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Murata is always confused with magnetic beads? This article helps you solve this problem.
2018-11-19
 
I believe that you are already familiar with the concept and basic principles of inductance, and the editor will not elaborate on them here. Today's leading role is the magnetic attraction of a good brother, magnetic bead. Inductors and magnetic beads, these two devices play an irreplaceable role in electronic design. This article will make a comprehensive comparison of inductance and magnetic beads to help you understand the similarities and differences between them.


Application difference in circuit


As we all know, inductors are energy storage elements, while magnetic beads consume devices. Different functions mean that the application fields of both are different. Inductance is mostly used in power filter circuit, magnetic beads are mostly used in signal circuit, and magnetic beads used in EMC are mainly used to suppress electromagnetic radiation interference, while inductance is mainly used to suppress conductive interference.


It is worth noting that although the functions in the circuit are different, the beads and inductors can be used to deal with electromagnetic interference. Magnetic beads are used to absorb ultra-high frequency signals, such as some RF circuits, PLL, oscillation circuits, including ultra-high frequency memory circuits (DDR SDRAM, RAMBUS, etc.) all need to add magnetic beads in the input part of the power supply, while inductance is an energy storage element, which is used in LC oscillation circuits, filter circuits at medium and low frequencies, and its application frequency range is seldom more than 50 MHZ. . The connection of the earth usually uses inductance, and the connection between the power source is also inductor, and magnetic beads are applied to the signal line.


In the case of high frequency resonance, inductance is not as good as magnetic beads. Magnetic beads can also absorb high-frequency interference, and inductance has lost its original role in this case. To understand why inductors fail, it is necessary to understand two ways of EMI: radiation and transmission, and different ways of suppression. The former uses magnetic beads and the latter uses inductors. For the IO part of the wrench, EMC can be used to isolate the IO part from the ground of the wrench. For example, the ground of USB and the ground of wrench are isolated from the inductance of 10uH. The ground surface can be prevented from jamming by jamming.


Magnetic beads are used to simulate the combination of digitally and digitally. How big is the magnetic bead used between digital and analog earth? The size of the magnetic bead (exactly the characteristic curve of the magnetic bead) depends on the frequency of the interference wave absorbed by the magnetic bead. Why is the unit and resistance of the magnetic bead the same? The magnetic bead is high frequency resistance, low DC resistance and high frequency resistance, so it is easy to understand. For example, 1000R@100Mhz means 1000 ohms resistance to 100M frequency signal, because the unit of magnetic beads is nominated according to the impedance it produces at a certain frequency, and the unit of impedance is also ohms. The magnetic bead datasheet usually has a characteristic curve of frequency and impedance. Generally, the standard is 100MHz, such as 2012 B601, which means that the Impedance of magnetic beads is 600 ohms at 100MHz.


In many products, the two places of the switch are connected by capacitors, so why not use inductance? If magnetic beads or direct connections are used, unexpected levels such as human static electricity will easily enter the ground of the switch, so that the switch will not work properly. But if they are disconnected, the sparks between the two places can cause fire when they are struck by lightning or other high pressures. Capacitors are added to avoid this situation.


The ground of the switch is to eliminate harmonics through the capacitance between the two ground. Like a transformer with high impedance, it has a harmonic elimination circuit. Ferrite material is ferro-magnesium alloy or ferro-nickel alloy, which has high permeability and can minimize the capacitance between coils of inductors at high frequency and high resistance. Ferrite materials are usually used at high frequencies, because their main path inductance characteristics at low frequencies make the loss on the line very small. At high frequencies, they mainly exhibit reactance characteristic ratio and vary with frequency. In practical applications, ferrite material is used as a high frequency attenuator for RF circuits. In fact, ferrite is better equivalent to the parallel connection of resistance and inductance. The resistance is short-circuited by inductance at low frequency, and the inductance impedance becomes quite high at high frequency, so that all the current passes through the resistance. Ferrite is a consuming device on which high frequency energy is converted into heat energy, which is determined by its resistance characteristics.


The difference between structure and actual production


From the exterior structure, we can see the difference between them. We can separate inductors and magnetic beads through the number of coils. The coil with more than one turn is called inductance coil, and the coil with less than one turn is called magnetic bead. The use is determined by the required inductance.


In some products, inductance is used instead of the filtering effect of magnetic beads. In fact, this is feasible. The circuit symbol of magnetic beads is inductance, but it can be seen from the model that magnetic beads are used. On the function of the circuit, the magnetic bead and inductance are the same principle, but the frequency characteristics are different.


This article begins with an in-depth analysis of the principle, helps you to analyze the similarities and differences between inductance and magnetic beads, and finally provides a method to distinguish inductance from magnetic beads in terms of structure and practical application. I hope all of you will be able to quickly identify inductors and magnetic beads after reading this article.
 
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