Ferrite beads have better high frequency filtering characteristics than ordinary inductors. Ferrite exhibits electrical resistance at high frequencies, which is equivalent to an inductor with a low quality factor, so it can maintain a high impedance over a relatively wide frequency range, thereby improving high-frequency filtering performance.
In the low frequency band, the impedance is composed of the inductive reactance of the inductor. R is small at low frequencies, and the magnetic permeability of the magnetic core is high. Therefore, the inductance is large, L plays a major role, and electromagnetic interference is reflected and suppressed; and magnetic The loss of the core is small, and the whole device is a low-loss, high-Q inductor. This kind of inductance is easy to cause resonance. Therefore, in the low frequency range, the interference enhancement after the use of the ferrite bead may sometimes occur.
In the high frequency band, the impedance is composed of a resistance component. 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 inductive component. However, the loss of the core increases and the resistance component increases. This causes the total impedance to increase, and when the high frequency signal passes through the ferrite, the electromagnetic interference is absorbed and converted into heat energy to dissipate.
Ferrite suppression components are widely used in printed circuit boards, power lines, and data lines. High frequency interference can be filtered out by adding a ferrite suppression component to the input end of the power strip of the printed board. Ferrite magnetic rings or magnetic beads are designed to suppress high-frequency interference and spike interference on signal lines and power lines. They also have the ability to absorb electrostatic discharge pulse interference.
The use of chip beads or chip inductors is mainly in practical applications. A chip inductor is required in the resonant circuit. The use of chip beads is the best choice when eliminating unwanted EMI noise. Application of Chip Beads and Chip Inductors: Chip Inductors: Radio Frequency (RF) and Wireless Communications, Information Technology Equipment, Radar Detectors, Automotive Electronics, Cellular Phones, Pagers, Audio Equipment, PDAs (Personal Digital Assistants), Wireless remote control system and low voltage power supply module. Chip Beads: Clock generation circuit, filtering between analog circuit and digital circuit, I/O input/output internal connector (such as serial port, parallel port, keyboard, mouse, long distance telecommunication, local area network), radio frequency (RF) circuit Between high-frequency conducted interference in the power supply circuit and EMI noise suppression in computers, printers, video recorders (VCRS), television systems, and mobile phones, and interference-prone logic devices.
The unit of the magnetic bead is ohm, because the unit of the magnetic bead is nominal according to the impedance it produces at a certain frequency, and the unit of impedance is also ohm. The magnetic field DATASHEET generally provides a characteristic curve of frequency and impedance, generally based on 100MHz. For example, the impedance of the magnetic bead is equivalent to 1000 ohms at a frequency of 100MHz. For the frequency band we want to filter, the larger the impedance of the bead is, the better. Generally, the impedance above 600 ohms is selected.
In addition, when selecting the magnetic beads, it is necessary to pay attention to the flux flow of the magnetic beads. Generally, 80% of the derating is required. When using the power supply circuit, the influence of the DC impedance on the voltage drop should be considered.
