[Switch] How to choose a proper magnetic beads Bead

In the EMC design process of digital circuits, we often use magnetic beads. How can we use magnetic beads?
The ferrite material is an iron-magnesium alloy or iron-nickel alloy, which has a high magnetic conductivity and can be the smallest capacitance generated between the coil winding of an inductor at a high frequency and high impedance. Ferrite Materials are usually used at high frequencies because their main inductance properties make the online loss very small. In high-frequency cases, they primarily exhibit a ratio of the impedance and change with the frequency. In practical application, ferrite material is used as a high-frequency attenuation device for RF circuits. In fact, ferrite is better equivalent to resistance and inductance parallel, low frequency resistance is short-circuited by inductance, high frequency inductance impedance becomes quite high, so that the current is all through the resistance. Ferrite is a device that consumes high-frequency energy and converts it into heat energy. This is determined by its resistance characteristics.
Ferrite Magnetic Beads have better high-frequency filtering characteristics than ordinary inductor. Ferrite presents resistance at high frequencies, which is equivalent to an inductor with low quality factor. Therefore, it can maintain a high impedance within a very wide frequency range to improve the high-frequency filtering efficiency. In the low-frequency section, the impedance is composed of Inductance inductance. Low-Frequency R is very small, and the magnetic permeability of the core is high. Therefore, the inductance is large, and the electromagnetic interference is restrained by reflection; at this time, the loss of the core is small, and the entire device is a low-loss, high Q-characterized inductor, this inductance is easy to cause resonance, so in the low frequency segment, sometimes the interference is enhanced after ferrite beads are used. In the high-frequency band, the impedance is composed of resistance components. As the frequency increases, the magnetic permeability of the core decreases, resulting in reduced inductance and inductance. However, when the loss of the core increases, the resistance component increases, as a result, the total impedance increases. When high-frequency signals pass through ferrite, electromagnetic interference is absorbed and converted into heat energy for dissipation.
Ferrite suppression elements are widely used in printed circuit boards, power cords, and data cables. For example, if a ferrite suppression element is added to the power cord inlet of the printed board, high-frequency interference can be filtered out. Ferrite Magnetic rings or magnetic beads are used to suppress high-frequency interference and Spike interference on signal lines and power cables. They also have the ability to absorb electrostatic discharge pulse interference.
Chip magnetic beads or chip inductor are mainly used in practical applications.
Chip Inductor must be used in the resonant circuit. The use of chip magnetic beads is the best choice to eliminate unwanted EMI noise.
Chip magnetic beads and Chip Inductor applications:
Chip Inductor: RF and wireless communication, information technology equipment, radar detector, automotive electronics, cellular phone, pager, audio equipment, PDAs (Personal Digital Assistant ), wireless Remote Control System and low-voltage power supply module.
Chip magnetic 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 telecommunications, local LAN), RF circuit, and easy-to-work
Among the disturbance logic devices, the Power Supply Circuit filters out high-frequency conduction interference, EMI noise in computer, printer, video recorder (VCRs), TV System and mobile phone.
The unit of the magnetic bead is Ohm, because the Unit of the magnetic bead is nominal Based on the impedance generated at a certain frequency, and the impedance unit is ohm. Datasheet of magnetic beads generally provides characteristic curves of frequency and impedance, which are generally based on 100 MHz. For example, when the frequency is 100 MHz, the impedance of magnetic beads is equivalent to 1000 ohm. For the frequency band that we want to filter, the larger the magnetic beads impedance, the better. Generally, the higher the 600 ohm impedance is selected.
In addition, when selecting the magnetic beads, you need to pay attention to the flow of the magnetic beads. Generally, You need to reduce the amount by 80%. When using the power circuit, you need to consider the impact of the DC impedance on the pressure drop.