What is a magnetic beads (Ferrite Bead is FB ))

What is magnetic beads?

Magnetic Beads have high resistivity and magnetic permeability, which is equivalent to a series of resistance and inductance, but the resistance value and Inductance Value Change with frequency. It has better high-frequency filtering characteristics than ordinary inductor, and presents resistance at high frequencies, so it can maintain a high impedance within a very wide frequency range, thus improving the FM filtering effect.
Inductance can be used as a power filter. The circuit symbol of the magnetic beads is inductance, but the model can be seen that the magnetic beads are used in the circuit function. The magnetic beads and the inductance are the same in principle, but the frequency characteristics are different.
Magnetic Beads are composed of oxygen magnets, and the inductance is composed of a magnetic core and a coil. The magnetic beads convert the AC signal into heat energy, and the inductance stores the AC and slowly releases it out.
Magnetic Beads have a major obstacle to high-frequency signals. Generally, the specification is 100 euro/100 mmhz, which has a much lower resistance than inductance at low frequencies.
Ferrite Bead is a fast-growing anti-interference component. It is cheap and easy to use, and has a significant effect on filtering out high-frequency noise.
In
As long as the wire passes through it in the circuit (I use the ordinary resistance, the wire has passed through and glued, there is also a form of surface mount, but rarely seen sold ). When the current in the wire passes through, ferrite is applied to low-frequency electricity.
The stream has almost no impedance, but it will have a great attenuation effect on high-frequency current. High-frequency current is emitted in the form of heat. Its Equivalent circuit is a series of inductance and a resistor. The values of both components are
. There are many types of magnetic beads. Manufacturers should provide technical indicators, especially the curve of the relationship between impedance and frequency of magnetic beads.
Some magnetic beads have multiple holes, and the component impedance (the square of the number of beads passed) can be increased when the wires pass through. However, the noise suppression capability increased at high frequencies cannot be as expected, however, it would be better to concatenate several magnetic beads.
Ferrite is a magnetic material that produces magnetic saturation due to excessive current, resulting in a sharp reduction in the magnetic conductivity. Large Current filtering should adopt specially designed magnetic beads, and pay attention to the heat dissipation measures.
Ferrite Magnetic Beads can be used not only in power supply circuit to filter out high-frequency noise (can be used for DC and AC output), but also widely used in other circuits, and their volume can be very small. Especially in digital circuits, pulse signals contain high-frequency harmonic waves, which are also the main source of high-frequency radiation. Therefore, magnetic beads can be used in such cases.
Ferrite Magnetic Beads are also widely used in Noise Filtering of signal cables.
Take the HH-1H3216-500 commonly used in power filter as an example, the meaning of each field of the model is:
HH is a series of it, mainly used for power filter, used for signal line is HB series;
1 indicates that a component encapsulates a magnetic bead. If it is 4, it encapsulates four beads side by side;
H indicates the composition of the substance. h, C, and m are used for intermediate frequency applications (50-200 MHz ),
T low frequency applications (50 MHz), s high frequency applications (200 MHz );
3216 encapsulation size, length 3.2mm, width 1.6mm, that is, 1206 encapsulation;
500 impedance (generally MHz), 50 ohm.
There are three main product parameters:
Impedance [Z] @ 100 MHz (OHM): Typical 50, minimum 37;
DC resistance (m ohm): maximum 20;
Rated current rated current (MA): 2500.
What magnetic beads have you answered?
Principles of magnetic beads

Magnetic
The main raw materials of beads are ferrite. Ferrite is a magnetic ferrous material with cubic lattice structure. Ferrite material is iron magnesium alloy or iron nickel alloy, its manufacturing process and mechanical properties are similar to ceramics, the color is gray black. Electricity
Ferrite is a kind of core that is often used in magnetic interference filters. Many manufacturers provide Ferrite Materials specially used for electromagnetic interference suppression. This material is characterized by high-frequency loss and high magnetic conductivity.
Rate, which can be the smallest capacitance generated between the coil winding of the inductor at high frequency and high impedance. The most important performance parameters for ferrite used to suppress electromagnetic interference are magnetic permeability μ and saturated magnetic flux density BS. Permeability
μ can be expressed as a complex number, and the real part constitutes an inductance. The imaginary part represents loss and increases with the increase of frequency. Therefore, the equivalent circuit is a series circuit consisting of inductance L and resistance R. Both L and R are frequency-effective.
Function. When a wire passes through this ferrite core, the inductance impedance increases with the increase of frequency, but its mechanism is completely different at different frequencies.
In the low frequency segment, the impedance
It is composed of Inductance inductance, low-frequency R is very small, and the magnetic permeability of the core is high. Therefore, the inductance is large, and the electromagnetic interference is restrained by reflection, in this case, the core loss is small, and the entire device is
Low-loss, high-Q-characterized inductor, which may cause resonance in the low-frequency segment, and sometimes may cause interference enhancement after the use of ferrite magnetic beads.
In the high-frequency band, the impedance is composed of resistance components. As the frequency increases, the magnetic permeability of the core decreases, resulting in reduced inductance and inductance. However, when the loss of the core increases, the resistance component increases, as a result, the total impedance increases. When high-frequency signals pass through ferrite, electromagnetic interference is absorbed and converted into heat energy for dissipation.
Ferrite suppression elements are widely used in printed circuit boards, power cords, and data cables. For example, if a ferrite suppression element is added to the power cord inlet of the printed board, high-frequency interference can be filtered out. Ferrite Magnetic rings or magnetic beads are used to suppress high-frequency interference and Spike interference on signal lines and power cables. They also have the ability to absorb electrostatic discharge pulse interference.
The size of the two elements is proportional to the length of the magnetic beads, and the length of the magnetic beads has a significant impact on the inhibition effect. The longer the length of the magnetic beads, the better the inhibition effect.
Difference between magnetic beads and inductor

Inductance is an energy storage component, while magnetic beads are an energy conversion (consumption) device. Inductance is mostly used in the power supply filter loop, focusing on the suppression of conductive interference; magnetic beads are mostly used in signal loop, mainly used in EMI. Magnetic Beads are used to absorb ultra-high frequency signals, such as RF circuits, PLL, oscillating circuits, and ultra-high frequency memory circuits (DDR, SDRAM ).
, Rambus, etc.) All need to be added to the power input part of the magnetic beads, and inductance is a storage component, used in LC oscillator circuit, medium and low frequency filter circuit, etc, the application frequency is rarely more than 50 MHz.

1. Chip Inductor: PCB on Electronic Devices
Board
A large number of Inductive Components and EMI filter elements are used in the circuit. These components include Chip Inductor and chip magnetic beads. The following describes the characteristics of these two devices and analyzes their common application scenarios and special application fields.
. The advantage of surface mount components is the small package size and the ability to meet the actual space requirements. In addition to impedance values, streaming capacity, and other similar physical properties, other properties of the through-hole connector and surface mount device
The features are basically the same. When chip inductor is needed, the inductor must implement the following two basic functions: circuit resonance and throttling. The resonant circuit includes a resonant circuit, an oscillating circuit, a clock circuit, and a pulse electric circuit.
Circuit, waveform circuit, and so on. The resonant circuit also includes a high-Q band-pass filter circuit. To make the circuit produce resonance, the capacitance and inductance must exist in the circuit at the same time. Parasitic Capacitance exists at both ends of the inductor, because
The ferrite body between two electrodes is equivalent to a capacitor medium. In a resonant circuit, the inductance must have high Q, narrow inductance deviation, and stable temperature coefficient to reach the narrow band and low frequency temperature of the resonant circuit.
Degree drift requirements. The high Q circuit has sharp resonance peaks. Narrow inductance offset ensures minimum deviation of resonant frequency. Stable Temperature Coefficient ensures stable temperature variation at the resonant frequency. Standard radial guide
The difference between inductive and axial inductance and chip inductance is that the encapsulation is different. Inductance structure includes medium material (usually alumina ceramic) winding, or hollow coil and magnetic material winding
Circle. In power applications, when used as a throttling ring, the main parameters of Inductance are DC resistance (DCR), rated current, and low Q. When used as a filter, you do not need to use the wide bandwidth.
High Q characteristics of inductance. Low DCR can minimize the voltage drop. DCR is defined as the DC resistance of a component without an AC signal.
2. Chip magnetic beads: the function of chip magnetic beads is mainly to eliminate the existing in the transmission line structure (PCB Circuit
)
RF noise, RF energy is the AC Sine Wave Composition superimposed on the DC transmission level, DC composition is a useful signal, while RF energy is useless electromagnetic interference transmitted along the line and radiation
(EMI ). To eliminate unnecessary signal energy, use a chip magnetic bead to act as a high-frequency resistor (the attenuation). The device allows the DC signal to pass through and filter out the AC signal. Usually the high-frequency signal is
Over 30 MHz, however, low-frequency signals may also be affected by chip magnetic beads.
The chip magnetic beads are composed of Soft Ferrite Materials and constitute a rock-shaped structure with high volume resistivity. Eddy Current Loss is inversely proportional to the resistivity of Ferrite Materials. Eddy Current Loss is proportional to the square of the signal frequency. Benefits of using a chip magnetic bead:
Small and lightweight. In RF
High impedance is available in the noise frequency range to eliminate electromagnetic interference in transmission lines. Close the magnetic circuit structure to better eliminate the string winding of signals. Excellent magnetic shielding structure. Reduce the DC resistance to avoid excessive attenuation of useful signals.

Significant high-frequency and impedance characteristics (better RF elimination)
Yes
Quantity ). Eliminate parasitic vibrations in high-frequency amplification circuits. It works effectively within the frequency range of several MHz to several hundred MHz. Pay attention to the following points for proper selection of magnetic beads:
The frequency range of the unwanted signal. Who is the noise source. How much noise is needed. What are the environmental conditions (temperature, DC voltage, structural strength ).
What is the circuit and load impedance. Whether there is space to place magnetic beads on the PCB. The first three pieces can be determined by observing the impedance frequency curve provided by the manufacturer. The three curves in the impedance curve are very important, namely resistance and sensing.
Resistance and total impedance. The total impedance is described by zr22 π Fl () 2 +: = FL. For a typical impedance curve, see Datasheet of the magnetic beads.
Through this curve, choose the magnetic beads with the highest impedance within the desired frequency range and the signal attenuation below low frequency and DC as small as possible. The impedance of the chip magnetic beads is affected when the DC voltage is too high. In addition, if the operating temperature is too high or the external magnetic field is too large, the impedance of the magnetic beads will be adversely affected.
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The reason for the use of chip magnetic beads and chip Inductance: whether the use of chip magnetic beads or chip inductance is mainly applied. Chip Inductor must be used in the resonant circuit. Chip magnetic beads are used to eliminate unwanted EMI noise.
Is the best choice. Chip magnetic beads and Chip Inductor applications:
Chip Inductor: RF and wireless communication, information technology equipment, radar detector, automotive electronics, cellular phone, pager, audio equipment, PDAs (Personal Digital Assistant ), wireless Remote Control System and low voltage
Power Supply Module. Chip magnetic beads: Clock generation circuit, filtering between analog circuit and digital circuit, I/O input/output internal connector (such as serial port, parallel port, keyboard, mouse, long distance Telecom, Local Area
Network), radio frequency (RF) circuit and susceptible to interference between the logic equipment, power supply circuit in the filtering of high frequency conduction interference, computers, printers, recorders (VCRs ), emi noise in television systems and mobile phones
Stop.
Selection of magnetic beads

1.
The unit of the magnetic beads is Ohm rather than Hunter. Pay special attention to this. Because the unit of the magnetic beads is nominal according to the impedance produced at a certain frequency, the unit of impedance is also ohm. Magnetic Beads
Datasheet generally provides characteristic curves of frequency and impedance, which are generally based on 100 MHz. For example, 1000r @ MHz, which means the magnetic
The impedance of the beads is equivalent to 600 ohm.

2.
A common filter is composed of a zero-loss impedance element. Its function in the line is to return the impedance band frequency back to the signal source. Therefore, this type of filter is also called a reflection filter. When the reflected filter does not match the signal source impedance,
Some of the energy will be reflected back to the signal source, resulting in increased interference levels. In order to solve this problem, ferrite magnetic ring or magnetic beads can be used in the inlet of the filter, and the eddy current loss of high-frequency signals can be caused by the zihuan or magnetic beads.
Converts high-frequency components into heat loss. Therefore, magnetic rings and magnetic beads are used to absorb high-frequency components. Therefore, they are also called absorption filters.
Different ferrite suppression elements have different optimal
Suppression frequency range. The higher the permeability, the lower the inhibition frequency. In addition, the larger the volume of ferrite, the better the inhibition effect. At the time of accumulation, the longer and finer shapes are better than the shorter and coarse shapes, and the smaller the inner diameter is
The better. However, in the case of DC or AC Partial flow, there is still the problem of ferrite saturation. The larger the cross section of the suppression element, the less saturated it is, and the larger the allowable partial flow.
Emi absorption magnetic ring
/When the magnetic beads suppress differential mode interference, the current value is proportional to its volume. The imbalance between the two causes saturation, reducing the performance of the component. When the common mode interference is suppressed, the two wires of the power supply (plus or minus) it passes through a magnetic ring at the same time, which is effective
The signal is a differential mode signal, and EMI absorption of magnetic ring/magnetic beads has no effect on it, while the common mode signal will show a large amount of electric sensing. Another good way to use the magnetic ring is to reverse the wire that passes through the magnetic ring.
Repeat a few times to increase the inductance. It can be used properly based on its suppression principle of electromagnetic interference.
Ferrite suppression elements should be installed near the interference source. For input/Input
The output circuit should be as close as possible to the inlet and outlet of the shielding shell. In addition to the consumable materials with high permeability, the absorption filter composed of the inner body magnetic ring and the magnetic beads should be used. They are high in line
The resistance presented by the frequency composition is about 10 to several hundred Ω, so it does not play a significant role in high impedance circuits. On the contrary, in low impedance circuits (such as power distribution, power supply, or RF circuits) is very effective.
Conclusion

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It is widely used in EMI control because ferrite can degrade at a high frequency and make the low frequency pass through without any obstacles. Magnetic rings/magnetic beads used for EMI absorption can be made into various shapes and are widely used in various
Occasion. For example, the PCB can be added to the DC/DC module, data cable, and power cord. It absorbs high-frequency interference signals on the road, but does not generate new zero-pole in the system, and does not damage the system stability.
. It is used in combination with the power filter, which can well supplement the low performance of the high-frequency end of the filter and improve the filtering characteristics in the system.