PCB circuit design bead selection techniques
Chip beads and chip inductors using reason: the use of chip beads or chip inductors mainly lies in the application. In the resonant circuit requires the use of chip inductors. And when you need to eliminate unwanted EMI noise, the use of chip beads is the best option.
1. Beads in ohms instead of Hunter, it should pay special attention. Because the bead unit is in accordance with its impedance at a frequency generator to the nominal impedance of the unit is ohm. The beads DATASHEET typically provide frequency and impedance characteristic curve, generally 100MHz as standard, such as 1000R 100MHz, meaning that when the magnetic beads 100MHz frequency impedance is equivalent to 600 ohms.
2. Common filter is lossless reactance element constituted, its role in the line is the stop-band frequency signal reflected back to the source, so this type of filter is called reflection filter. When the reflection filter does not match the source impedance, there will be a part of the energy is reflected back to the source, resulting in enhancement of the level of interference. To address this malady can be used in the filter into the online ferrite bead or beads sets, use mayonnaise or ring bead on the high-frequency signal of eddy current losses, the high-frequency component is converted to heat loss. Therefore, magnetic beads and high frequency components actually play absorption, it is sometimes also referred to as absorbent filter.
Different ferrite suppression components have different optimal inhibition frequency range. Typically the higher the permeability, the lower the frequency of inhibition. In addition, the greater the volume of the ferrite, the better the inhibition effect. I love some of the online program, Daniel found: in a certain volume, the long, thin shape than the stubby suppressing effect, the smaller the diameter the better inhibitory effect. But in the case of AC or DC bias current situation, there is also the problem of saturation of ferrite to suppress the larger cross-sectional component, the more difficult and saturated, can withstand greater the drift. When EMI absorption ring / bead differential mode interference suppression, through its current value is proportional to its volume, both disorders causing saturation, reducing the device performance; common mode interference suppression, the power of the two wires (positive and negative) while passing through a magnetic ring, valid signal differential mode
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