The reason for using patch beads and chip inductors is whether to use patch beads or chip inductors, mainly because of their applications. Chip inductors are needed in a resonant circuit. The use of patch beads is the best choice for eliminating unnecessary EMI noise.
1., the magnetic bead unit is Ohm, rather than Hunter, this point should pay special attention to. Because the unit of magnetic beads is nominal according to the impedance it produces at a certain frequency, the unit of resistance is also ohm. Magnetic beads on the DataSheet generally provide frequency and impedance characteristics of the curve, generally to 100MHz as standard, such as 1000R 100MHz, meaning that when the 100MHz frequency, magnetic beads impedance equivalent to 600 ohms.
2. the ordinary filter is made up of lossless reactance element. Its function is to reflect the stopband frequency back to the signal source in the circuit, so the filter is also called the reflection filter. When the reflected filter does not match the impedance of the signal source, a portion of the energy is reflected back to the signal source, resulting in an increase in the interference level. In order to solve this problem, the ferrite magnetic ring or magnetic bead sleeve can be used on the input line of the filter. The eddy current loss of the high frequency signal can be converted into heat loss by using the ring or magnetic beads. Therefore, magnetic rings and magnetic beads actually absorb high frequency components, so they are sometimes referred to as absorbing filters.
Different ferrite inhibitory elements have different optimum inhibitory frequency ranges. Generally, the higher the permeability is, the lower the frequency of inhibition is. In addition, the larger the volume of ferrite, the better the inhibitory effect. I love the program online some major bull research found that: when the volume is fixed, the long and thin shape than short and thick suppression effect is good, the smaller the diameter, the better the suppression effect. But in a DC or AC bias conditions, there exists the problem of ferrite saturation, the greater the inhibitory element cross section, the more easily saturated, can withstand greater drift. EMI absorption magnetic beads / suppressdifferential mode interference, through which the current value is proportional to its volume, the two disorders caused by saturation, reducing the component performance; suppression of common mode interference, the power of the two lines (positive and negative) through a ring at the same time, the effective signal to differential signal, EMI absorption magnetic beads / no influence on it, and for the common mode signal will show larger inductance. There is also a better way to use magnetic rings, which is to let the wires passing through the magnetic rings move repeatedly to increase inductance. According to the principle of electromagnetic interference suppression, it can be used reasonably.
Ferrite suppression devices should be installed near the source of interference. The input / output circuit shall be as close as possible to the inlet and outlet of the shield. The absorbing filter composed of ferrite, magnetic ring and magnetic bead should pay attention to its application besides the high permeability lossy material. Resistance in circuit of high frequency component of the show is about ten to several hundred, so its role in the high impedance circuit is not obvious, on the contrary, in low impedance circuit (such as power distribution, power supply or RF circuit) in use will be very effective.
Because ferrite can attenuate high frequency and let low frequency pass through almost unimpeded, it has been widely used in EMI control. The magnetic ring / bead used for EMI absorption can be made into various shapes and widely used in various occasions. Such as in the PCB board, can be added to the DC/DC module, data lines, power lines and so on. It absorbs the high frequency interference signal on the line, but does not generate new zeros and poles in the system, and does not destroy the stability of the system. The utility model can be used in conjunction with the power filter to improve the performance of the high-frequency end of the filter and improve the filtering characteristics in the system.
Magnetic beads are used to suppress high frequency noise and spike interference on signal lines, power lines, and to absorb electrostatic pulses.
The bead is used 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, used 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 noise, RF energy is AC sine wave components in the DC transmission level of DC component is useful signal, and the electromagnetic energy is useless RF RF interference along the transmission line and radiation (EMI). To eliminate these unnecessary signal energies, use patch beads as the role of 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 patch magnetic beads.
The patch magnetic beads consist of soft ferrite materials and form a monolithic structure with high volume resistivity. Eddy current loss is inversely proportional to the resistivity of ferrite material. Eddy current losses are proportional to the square of the signal frequency. The advantage of using patch beads: miniaturization and lightweight, high impedance in the RF noise frequency range, eliminating EMI in the transmission line. The closed 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 useful 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 several MHz to several hundred MHz.
In order to select magnetic beads correctly, the electronic component technology network is given and some core suggestions are given:
What is the frequency range of the non required signal?;
Who is the noise source?;
Is there space to place magnetic beads on the PCB board?;
How much noise attenuation is required?;
What are the environmental conditions (temperature, DC voltage, structural strength)?;
What is the impedance of the circuit and the load?;
The first three can be judged by observing 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 ZR22 PI fL () 2+:=fL. Through this curve, a magnetic bead model with a maximum impedance in the frequency range of the desired attenuation noise is selected, and the bead size as low as possible at low frequency and under DC is attenuated. The magnetic impedance of the bead is affected by the excessive DC voltage. Otherwise, if the temperature rise is too high, or the external magnetic field is too large, the impedance of the magnetic bead will be adversely affected. You can also pick it up at the Shenzhen electronic show. The reason for using patch beads and chip inductors is whether to use patch beads or chip inductors, mainly because of their applications. Chip inductors are needed in a resonant circuit. The use of patch beads is the best choice for eliminating unnecessary EMI noise.
Patch magnet bead and patch inductor applications:
Inductance: radio frequency (RF) and wireless communication, information technology equipment, radar detector, automobile, cellular phones, pagers, audio equipment, PDAs (personal digital assistant), wireless remote control system and low voltage power supply module etc..
SMD beads: clock circuit, analog circuit and digital circuit filter, I/O input / output internal connector (such as serial port, parallel port, keyboard, mouse, telecommunication, local area network), radio frequency (RF) between the circuit and the logic device is susceptible to interference, power supply circuit to filter the high-frequency conducted interference, computer. Machine, video recorder (VCRS), EMI noise suppression system and mobile phone in tv.
