PCB News - The selection of magnetic beads in PCB circuit design

The selection of magnetic beads in PCB circuit design

The unit of the magnetic beads is ohms, not Hunter, this should be paid special attention to. Because the unit of the magnetic bead is nominally based on the impedance it generates at a certain frequency, the unit of impedance is also ohms. The DATASHEET of the magnetic beads generally provides frequency and impedance characteristic curves. Generally, 100MHz is the standard, which means that the impedance of the magnetic beads is equivalent to 600 ohms at a frequency of 100MHz.

Ordinary filters are composed of lossless reactive components, and their role 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 impedance of the signal source, a part of the energy will be reflected back to the signal source, resulting in an increase in the interference level. In order to solve this problem, a ferrite magnetic ring or magnetic bead sleeve can be used on the incoming line of the filter to use the eddy current loss of the ring or magnetic bead to the high-frequency signal to convert the high-frequency component into heat loss. Therefore, the magnetic ring and the magnetic beads actually absorb high-frequency components, so they are sometimes called absorption filters.

Different ferrite suppression components have different optimal suppression frequency ranges. Generally, the higher the permeability, the lower the frequency of suppression. In addition, the larger the volume of ferrite, the better the suppression effect. When the volume is constant, the long and thin shape has better suppression effect than the short and thick shape, and the smaller the inner diameter, the better the suppression effect. However, in the presence of DC or AC bias current, there is still the problem of ferrite saturation. The larger the cross section of the suppression component, the less saturated it is, and the greater the bias current that can be tolerated. When the EMI absorption magnetic ring/magnetic bead suppresses the differential mode interference, the current value passing through it is proportional to its volume. The imbalance of the two causes saturation and reduces the performance of the component; when suppressing common mode interference, connect the two wires of the power supply (positive and negative) Passing through a magnetic ring at the same time, the effective signal is a differential mode signal, and the EMI absorption magnetic ring/magnetic bead has no effect on it, but for the common mode signal, it will show a larger inductance. Another better way to use the magnetic ring is to make the wires of the magnetic ring that pass through it repeatedly to increase the inductance. According to its suppression principle of electromagnetic interference, its suppression effect can be used reasonably.

The above is an introduction to the selection of magnetic beads in PCB circuit design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.