What are the differences between inductors and beads?

These two components, inductors and beads, have similar shapes and sometimes similar functions, and many people refer to both of them as " Isolating DC signals and transmitting AC signals. ", confusing them. In fact, in terms of principle and application, there are significant differences between inductors and beads.

The magnetic material of inductors is open, and part of the magnetic lines (magnetic lines) pass through the core and part through the air, which will cause magnetic field interference to the surrounding space (some inductors also have shielding functions). The magnetic material of the beads is closed, and almost all the magnetic lines are enclosed in the magnetic ring, and the beads are "cleaner", as shown in Figure 1-18, with the main differences as follows.

Figure 1-18 Inductor and Bead

1. The unit of inductor is Henry (H), and the unit of bead is impedance (Ω). What is usually marked in the bead manual is the impedance value at 100MHz. Note that an important thing is that even if the parameters of the beads are the same, their filtering performance may be greatly different. This is because the parameters of the beads are marked with the impedance of a specific frequency point (120/100MHz), and even if the impedance of this frequency point is the same, the impedance at other frequency points will be varied, such as the two different beads in Figure 1-19, both of which have a parameter of 120Ω@100MHz, but obviously the blue bead has a higher impedance at high frequencies.

 

Figure 1-19 Different Beads Impedance Frequency Curve

2. The impedance of the beads is the result of the combined effect of reactance X (inductive reactance) and resistance R. At low frequency, reactance X dominates, and at high frequency, resistance R dominates. Inductors are mostly used in low frequency bands (50 MHz), while beads are mostly used in high frequency filtering scenarios. The resistance R of the beads absorbs noise and converts it into heat, so the unit of the beads is ohm.

3. The filtering principle of inductor is to convert electrical energy into magnetic energy, and then convert the magnetic energy back into electrical energy (noise) or radiation (Electromagnetic Interference, EMI). Beads convert electrical energy into heat energy, and beads are more "clean" filtering components.

4. Inductors are energy storage components, which may form a second-order oscillation circuit with capacitor when filtering, which may lead to system instability; while beads are energy consumption components (R), and basically do not self-excite oscillation when working with capacitors.

 

In short, inductors work in the frequency band where impedance is far greater than resistance, at which impedance is mainly reactance, and its unit is inductive quantity H, and impedance is the main component, and resistance component is very small. Beads mainly work in the frequency band where resistance is greater than impedance, and resistance is the main component, so the unit of beads is ohm. At the same time, due to the small amount of impedance and energy storage, we say that beads mainly consume energy through resistance. When choosing beads, we should focus on the high frequency band, and carefully select beads according to the impedance frequency curve of beads and the target noise.