磁珠（Magnetic beads）
Magnetic beads are ud to suppress high frequency noi and spike interference on signal lines, power lines, and to absorb electrostatic puls.
The bead is ud to absorb the UHF signal, like PLL, RF circuit, oscillator circuit, memory circuit with ultra high frequency (DDR, SDRAM, RAMBUS etc.) are required in the power input part and magnetic beads, and the inductance is an energy storage element, ud in the LC in the low frequency oscillation circuit, filter circuit and its application the frequency range is less than 50MHZ.
The main function is to eliminate the magnetic beads in transmission line structure (circuit) RF noi, RF energy is AC sine wave components in the DC transmission level of DC component is uful signal, and the electromagnetic energy is uless RF RF interference along the transmission line and radiation (EMI). To eliminate the unnecessary signal energies, the chip magnetic beads act as high frequency resistors (attenuators) that allow DC signals to pass through and filter out AC signals. Usually the high frequency signal is above 30MHz, however, the low-frequency signal is also affected by the chip magnetic beads.
The chip magnetic beads consist of soft ferrite materials, and form a monolithic structure with high volu
me resistivity. Eddy current loss is inverly proportional to the resistivity of ferrite material. Eddy current loss are proportional to the square of the signal frequency. The advantage of using chip beads: miniaturization and lightweight, high impedance in the
RF noi frequency range, eliminating EMI in the transmission line. The clod magnetic circuit structure can better eliminate the winding of the signal. Excellent magnetic shielding structure. Reduce DC resistance so as not to produce excessive attenuation of the uful signal.
Significant high frequency and impedance characteristics (better elimination of RF energy). Elimination of parasitic oscillations in high frequency amplification circuits. Effective work in a frequency range of veral MHz to veral hundred MHz.
To correctly lect magnetic beads, you must pay attention to the following points:
1, what is the frequency range of the non required signal?;
2, who is the source of noi?;
3, how much noi attenuation is required?;
4. What are the environmental conditions (temperature, DC voltage, structural strength)?;
5 、 what is the impedance of the circuit and load?;
6. Is there room for placing magnetic beads on the PCB board?;
The first three can be judged by obrving the impedance frequency curve provided by the manufacturer. In three the impedance curve curves are very important, namely, resistance,
reactance and impedance. The total impedance is described by means of ZR22 PI fL () 2+: =fL. Through this curve, a magnetic bead model with a maximum impedance in the frequency range of the desired attenuation noi is lected, and the bead size as low as possible at low frequency and under DC is attenuated. The magnetic impedance of the wafer is affected by the excessive DC voltage. Otherwi, if the temperature ri is too high, or the external magnetic field is too large, the impedance of the magnetic bead will be adverly affected. The reasons for the u of chip magnetic beads and chip inductors are chip magnetic beads or chip inductors, mainly in applications. Chip inductors are needed in resonant circuits. To eliminate unnecessary EMI noi, the u of chip beads is the best choice. Application of chip magnetic bead and chip inductor:
Chip inductors: radio frequency (RF) and wireless communications, information technology equipment, radar detectors, cars, cellular phones, pagers, audio equipment, PDAs (personal digital a
ssistant),
But the mechanism is quite different at different frequencies.
At low frequency, impedance by the inductive reactance of a low frequency when R is small, high permeability magnetic core inductance, so a large amount of L plays a major role, the electromagnetic interference is reflected and inhibited, and then the core loss is smaller, the entire device is a high inductance Q characteristic of low loss, and the inductance easily therefore cau resonance at low frequencies, sometimes using ferrite beads after interference enhancement phenomenon.
At high frequency, impedance by resistance elements, with the increa of frequency, magnetic permeability decrea, resulting in inductance inductance decreas, but decreas the inductive component, then the core loss is incread and the resistance component incread, which leads to the increa of total impedance, when the high frequency signal through the ferrite, the electromagnetic interference is absorbed and converted into form the heat dissipation.
Ferrite suppression devices are widely ud in printed circuit boards, power lines and data lines. If a ferrite suppression element is added at the entrance of the power line of the printed circuit board, hig
h frequency interference can be filtered out. Ferrite magnetic ring or magnetic beads are ud to suppress high frequency interference and peak interference on signal line and power line. It also has the ability to absorb static discharge pul interference. The size of the two components is proportional to the length of the magnetic beads, and the length of the magnetic beads has a significant influence on the inhibitory effect. The longer the magnetic bead length, the better the suppression effect.
Two, magnetic beads and inductance difference
Inductors are energy storage devices, and magnetic beads are energy conversion devices. Inductors are mostly ud in power filter circuits, with a focus on restraining conductive interference;
Magnetic beads are mostly ud in signal circuits. They are mainly ud in EMI. The bead is ud to absorb the UHF signal,
like PLL, RF circuit, oscillator circuit, memory circuit with ultra high frequency (DDR, SDRAM, RAMBUS etc.) are required in the power input part and magnetic beads, and the inductance is a storage element, ud in the LC in low frequency oscillation circuit, filter circuit, the frequency of application the range of little more than 50MHz.
1. piece inductance: in the electronic equipment PCB board circuit, will u the perceptual element and the EMI filter element in great quantities. The components include chip inductors and chip magnetic beads. The following describes the features of the two devices and analyzes their general applications and special applications. The advantage of SMT is its small package size and the ability to meet actual space requirements. In addition to impedance, current carrying capability, and other similar physical characteristics, the other performance characteristics of through-hole connectors and surface mount devices are esntially the same. In the ca of chip inductors, inductors are required to implement the following two basic functions: circuit resonance and choke reactance. The resonant circuit includes resonance generating circuit, oscillating circuit, clock circuit, pul circuit, waveform generating circuit, and so on. The resonant circuit also includes a high Q bandpass filter circuit. In order for the circuit to resonate, a capacitor and inductance must exist in the circuit simultaneously. There is a parasitic capacitance at the two ends of the inductor, which is due to the ferrite body between the two electrodes as a capacitive medium. In a resonant circuit, the inductor must have a high Q, a narrow inductance deviation, and a stable temperature coefficient to achieve a narrow band of the resonant circuit,
