In the product digital circuit EMC design, we often use the magnetic beads, then the principle of magnetic bead filtering and how to use it?
The ferrite material is a magnesium alloy or a ferrous nickel alloy, which has a high magnetic rate, which can be the lowest capacitance of the inductance coil winding in the case of high frequency high resistance. Ferrite materials are usually applied in high frequency, because they primarily inductively inductively, so that the line is small. In high frequency, they mainly reactive characteristic ratio and varies with the frequency. In practical applications, ferrite materials are used as a high frequency attenuator as a radio frequency circuit. In fact, the ferrite is preferably equivalent to resistance and inductance, low frequency lower resistance is shorted, and the inductance impedance in high frequency becomes quite high, so that the current is all by resistance. Ferrite is a consumable device, the high-frequency energy is converted to thermal energy, which is determined by his resistance characteristics.
The ferrite magnetic beads have better high frequency filtering characteristics compared to ordinary inductors. The ferrite exhibits resistance when high frequencies, which is equivalent to a very low quality factor, so that high impedance can be maintained within a relatively wide frequency range, thereby increasing high frequency filtering efficiency.
In the low frequency band, the impedance is composed of inductance, and the low frequency R is small, the magnetic thermal conductivity of the core is high, so that the inductance is large, the electromagnetic interference is reflected, and the magnetic interference is inhibited. The core is small, and the entire device is a low loss, high Q characteristics inductance, which is easy to cause resonance, which may sometimes occur in low frequency sections, sometimes there may be a phenomenon of interference with ferrite magnetic beads.
In the high frequency section, the impedance is composed of the resistance component. As the frequency is increased, the magnetic thermal magnetic permeability is lowered, resulting in the inductance of the inductor, and the sensing component is reduced, but the loss of the core increases, the resistance component increases. The total impedance is increased, and when the high frequency signal is passed through the ferrite, the electromagnetic interference is absorbed and converted into thermal energy.
Ferrite inhibitors are widely used in printed circuit boards, power cords, and data lines. If the ferrite suppression element is added to the power line inlet end of the printed board, high frequency interference can be filtered. Ferrite magnetic rings or magnetic beads are dedicated to inhibiting signal lines, high frequency interference and spike interference on the power line, which also have the ability to absorb electrostatic discharge pulse interference.
Use a slice magnetic bead or a slice inductor is mainly in practical applications. A slice inductor is required in the resonant circuit. When you need to eliminate unwanted EMI noise, use the slice magnetic beads is the best choice. Sipwilled magnetic beads and sliced applications: Slice inductance: RF (RF) and wireless communication, information technology equipment, radar detectors, automotive electronics, cellular phones, pager, audio equipment, PDAS (personal digital assistant), Wireless remote control system and low voltage power supply module, etc. Slice magnetic bead: filter, I / O input / output internal connector (such as serial port, parallel port, keyboard, mouse, long-distance telecommunications, local local area network), radio frequency (RF) circuit Between the logical devices that are susceptible to interference, filtering EMI noise suppression in high frequency conduction interference, computer, printer, video recorder (VCRS), television system, and mobile phones.
The unit of the magnetic bead is ohm because the unit of the magnetic bead is nominally nominally according to the impedance generated in a certain frequency, and the unit of impedance is also ohm. The DataSheet of the magnetic beads generally provides a characteristic graph of frequency and impedance, typically at 100 MHz as a standard, such as the impedance of the magnetic beads in the 100 MHz frequency is equivalent to 1000 ohms. The larger the magnetic bead impedance needs to be selected for the frequency band we have to filter, the better, usually, 600 ohmic impedances.
Also chooses of magnetic beads, it is necessary to pay attention to the flow of the magnetic beads, which generally requires the decline of 80%, and the DC impedance is considered in the power supply circuit.
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