In PCB design, whether to use SMD magnetic beads or SMD inductors mainly focuses on the application scenario. Design pcb The design of printed circuit board is based on the circuit schematic diagram to realize the functions required by circuit designers. The design of printed circuit board mainly refers to layout design, and the layout of external connections needs to be considered. The resonant circuit needs patch inductance. When it is necessary to eliminate unnecessary EMI noise, the use of patch magnetic beads is the best choice. The unit of magnetic beads is ohm, not Hunter, so special attention should be paid to it. Because the unit of magnetic bead is marked according to its impedance at a certain frequency, the unit of impedance is also ohmic. The frequency and impedance characteristic curves of magnetic beads are generally provided on the data sheet of magnetic beads, generally based on 100 MHz, such as 1000R100 MHz, which means that the impedance of magnetic beads at 100 MHz is equivalent to 600 ohms. The commonly used filter is composed of lossless impedance components, whose function in the circuit is to reflect the stop-band frequency back to the signal source, so this filter is also called reflection filter. When the impedance of the reflection filter does not match the impedance of the signal source, part of the energy will be reflected back to the signal source, resulting in the improvement of the interference level. To solve this problem, a ferrite magnetic ring or a magnetic bead sleeve can be used on the input line of the filter, and the eddy current loss of the high-frequency signal caused by the magnetic ring or magnetic bead can be used to convert the high-frequency component into heat loss. Therefore, magnetic rings and beads actually absorb high-frequency components, so they are sometimes called absorption filters. Different ferrite suppression elements have different optimal suppression frequency ranges. Generally, the higher the permeability, the lower the inhibition frequency. In addition, the larger the ferrite volume, the better the corrosion inhibition effect. Some online studies have found that when the volume is constant, the long and thin shape is better than the short and thick shape, and the smaller the inner diameter, the better the inhibition effect. However, in the case of DC or AC bias, there is also the problem of ferrite saturation. The larger the cross section of the suppression element, the lower the saturation degree, and the greater the bias current it can bear. When EMI absorbs magnetic ring/magnetic bead to suppress differential mode interference, its current value is proportional to its volume, and the misalignment between them leads to saturation, which reduces the performance of components. When suppressing common-mode interference, the positive and negative lines of the power supply pass through the magnetic ring at the same time, and the effective signal is the differential mode signal. EMI absorbing magnetic ring/magnetic bead has no influence on magnetic ring/magnetic bead, but it will produce large inductance to common-mode signal. There is also a better way to use the magnetic ring, that is, the wire is repeatedly wound through the magnetic ring several times to increase the inductance. According to its electromagnetic interference suppression principle, its suppression effect can be reasonably utilized.
Ferrite suppression element should be installed near the interference source. Pcb Design The key to making a circuit board a “controllable impedance board” is to make the characteristic impedance of all circuits meet a specified value, usually between 25 ohms and 70 ohms. In multilayer circuit board, the key to good performance of transmission line is to keep its characteristic impedance constant in the whole line. As for the input/output circuit, it should be as close as possible to the inlet and outlet of the shielding case. For the absorption filter composed of ferrite magnetic ring and magnetic bead, we should not only choose the lossy material with high permeability, but also pay attention to its application. Their resistance to the high-frequency components in the circuit is about 10~ hundreds, and their role in high-impedance circuits is not obvious. On the contrary, they will be very effective in low-impedance circuits such as power distribution, power supply or radio frequency circuits.
Ferrite is widely used in electromagnetic interference (EMI) control, because it can attenuate higher frequencies and make low frequencies pass almost unimpeded. Magnetic rings/beads for electromagnetic interference absorption can be made into various shapes and widely used in various occasions. Such as PCB, can be added to DC/DC modules, data lines, power lines, etc.
