The difference of SMD chip inductor and SMD chip bead inductor

The difference of SMD chip inductor and SMD chip bead inductor

Inductance is an energy storage element, and magnetic beads are energy conversion (consumption) devices. Inductors are mostly used in power filter circuits, focusing on suppressing conductive interference; magnetic beads are mostly used in signal circuits, mainly for EMI. Magnetic beads are used to absorb ultra-high frequency signals, such as some RF circuits, PLL, oscillation circuits, including ultra-high frequency memory circuits (DDR, SDRAM, RAMBUS, etc.) all need to add magnetic beads in the input part of the power supply, while inductance is an energy storage element, which is used in LC oscillation circuits, low and medium frequency filter circuits, and its application frequency range is seldom more than 50 MHz.

1. Chip inductors:

Inductive components and EMI filter elements will be widely used in PCB circuit of electronic equipment. These components include chip inductors and magnetic beads. The characteristics of these two devices are described below and their general and special applications are analyzed. The advantages of surface mounted components lie in the small package size and the ability to meet the actual space requirements. In addition to the differences in impedance, current carrying capacity and other similar physical characteristics, the other performance characteristics of through-hole connectors and surface mounted devices are basically the same. When chip inductors are needed, inductors are required to achieve the following two basic functions: circuit resonance and choke reactance. Resonance circuit includes resonance generation circuit, oscillation circuit, clock circuit, pulse circuit, waveform generation circuit and so on. The resonant circuit also includes a high Q bandpass filter circuit. In order to make the circuit resonant, capacitance and inductance must exist in the circuit at the same time. Parasitic capacitance exists at both ends of the inductor, which is due to the fact that the ferrite body between the two electrodes of the device is equivalent to the capacitive medium. In resonant circuit, inductance must have high Q, narrow inductance deviation and stable temperature coefficient to meet the requirements of narrow band and low frequency temperature drift of resonant circuit. High Q circuit has sharp resonance peak. Narrow inductance bias ensures that the resonance frequency deviation is as small as possible. The stable temperature coefficient ensures that the resonant frequency has a stable temperature change characteristic. The difference between standard radial inductance and axial inductance and chip inductance is only due to the different packaging. Inductance structures include winding coils on dielectric materials (usually alumina ceramics), or hollow coils and winding coils on ferromagnetic materials. In power applications, when used as choke coil, the main parameters of inductance are DC resistance (DCR), rated current and low Q value. When used as a filter, the wide bandwidth characteristic is desired, so the high Q characteristic of inductor is not needed. Low DCR guarantees minimum voltage drop. DCR is defined as DC resistance of components without AC signal.

2. Sheet beads:

The function of sheet beads is mainly to eliminate RF noise existing in transmission line structure (PCB circuit). RF energy is the AC sine wave component superimposed on the DC transmission level. DC component is the useful signal needed, while RF energy is the useless electromagnetic interference transmission and radiation along the line (EMI). To eliminate these unwanted signal energies, a chip magnetic bead is used to act as a high-frequency resistor (attenuator), which allows DC signals to pass through and filter out AC signals. Usually the high frequency signal is above 30MHz, but the low frequency signal is also affected by the chip magnetic beads.

The sheet magnetic beads consist of soft magnetic ferrite materials and form a unique structure with high volume resistivity. The eddy current loss is inversely proportional to the resistivity of ferrite materials. The eddy current loss is proportional to the square of the signal frequency.

3. Benefits of using sheet magnetic beads:

miniaturization and lightweight. It has high impedance in the frequency range of radio frequency noise and eliminates electromagnetic interference in transmission lines. Closed magnetic circuit structure, better eliminate the signal series winding. Excellent magnetic shielding structure. Reduce DC resistance to avoid excessive attenuation of useful signals.

Significant high frequency characteristics and impedance characteristics (better elimination of RF energy). Eliminate parasitic oscillation in high frequency amplifier circuit. Effective operation in several MHz to several hundred MHz frequency range. In order to select the magnetic beads correctly, we must pay attention to the following points: the frequency range of unnecessary signals. Who is the noise source? How much noise attenuation is needed. What are the environmental conditions (temperature, DC voltage, structural strength). What is the impedance of the circuit and load? Is there room for magnetic beads to be placed on the PCB board? The first three can be judged by observing the impedance frequency curve provided by the manufacturer. In the impedance curve, three curves are very important, namely resistance, inductance and total impedance. The total impedance is described by Z=[R2+(2pi fL)2]1/2. Typical impedance curves can be found in the DTASHEET of magnetic beads.

Through this curve, the magnetic beads with maximum impedance in the frequency range of desired noise attenuation and minimum signal attenuation at low frequency and DC are selected. In addition, if the working 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 and chip inductors is that the use of chip magnetic beads or chip inductors mainly depends on the application. Chip inductors are needed in resonant circuits. When the unnecessary EMI noise needs to be eliminated, the use of sheet magnetic beads is the best choice.

Application occasions of chip magnetic beads and chip inductors: chip inductors: radio frequency (RF) and wireless communication, information technology equipment, radar detector, automotive electronics, cellular telephone, pager, audio equipment, PDAs (personal digital assistant), wireless remote control system and low voltage power supply module, etc. Chip magnetic beads: filter between clock generating circuit, 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 and logic equipment which are vulnerable to interference, filter high frequency conduction interference in power supply circuit, computer, printer, video recorder (VCRS), Television Department EMI Noise Suppression in Tonghe Mobile Phone.

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