Differences between Chip Inductors and Chip Ferrite Beads

2024-12-29

Inductors are energy storage components, while ferrite beads are energy conversion (consumption) devices. Inductors are commonly used in power filtering circuits, focusing on suppressing conductive interference; ferrite beads are mainly used in signal circuits, primarily for EMI (Electromagnetic Interference) purposes. Ferrite beads are used to absorb high-frequency signals, such as in RF circuits, PLL (Phase-Locked Loop), oscillators, and circuits containing high-frequency memory (DDR, SDRAM, RAMBUS, etc.), which require ferrite beads at the power input. Inductors, as energy storage components, are used in LC oscillation circuits and mid-low frequency filter circuits, with application frequencies rarely exceeding 50 MHz.

Chip Inductor

Inductive components and EMI filter components are widely used in the PCB circuits of electronic devices. These components include chip inductors and chip ferrite beads. This section describes the characteristics of these two types of devices and analyzes their general and specific applications. The benefits of surface mount components are their small package size and ability to meet space requirements. Besides differences in impedance values, current-carrying capacities, and other similar physical characteristics, other performance features of through-hole connectors and surface mount devices are generally the same. When chip inductors are needed, they must achieve two basic functions: circuit resonance and choke reactance. Resonant circuits include resonance generating circuits, oscillation circuits, clock circuits, pulse circuits, waveform generating circuits, etc.

Resonance circuits also include high-Q band-pass filter circuits. For a circuit to resonate, both capacitance and inductance must be present. There is parasitic capacitance at the ends of the inductor, which is caused by the ferrite core acting as a capacitive medium between the two electrodes of the device. In resonant circuits, inductors must have a high Q, narrow inductance deviation, and a stable temperature coefficient to meet the requirements for narrow band, low-frequency temperature drift in resonant circuits. High-Q circuits exhibit sharp resonance peaks. A narrow inductance bias ensures that the deviation of the resonant frequency is minimized. A stable temperature coefficient ensures that the resonant frequency has stable temperature variation characteristics. The differences between standard radial lead inductors, axial lead inductors, and chip inductors are purely in packaging. The inductor structure includes a coil wound on dielectric materials (usually aluminum oxide ceramic materials) or a hollow coil wound on ferromagnetic materials.

In power applications, when used as a choke, the main parameters of inductors are DC resistance (DCR), rated current, and low Q. When used as filters, wide bandwidth characteristics are desired; thus, high-Q characteristics are not required. Low DCR ensures minimal voltage drop, and DCR is defined as the direct current resistance of the component without AC signal.

Chip Ferrite Bead

The main function of chip ferrite beads is to eliminate RF noise present in transmission line structures (PCB circuits). RF energy is the AC sine wave component superimposed on the DC transmission level, where the DC component is the useful signal, while the RF energy is unwanted electromagnetic interference that travels and radiates along the line (EMI). To eliminate this unwanted signal energy, chip ferrite beads act as high-frequency resistors (attenuators) that allow DC signals to pass through while filtering out AC signals. Usually, high-frequency signals are above 30 MHz; however, low-frequency signals can also be affected by chip ferrite beads.

Chip ferrite beads are made from soft magnetic ferrite materials, creating a monolithic structure with high volumetric resistivity. The eddy current loss is inversely proportional to the resistivity of the ferrite material, and eddy current losses vary proportionally with the square of the signal frequency.

Benefits of Using Chip Ferrite Beads

Miniaturization and lightweight design. High impedance in the RF noise frequency range to eliminate electromagnetic interference in transmission lines. Closed magnetic circuit structure to better eliminate signal coupling. Excellent magnetic shielding structure. Reduced DC resistance to avoid excessive attenuation of useful signals.

Significant high-frequency characteristics and impedance characteristics (better RF energy elimination). Elimination of parasitic oscillation in high-frequency amplification circuits. Effective operation in frequency ranges from several MHz to hundreds of MHz. To choose the right ferrite bead, the following points must be considered: what is the frequency range of the unwanted signals? Who is the noise source? What level of noise attenuation is needed? What are the environmental conditions (temperature, DC voltage, structural strength)? What are the circuit and load impedances? Is there space on the PCB to place the ferrite bead? The first three can be assessed by observing impedance frequency curves provided by manufacturers. In the impedance curves, three lines are essential: resistance, reactance, and total impedance. The total impedance is described by Z = √[R² + (2πfL)²]. Typical impedance curves can be referenced in the ferrite bead's datasheet.

Through this curve, select a ferrite bead model that exhibits maximum impedance within the frequency range where noise needs to be attenuated while minimizing signal attenuation at low frequencies and DC. Chip ferrite beads can have their impedance characteristics impacted under excessive DC voltage, as well as by high ambient temperature increases or excessive external magnetic fields.

Reasons for Using Chip Ferrite Beads and Chip Inductors

Whether to use a chip ferrite bead or a chip inductor mainly depends on the application. Chip inductors are needed in resonant circuits, while chip ferrite beads are the best choice for eliminating unwanted EMI noise.

Applications of Chip Ferrite Beads and Chip Inductors:

Chip Inductor: RF (Radio Frequency) and wireless communications, IT equipment, radar detectors, automotive electronics, cellular phones, pagers, audio devices, PDAs (Personal Digital Assistants), wireless remote control systems, and low-voltage power supply modules, etc.

Chip Ferrite Bead: Clock generation circuits, filtering between analog and digital circuits, I/O internal connection (such as serial ports, parallel ports, keyboards, mice, long-distance telecommunications, local area networks), filtering high-frequency conductive interference in power circuits, EMI noise suppression in computers, printers, VCRs (Video Cassette Recorders), TV systems, and mobile phones.

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