The following items should be noted when selecting power inductors at the design stage.

1. First, consider the application field. Power inductors are widely used in DC-DC conversion circuits, power supply circuits, audio filter circuits, etc.

2. For DC-DC conversion circuits, the selection of power inductors should be determined according to the frequency of the external signal, and its self-resonant frequency should be greater than the frequency of the signal.

3. The selection of inductors should be consistent with the design of the circuit. For example, in DC-DC conversion circuits, power inductors are used for energy storage and oscillation suppression. Generally, the larger the inductance value, the stronger the energy storage and filtering effect. However, at the same time, the larger the inductance value, the larger the RDC of the inductor, which reduces energy efficiency and cannot be used for high current applications.

4. The power inductor should be selected according to the size of the loop current. Both currents should be considered at the same time. When selecting a power inductor, the smaller one should be used as the rated current.

5. The size of the power inductor should be selected according to the pad layout and space of the application.

The main electrical parameters of power inductors include L, DCR, saturation current (Isat), thermal rated current (Irms), and SRF.

L: L is the nominal inductance of the inductor. Due to the existence of distributed capacitance, the L value is frequency-dependent. The tolerance of the inductor is generally divided into two levels: M (±20%) and N (±30%).

DCR: DC resistance, that is, the DC resistance of the wire between the two poles.

Saturation Current (Isat): Under continuous current, the inductance will decrease. Saturation current (Isat), also known as the DC superposition current, is defined as the current when the inductance decreases by 30%.

Heating Rating Current (Irms): Under continuous current, the component body temperature will rise. Thermal rated current is defined as the current that causes the component body temperature to rise by 40℃ from the ambient temperature of 20℃.

SRF (Self-Resonant Frequency): SRF is defined as the frequency at which an inductor reaches resonance due to the interaction of inductance and stray capacitance.

Sparameters are also called the scattering parameters, which are used for evaluating the performance of DUT reflecting and transmitting signals. The S parameters which contain the amplitude and phase information of the signals are defined as the ratio of two plural.

Sparameters are usually expressed as: S (output, input)
Output: output port number of DUT
Input: input port number of DUT
For example, S21 means the ratio of the DUT’s output signal in port 2 and the input signal in port 1, and the output signal and input signal are plurals.
First of all, at the high frequency range, S parameters can be easily and S parameters can correlate with many other familiar parameters such as gain, loss, and reflection coefficient and so on;
Second, the H, Y, or Z parameters can be calculated using the S parameters;
Finally, the S parameters are suitable for all kinds of simulation software.

The symbols for chip beads and inductors in a circuit are the same, but they are different devices. The magnetic beads are in ohms (Ω) and the inductors are in Hines (H).
Chip beads are made of oxygen magnets, inductors are made of cores and coils, chip beads convert AC signals into heat energy, inductors store AC and slowly release it, so inductors store energy, magnetic beads are energy conversion devices.
Chip beads mainly solve the problem of radiation interference. signal line multi-use magnetic beads, some high-frequency circuits such as RF, oscillating circuit, DDR SDRAM and so on need to add chip beads in the power supply input part.
Inductors mainly solve the problem of conduction interference, high-frequency inductors are mainly used in low-and medium-frequency filter circuits, RF matching, etc.

We usually define the tolerance with specific letters in inductor naming .such as the following tolerances of power inductors, J: 5% ; K: 10% ; M: 20% ; N: 30%.