Selection of chip beads and chip inductors
The function of chip beads is mainly to eliminate the RF noise present in the transmission line.
The chip magnetic beads are composed of soft ferrite materials and form a monolithic structure with high volume resistivity. Eddy current loss is inversely proportional to the resistivity of ferrite materials. Eddy current loss is proportional to the square of the signal frequency.
The advantages of using chip magnetic beads:
Small and light. It has high impedance in the frequency range of radio frequency noise and eliminates electromagnetic interference in the transmission line. Closed magnetic circuit structure can better eliminate signal crosstalk. Excellent magnetic shielding structure. Reduce the DC resistance to avoid excessive attenuation of useful signals.
High frequency characteristics and impedance characteristics. Eliminate parasitic oscillations in high-frequency amplifier circuits. Effectively work in the frequency range of several MHz to several hundred MHz. To select the magnetic beads correctly, you must pay attention to the following points: What is the frequency range of the unwanted signal? Who is the source of noise? How much noise attenuation is needed. What are the environmental conditions. What is the circuit and load impedance. Is there space to place the magnetic beads on the PCB board? The total impedance is described by ZR22πfL()2+:=fL. The typical impedance curve can be found in the DATASHEET of the magnetic beads.
Through this curve, choose the magnetic bead model that has the largest impedance in the frequency range where the noise is to be attenuated and the signal attenuation is as small as possible under low frequency and DC. Chip magnetic beads will affect the impedance characteristics under excessive DC voltage. In addition, if the operating temperature rises too high or the external magnetic field is too large, the impedance of the magnetic beads will be adversely affected.
The reason for using chip magnetic beads or chip inductors: whether to use chip magnetic beads or chip inductors mainly depends on the application. Chip inductors are required in the resonant circuit. When it is necessary to eliminate unnecessary EMI noise, using chip magnetic beads is the best choice. Application of chip beads and chip inductors: Chip inductors: RF and wireless communications, information technology equipment, radar detectors, automotive electronics, cellular phones, pagers, audio equipment, PDAs, wireless remote control systems, and low-voltage power supply modules, etc. . Chip beads: clock generation circuit, filtering between analog circuits and digital circuits, I/O input/output internal connectors, between radio frequency circuits and logic devices that are susceptible to interference, and filter high-frequency conduction interference in the power supply circuit EMI noise suppression in computers, printers, video recorders, TV systems and mobile phones.