An inductor is a passive two-terminal component that stores energy in a magnetic field proportional to the current flowing through it, characterized by its inductance measured in henries (H). It resists changes in current, producing a voltage across its terminals equal to L·(di/dt).
In practice
In embedded power electronics, inductors are a core element of switching regulators (buck, boost, buck-boost). The inductor in a DC-DC converter acts as an energy storage and current-smoothing element: during the switch-on phase it accumulates energy, and during the switch-off phase it releases that energy to the load. Typical values in MCU-power-supply designs range from a few hundred nanohenries to tens of microhenries, with the exact value chosen to set ripple current at the target switching frequency.
Inductors also appear as part of LC filters on ADC supply rails, CAN/Ethernet line filters, and EMI suppression networks. Ferrite beads, which are sometimes used interchangeably with inductors in filtering contexts, are lossy inductors optimized to dissipate high-frequency noise rather than reflect it, and the two should not be blindly substituted for each other.
A frequently overlooked issue in high-speed switching circuits is parasitic inductance in PCB traces, bond wires, and component leads. Even a few nanohenries of stray inductance can cause significant voltage spikes (V = L·di/dt) during fast MOSFET switching transitions. This is covered in depth in the blog post "Turn It On Again: Modeling Power MOSFET Turn-On Dependence on Source Inductance." Gate-drive and power-loop layout must account for these parasitics to avoid ringing, overvoltage stress, and EMI.
Inductors also appear in resonant and oscillator circuits. An LC tank circuit forms the basis of tuned filters and oscillators; the blog post "Metal detection: beat frequency oscillator" demonstrates a practical application where inductance changes caused by a nearby metal object shift the resonant frequency of an LC oscillator, enabling detection. For a broader survey of inductors alongside other passive and active components relevant to embedded work, the blog posts "10 Circuit Components You Should Know" and "Another 10 Circuit Components You Should Know" are useful references.
Frequently asked
How do I choose an inductor value for a buck converter?
The standard formula is L = (Vin - Vout) * Vout / (Vin * f_sw * delta_I_L), where f_sw is the switching frequency and delta_I_L is the desired peak-to-peak ripple current (commonly set to 20-40% of the maximum output current). Higher inductance reduces ripple but increases physical size and can slow transient response. Most DC-DC controller datasheets include a worked example for their recommended operating range.
What is saturation current and why does it matter?
Saturation current is the DC current at which the inductor's inductance drops by a specified amount (commonly 20-30%) because the core material can no longer support additional magnetic flux. If the inductor saturates during normal operation, inductance collapses, ripple current spikes, and the converter may lose regulation or damage the switching
transistor. The inductor's saturation current rating must exceed the peak inductor current, including ripple, under worst-case conditions.
What is DCR and why does it appear in inductor datasheets?
DCR (DC resistance) is the ohmic resistance of the inductor winding wire. It causes I²R power loss and a DC voltage drop proportional to load current. In low-voltage, high-current designs (such as a 1 V / 10 A CPU supply), even 5 mΩ of DCR dissipates 500 mW, so minimizing DCR is important for efficiency. Some synchronous buck controllers use DCR as a lossless current-sensing element by placing a parallel RC network across the inductor.
How does parasitic inductance differ from a discrete inductor?
Any conductor carrying changing current has some inductance. PCB traces, vias, component leads, and bond wires all contribute parasitic inductance, typically in the range of 1-20 nH depending on geometry. Unlike a discrete inductor, this inductance is unintentional and usually unwanted. In fast-switching circuits, stray inductance in the power loop or gate-drive path causes voltage spikes (V = L·di/dt) and ringing, which can exceed device voltage ratings and radiate
EMI.
Can an inductor be used as a sensor?
Yes. Because inductance depends on the permeability and geometry of the surrounding medium, a coil's resonant frequency or impedance shifts when a conductive or ferromagnetic object enters its field. This principle is used in inductive proximity sensors and metal detectors. The blog post 'Metal detection: beat frequency oscillator' walks through a practical implementation where two LC oscillators are compared to detect small inductance shifts caused by nearby metal.
Differentiators vs similar concepts
Inductors are sometimes confused with ferrite beads. Both are inductive components, but a ferrite bead is intentionally lossy: it dissipates high-frequency energy as heat rather than storing and returning it. Ferrite beads are suited for suppressing high-frequency noise on power or signal lines; discrete inductors are suited for energy storage in switching regulators and resonant circuits. Substituting one for the other without checking the impedance-vs-frequency profile and current rating will typically degrade performance. Inductors are also distinct from transformers: a transformer uses two or more coupled windings to transfer energy between circuits with voltage scaling, while a single-winding inductor stores and releases energy within one circuit.
