The difference between magnetic beads and inductors and their functions and uses

The difference between magnetic beads and inductors and their functions and uses

Inductors are mostly used in power supply filter circuits, while magnetic beads are mostly used in signal circuits. For EMC countermeasures, magnetic beads are mainly used to suppress electromagnetic radiation interference, while inductors are used in this regard to focus on suppressing conducted interference. Both can be used to deal with EMC and EMI problems. Magnetic beads are used to absorb ultra-high frequency signals. Some RF circuits, PLLs, oscillation circuits, and ultra-high frequency memory circuits (DDR SDRAM, RAMBUS, etc.) all require magnetic beads to be added to the power input part, while inductors are a kind of energy storage element, used in LC oscillation circuits, medium and low frequency filter circuits, etc., and their application frequency range rarely exceeds 50MHZ. Inductors are generally used for ground connections, inductors are also used for power connections, and magnetic beads are used for signal lines?
But in fact, magnetic beads should also be able to achieve the purpose of absorbing high-frequency interference? Moreover, inductors can no longer play the role of inductors after high-frequency resonance. First, it is necessary to understand the two paths of EMI, namely: radiation and conduction. Different paths use different suppression methods. The former uses magnetic beads, and the latter uses inductors. For the IO part of the wrench, can we use an inductor to isolate the IO part from the wrench ground for EMC purposes? For example, isolating the USB ground and the wrench ground with a 10uH inductor prevents plug-in noise from interfering with the ground plane? Inductors are generally used for circuit matching and signal quality control. Magnetic beads are used where the analog ground and digital ground are combined. Magnetic beads are used where the analog ground and digital ground are combined. How big the magnetic beads between the digital ground and the analog ground are, and the size of the magnetic beads (to be precise, the characteristic curve of the magnetic beads) depends on the frequency of the interference wave you need the magnetic beads to absorb. Why are the units of magnetic beads and resistors the same? ? They are all ohms!! Magnetic beads are used to block high frequencies. They have low resistance to DC and high resistance to high frequencies. Isn't it easy to understand? For example, 1000R@100Mhz means that there is a resistance of 1000 ohms for a 100M frequency signal, because the unit of the magnetic bead is nominal according to the impedance it generates at a certain frequency, and the unit of impedance is also ohms. The datasheet of the magnetic bead usually includes a characteristic curve of frequency and impedance. Generally, 100MHz is used as the standard. For example, 2012B601 means that the impedance of the magnetic bead is 600 ohms at 100MHz.

The magnetic bead is composed of an oxygen magnet, and the inductor is composed of a magnetic core and a coil. The magnetic bead converts the AC signal into heat energy, and the inductor stores the AC and releases it slowly.
The magnetic bead has a greater blocking effect on high-frequency signals. The general specifications are 100 ohms/100mMHZ. Its resistance is much smaller than that of the inductor at low frequencies. The equivalent resistance of the inductor can be obtained by Z=2X3.14xf.

Ferrite beads are a kind of anti-interference component that is currently developing rapidly. They are cheap,
easy to use, and have a significant effect in filtering high-frequency noise.

In the circuit, as long as the wire passes through it (the ones I use are all like ordinary resistors, the wires have been passed through and
glued, and there are also surface mount forms, but they are rarely sold). When the current in the wire passes through, the ferrite
has almost no impedance to the low-frequency current, but it will have a greater attenuation effect on the higher-frequency current.
The high-frequency current is dissipated in the form of heat. Its equivalent circuit is an inductor and a resistor in series, and
the values ​​of the two components are proportional to the length of the magnetic bead.

There are many types of magnetic beads. Manufacturers should provide technical indicators, especially
the curve of the impedance and frequency relationship of the magnetic beads.

Some magnetic beads have multiple holes. Passing a wire through them can increase the impedance of the component (the square of the number of times the magnetic beads are passed through).
However, the increased noise suppression ability at high frequencies may not be as much as expected, and
it would be better to use more magnetic beads in series.

Ferrite is a magnetic material. It will produce magnetic saturation due to excessive current passing through it, and the magnetic permeability will drop sharply. For large current
filtering, magnetic beads specially designed in structure should be used, and attention should be paid to its heat dissipation measures.

Ferrite beads can not only be used to filter high-frequency noise in power supply circuits (can be used for DC and AC output),
but can also be widely used in other circuits, and their size can be made very small. Especially in digital circuits, since
pulse signals contain high-frequency high-order harmonics, which are also the main source of high-frequency radiation in circuits,
magnetic beads can be used in this occasion.

Ferrite beads are also widely used in noise filtering of signal cables.

Taking HH-1H3216-500, which is commonly used in power supply filtering, as an example, the meanings of the various fields of its model are as follows:
HH is one of its series, mainly used for power supply filtering, and the HB series is used for signal lines;
1 means that a component encapsulates a magnetic bead, and if it is 4, four beads are encapsulated side by side;
H represents the constituent materials, H, C, and M are medium frequency applications (50-200MHz),
T is low frequency applications (<50MHz), and S is high frequency applications (>200MHz);
3216 is the package size, 3.2mm long and 1.6mm wide, that is, 1206 package;
500 is the impedance (generally at 100MHz), 50 ohm.

There are three main parameters of its products:
Impedance [Z]@100MHz (ohm): Typical 50, Minimum 37;
DC Resistance (m ohm): Maximum 20;
Rated Current (mA): 2500.

Magnetic beads have high resistivity and permeability. They are equivalent to resistors and inductors in series, but both resistance and inductance values ​​vary with frequency. They have better high-frequency filtering characteristics than ordinary inductors. They are resistive at high frequencies, so they can maintain high impedance in a fairly wide frequency range, thereby improving the FM filtering effect.

Magnetic beads are mainly used for high-frequency isolation and suppression of differential mode noise. Magnetic
beads have high resistivity and permeability. They are equivalent to resistors and inductors in series, but both resistance and inductance values ​​vary with frequency. They have better high-frequency filtering characteristics than ordinary inductors. They are resistive at high frequencies, so they can maintain high impedance in a fairly wide frequency range, thereby improving the FM filtering effect.
Inductors can be used as power supply filters. The circuit symbol of the magnetic bead is the inductor, but the model number shows that the magnetic bead is used. In terms of circuit function, the magnetic bead and the inductor are based on the same principle, but the frequency characteristics are different.
The magnetic bead is composed of an oxygen magnet, and the inductor is composed of a magnetic core and a coil. The magnetic bead converts the AC signal into heat energy, and the inductor stores the AC and releases it slowly.
The magnetic bead has a greater blocking effect on high-frequency signals. The general specifications are 100 ohms/100mMHZ. Its resistance is much smaller than that of the inductor at low frequencies.
Ferrite beads (Ferrite Bead) are a kind of anti-interference component that is currently developing rapidly. They are cheap, easy to use, and have a significant effect in filtering high-frequency noise.
In the circuit, as long as the wire passes through it (I use those that look like ordinary resistors, the wires have been passed through and glued, and there are also surface mount forms, but they are rarely sold). When the current passes through the wire, the ferrite has almost no impedance to the low-frequency current, but it will have a greater attenuation effect on the higher-frequency current. High-frequency current is dissipated in the form of heat, and its equivalent circuit is an inductor and a resistor in series, and the values ​​of the two components are proportional to the length of the magnetic bead. There are many types of magnetic beads, and the manufacturer should provide technical indicators, especially the curve of the impedance and frequency relationship of the magnetic beads.
Some magnetic beads have multiple holes, and passing a wire through them can increase the component impedance (the square of the number of times the magnetic beads are passed through), but the increased noise suppression ability at high frequencies may not be as much as expected, and it would be better to connect more magnetic beads in series.
Ferrite is a magnetic material, which will produce magnetic saturation due to excessive current passing through, and the magnetic permeability will drop sharply. High current filtering should use magnetic beads specially designed in structure, and attention should also be paid to its heat dissipation measures.
Ferrite beads can not only be used to filter high-frequency noise in power supply circuits (can be used for DC and AC output), but can also be widely used in other circuits, and their size can be made very small. Especially in digital circuits, since pulse signals contain high-frequency high-order harmonics, which are also the main source of high-frequency radiation in circuits, magnetic beads can play a role in this occasion.
Ferrite beads are also widely used in noise filtering of signal cables.
Taking HH-1H3216-500, which is commonly used for power supply filtering, as an example, the meanings of the various fields of its model are as follows:
HH is a series, mainly used for power supply filtering, and the HB series is used for signal lines;
1 means that a component encapsulates a magnetic bead, and if it is 4, four beads are encapsulated side by side;
H represents the constituent material, H, C, and M are medium frequency applications (50-200MHz),
T is low frequency application (50MHz), and S is high frequency application (200MHz);
3216 package size, 3.2mm long, 1.6mm wide, i.e. 1206 package;
500 impedance (generally at 100MHz), 50 ohm.
Its product parameters mainly include three items:
impedance [Z]@100MHz (ohm): Typical 50, Minimum 37;
DC resistance (m ohm): Maximum 20;
Rated current (mA): 2500.
What magnetic beads are answered?
Principle of magnetic beads
The main raw material of magnetic beads is ferrite. Ferrite is a ferrimagnetic material with a cubic lattice structure. 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. A type of magnetic core commonly used in electromagnetic interference filters is ferrite material. Many manufacturers provide ferrite materials specifically for electromagnetic interference suppression. The characteristics of this material are that the high-frequency loss is very large and it has a very high magnetic permeability. It can minimize the capacitance between the coil windings of the inductor under high-frequency and high-resistance conditions. For ferrites used to suppress electromagnetic interference, the most important performance parameters are magnetic permeability μ and saturation flux density Bs. Magnetic permeability μ can be expressed as a complex number, the real part constitutes the inductance, and the imaginary part represents the loss, which increases with the increase of frequency. Therefore, its equivalent circuit is a series circuit composed of inductance L and resistance R, and L and R are both functions of frequency. When the wire passes through this ferrite core, the inductor impedance formed increases in form with the increase of frequency, but its mechanism is completely different at different frequencies.
In the low frequency band, the impedance is composed of the inductive reactance of the inductor. At low frequencies, R is very small, and the magnetic permeability of the magnetic core is high, so the inductance is large, and L plays a major role. The electromagnetic interference is reflected and suppressed, and the loss of the magnetic core is small at this time. The entire device is an inductor with low loss and high Q characteristics. This inductor is easy to cause resonance. Therefore, in the low frequency band, sometimes the interference may be enhanced after using ferrite beads.
In the high frequency band, the impedance is composed of the resistance component. As the frequency increases, the magnetic permeability of the magnetic core decreases, resulting in a decrease in the inductance of the inductor and a decrease in the inductive reactance component. However, at this time, the loss of the magnetic core increases, and the resistance component increases, resulting in an increase in the total impedance. When the high-frequency signal passes through the ferrite, the electromagnetic interference is absorbed and converted into heat energy and dissipated.
Ferrite suppression components are widely used in printed circuit boards, power lines, and data lines. If a ferrite suppression component is added to the power line inlet of the printed circuit board, high-frequency interference can be filtered out. Ferrite magnetic rings or beads are specially used to suppress high-frequency interference and spike interference on signal lines and power lines. It also has the ability to absorb electrostatic discharge pulse interference.
The values ​​of the two components are proportional to the length of the magnetic bead, and the length of the magnetic bead has a significant effect on the suppression effect. The longer the magnetic bead is, the better the suppression effect is.
The difference between magnetic beads and inductors
Inductors are energy storage components, while magnetic beads are energy conversion (consumption) devices. Inductors are mostly used in power supply filter circuits, focusing on suppressing conducted interference; magnetic beads are mostly used in signal circuits, mainly for EMI. Magnetic beads are used to absorb ultra-high frequency signals. Some RF circuits, PLLs, oscillation circuits, and ultra-high frequency memory circuits (DDR, SDRAM , RAMBUS, etc.) all require magnetic beads to be added to the power input part, while inductors are energy storage components used in LC oscillation circuits, medium and low frequency filter circuits, etc., and their application frequency range rarely exceeds 50MHz.

1. Chip inductors: Inductive components and EMI filter components are widely used in PCB circuits of electronic devices. These components include chip inductors and chip magnetic beads. The following describes the characteristics of these two devices and analyzes their common applications and special applications. The advantage of surface mount components is that the package size is small and can meet the requirements of actual space. Except for the difference in impedance value, current carrying capacity and other similar physical characteristics, the other performance characteristics of through-hole connectors and surface mount devices are basically the same. In situations where chip inductors are needed, the inductors are required to achieve the following two basic functions: circuit resonance and choke reactance. Resonant circuits include resonance generating circuits, oscillation circuits, clock circuits, pulse circuits, waveform generating circuits, etc. Resonant circuits also include high-Q bandpass filter circuits. In order for the circuit to resonate, both capacitance and inductance must exist in the circuit. There is parasitic capacitance at both ends of the inductor, which is caused by the ferrite body between the two electrodes of the device being equivalent to the capacitor medium. In the resonant circuit, the inductor must have high Q, narrow inductance deviation, and stable temperature coefficient to achieve the requirements of narrow band and low frequency temperature drift of the resonant circuit. High-Q circuits have sharp resonant peaks. Narrow inductance bias ensures that the resonant frequency deviation is as small as possible. Stable temperature coefficient ensures that the resonant frequency has stable temperature change characteristics. The difference between standard radial lead inductors and axial lead inductors and chip inductors is only in the different packaging. The inductor structure includes a coil wound on a dielectric material (usually an alumina ceramic material), or an air-core coil and a coil wound on a ferromagnetic material. In power applications, when used as a choke, the main parameters of the inductor are DC resistance (DCR), rated current, and low Q value. When used as a filter, a wide bandwidth characteristic is desired, so the high Q characteristic of the inductor is not required. Low DCR can ensure the minimum voltage drop. DCR is defined as the DC resistance of the component without an AC signal.
2. Chip beads: The function of chip beads is mainly to eliminate RF noise existing in the transmission line structure ( PCB circuit ). RF energy is an AC sine wave component superimposed on the DC transmission level. The DC component is the desired useful signal, while the RF energy is useless electromagnetic interference transmitted and radiated along the line (EMI). To eliminate these unwanted signal energies, chip beads are used to play the role of high-frequency resistors (attenuators). The device allows DC signals to pass through and filters out AC signals. Usually the high-frequency signal is above 30MHz, however, low-frequency signals will also be affected by chip beads.
Chip beads are made of soft ferrite materials, forming a monolithic 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 chip beads:
miniaturization and lightweight. High impedance in the RF noise frequency range, eliminating electromagnetic interference in the transmission line. Closed magnetic circuit structure, better eliminate signal crosstalk. Excellent magnetic shielding structure. Reduce DC resistance to avoid excessive attenuation of useful signals.

Significant high-frequency characteristics and impedance characteristics (better elimination of RF energy). Eliminate parasitic oscillations in high-frequency amplifier circuits. Effectively work in the frequency range of several MHz to hundreds of MHz. To correctly select magnetic beads, you must pay attention to the following points: What is the frequency range of the unwanted signal. Who is the noise source. How much noise attenuation is required. What are the environmental conditions (temperature, DC voltage, structural strength). What is the circuit and load impedance. Is there space to place the magnetic beads on the PCB board. The first three can be judged by observing the impedance frequency curve provided by the manufacturer. In the impedance curve, three curves are very important, namely resistance, inductance and total impedance. The total impedance is described by ZR22πfL()2+:=fL. The typical impedance curve can be found in the DATASHEET of the magnetic bead.
Through this curve, select the ferrite bead model with the maximum impedance in the frequency range where you want to attenuate noise and the smallest signal attenuation at low frequency and DC. The impedance characteristics of chip ferrite beads will be affected under excessive DC voltage. In addition, if the operating temperature rise is too high or the external magnetic field is too large, the impedance of the ferrite beads will be adversely affected.
Reasons for using chip ferrite beads and chip inductors: Whether to use chip ferrite beads or chip inductors depends mainly on the application. Chip inductors are required in resonant circuits. When it is necessary to eliminate unwanted EMI noise, using chip ferrite beads is the best choice. Applications of chip ferrite beads and chip inductors: Chip inductors: radio frequency (RF) and wireless communications, information technology equipment, radar detectors, automotive electronics, cellular phones, pagers, audio equipment, PDAs (personal digital assistants), wireless remote control systems, and low-voltage power supply modules. Chip ferrite 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 telecommunication, local area network), between radio frequency (RF) circuit and logic devices susceptible to interference, filtering high-frequency conducted interference in power supply circuit, computer, printer, video recorder (VCRS), TV system and EMI noise suppression in mobile phone.
Selection of ferrite beads

1. The unit of ferrite beads is ohm, not hunter, which should be paid special attention to. Because the unit of ferrite beads is nominal according to the impedance it produces at a certain frequency, the unit of impedance is also ohm. The DATASHEET of ferrite beads generally provides a characteristic curve of frequency and impedance, generally based on 100MHz, such as 1000R@100MHz, which means that the impedance of the ferrite beads is equivalent to 600 ohms at a frequency of 100MHz.

2. Ordinary filters are composed of lossless reactance elements. Its function in the line is to reflect the stopband frequency back to the signal source, so this type of filter is also called a reflection filter. When the reflection filter does not match the signal source impedance, part of the energy will be reflected back to the signal source, causing an increase in the interference level. To solve this problem, ferrite magnetic rings or magnetic beads can be used on the incoming line of the filter, and the eddy current loss of the high-frequency signal by the ferrite rings or magnetic beads can be used to convert the high-frequency component into heat loss. Therefore, the magnetic rings and magnetic beads actually absorb the high-frequency components, so they are sometimes called absorption filters.
Different ferrite suppression elements have different optimal suppression frequency ranges. Generally, the higher the magnetic permeability, the lower the suppression frequency. In addition, the larger the volume of the ferrite, the better the suppression effect. When the volume is constant, the long and thin shape has a better suppression effect than the short and thick one, and the smaller the inner diameter, the better the suppression effect. However, in the case 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 it is to saturate, and the greater the bias current it can withstand.
When the EMI absorption magnetic ring/bead suppresses differential mode interference, the current value passing through it is proportional to its volume. The imbalance between the two causes saturation and reduces the performance of the component. When suppressing common mode interference, the two wires (positive and negative) of the power supply pass through a magnetic ring at the same time. The effective signal is a differential mode signal. The EMI absorption magnetic ring/bead has no effect on it, but it will show a large inductance for the common mode signal. Another good way to use the magnetic ring is to let the wire passing through the magnetic ring be repeatedly wound several times to increase the inductance. According to its principle of suppressing electromagnetic interference, its suppression effect can be reasonably used.
Ferrite suppression components should be installed close to the interference source. For input/output circuits, they should be as close as possible to the entrance and exit of the shielding shell. For the absorption filter composed of ferrite magnetic rings and magnetic beads, in addition to selecting lossy materials with high magnetic permeability, it is also necessary to pay attention to its application occasion. The resistance they present to high-frequency components in the line is about ten to several hundred Ω, so its effect in high-impedance circuits is not obvious. On the contrary, it will be very effective in low-impedance circuits (such as power distribution, power supply or radio frequency circuits).
Conclusion
Ferrite is widely used in EMI control because it can attenuate higher frequencies while allowing lower frequencies to pass almost unimpeded. Magnetic rings/beads used for EMI absorption can be made into various shapes and are widely used in various occasions. For example, on PCB boards, they can be added to DC/DC modules, data lines, power lines, etc. It absorbs high-frequency interference signals on the line, but does not generate new zeros and poles in the system, and does not destroy the stability of the system. It can be used in conjunction with the power supply filter to well supplement the shortcomings of the filter's high-frequency performance and improve the filtering characteristics in the system.