Are you all familiar with methods such as using filtering capacitors, common-mode inductors, and ferrite beads to eliminate electromagnetic interference 3

In fact, ferrite is better equivalent to the parallel connection of resistance and inductance. At low frequencies, the resistance is short circuited by the inductance, and at high frequencies, the impedance of the inductance becomes quite high, so that all current passes through the resistance. Ferrite is a consumable device that converts high-frequency energy into thermal energy, which is determined by its resistance characteristics. Ferrite magnetic beads have better high-frequency filtering characteristics compared to ordinary inductors.

Ferrite exhibits resistance at high frequencies, equivalent to an inductor with a very low quality factor, so it can maintain high impedance over a wide frequency range, thereby improving high-frequency filtering efficiency.

In the low frequency range, impedance is composed of the inductive reactance of inductance. At low frequencies, R is very small and the magnetic permeability of the magnetic core is high, resulting in a large inductance. L plays a major role, and electromagnetic interference is reflected and suppressed; And at this time, the loss of the magnetic core is relatively small, and the entire device is a low loss, high-Q characteristic inductor, which is prone to resonance. Therefore, in the low frequency range, sometimes iron may be used  diode

In the high frequency range, impedance is composed of resistance components. As the frequency increases, the magnetic permeability of the magnetic core decreases, resulting in a decrease in the inductance of the inductor and a decrease in the reactance component. However, at this point, the loss of the magnetic core increases, the resistance component increases, resulting in an increase in the total impedance. When high-frequency signals pass through ferrite, electromagnetic interference is absorbed and converted into thermal energy for dissipation. Ferrite suppression components are widely used in printed circuit boards, power lines, and data lines. If ferrite suppression components are added to the power line inlet end of the printed circuit board, high-frequency interference can be filtered out.

Ferrite magnetic rings or beads are specifically designed to suppress high-frequency interference and spike interference on signal lines and power lines, and they also have the ability to absorb electrostatic discharge pulse interference. Whether to use chip magnetic beads or chip inductors mainly depends on the practical application scenarios. Chip inductors are required in resonant circuits. When eliminating unwanted EMI noise, using chip magnetic beads is the best choice.

Application scenarios of chip magnetic beads and chip inductors

Chip inductors: RF and wireless communication, information technology equipment, radar detectors, automotive electronics, cellular phones, pagers, audio equipment, personal digital assistants (PDAs), wireless remote control systems, and low-voltage power supply modules.

Chip magnetic beads: filtering between clock generation circuits, analog circuits, and digital circuits, I/O input/output internal connectors (such as serial ports, parallel ports, keyboards, mice, long-distance telecommunications, local area networks), between RF circuits and easily interfered logic devices, filtering high-frequency conducted interference in power supply circuits, EMI noise suppression in computers, printers, video recorders (VCRS), television systems, and mobile phones.

The unit of magnetic beads is ohms, because the unit of magnetic beads is nominal based on the impedance it produces at a certain frequency, and the unit of impedance is also ohms. The DATASHEET of magnetic beads usually provides characteristic curves of frequency and impedance, with 100MHz as the standard. For example, at a frequency of 100MHz, the impedance of magnetic beads is equivalent to one thousand ohms.

For the frequency band we want to filter, we need to choose magnetic beads with a higher impedance, usually with an impedance of 600 ohms or more  diode