the case, and the signal strength is also several times to several times outside the case. ten times! Absorbing magnetic ring, also known as ferrite magnetic ring, is often used in detachable separate magnetic ring. It is a commonly used anti-interference component in electronic circuits. It has a good inhibitory effect on high-frequency noise. Generally, ferrite materials are used. (Mn-Zn) made. The magnetic ring has different impedance characteristics at different frequencies. Generally, the impedance is very small at low frequencies. When the signal frequency increases, the impedance of the magnetic ring increases sharply. It can make normal useful signals pass well, and can well suppress the passing of high-frequency interference signals, and the cost is low.
Ferrite is a ferrimagnetic material with a cubic lattice structure. The ferrite material is iron-magnesium alloy or iron-nickel alloy. Its manufacturing process and mechanical properties are similar to ceramics, and its color is gray-black. One type of magnetic core often used in electromagnetic interference filters is ferrite materials, and many manufacturers provide ferrite materials specifically for electromagnetic interference suppression. The characteristic of this material is that the high frequency loss is very large, and it has a high magnetic permeability. It can be the smallest capacitance generated between the coil windings of the inductor under the condition of high frequency and high resistance. For ferrites used to suppress electromagnetic interference, the most important performance parameters are permeability μ and saturation magnetic flux density Bs. Permeability μ can be expressed as a complex number, the real part constitutes the inductance, and the imaginary part represents the loss, which increases as the frequency increases. Therefore, its equivalent circuit is a series circuit composed of inductance L and resistance R. Both L and R are functions of frequency. When the wire passes through the ferrite core, the inductive impedance formed increases in form with the increase of frequency, but the mechanism is completely different at different frequencies.
Different ferrite suppression components have different optimal suppression frequency ranges. Generally, the higher the permeability, the lower the frequency of suppression. In addition, the larger the volume of ferrite, the better the suppression effect. When the volume is constant, the long and thin shape has better suppression effect than the short and thick shape, and the smaller the inner diameter, the better the suppression effect. However, in the presence of DC or AC bias current, there is still the problem of ferrite saturation. The larger the cross-section of the suppression element, the less likely to be saturated and the greater the bias current that can be tolerated.
When the EMI absorption magnetic ring/magnetic bead suppresses differential mode interference, the current value passing through it is proportional to its volume. The imbalance of the two causes saturation and reduces the performance of the component; when suppressing common mode interference, connect the two wires of the power supply (positive and negative) Passing through a magnetic ring at the same time, the effective signal is a differential mode signal, and the EMI absorption magnetic ring/magnetic bead has no effect on it, but for the common mode signal, it will show a larger inductance. Another better way to use the magnetic ring is to make the wires of the magnetic ring that pass through it repeatedly to increase the inductance. According to its suppression principle of electromagnetic interference, its suppression effect can be used reasonably.
Ferrite suppression components should be installed close to the source of interference. For the input/output circuit, it should be as close as possible to the entrance and exit of the shielding case. For the absorption filter composed of ferrite bead and magnetic beads, in addition to the use of lossy materials with high permeability, attention should also be paid to its application. Their resistance to high-frequency components in the circuit is about ten to several hundred Ω, so its role in high-impedance circuits is not obvious. On the contrary, in low-impedance circuits (such as power distribution, power supply or radio frequency circuits) Use will be very effective.
Because ferrite can attenuate higher frequencies while allowing lower frequencies to pass almost unimpeded, it has been widely used in EMI control. The magnetic ring/magnetic beads used for EMI absorption can be made into various shapes and widely used in various occasions. If it is on the PCB board, it can be added to the DC/DC module, data line, power line, etc. It absorbs high-frequency interference signals on the line where it is located, but it will not generate new poles and zeros in the system, and will not destroy the stability of the system.