Inductors

An inductor is a passive electronic component that stores energy in a magnetic field when electric current passes through it. The basic property is inductance, defined as the ratio between the magnetic flux linkage and the current. For a time-varying current, the induced voltage is v = L di/dt, and the energy stored in the magnetic field is E = 1/2 L i^2. In alternating current circuits, the inductor presents an impedance Z = jωL, increasing with frequency and opposing changes in current. In steady direct current, an ideal inductor behaves as a short circuit, though real devices have winding resistance and core losses.

Construction and types: Inductors are formed by winding a conductor, usually copper, around a core. Core materials include air (air-core), ferrite or iron-based materials. Core choice affects inductance, saturation, losses, and size. Common forms include through-hole wire-wound, toroidal, radial or axial lead, and surface-mount devices. Variable inductors use movable cores to adjust inductance.

Applications and related concepts: Inductors are used in filters, tuning circuits, energy storage in switch-mode power supplies, and as chokes to limit current. They also participate in transformers through mutual inductance between windings; in ideal transformers V1/V2 = N1/N2 and I1/I2 = N2/N1. Self-inductance L depends on geometry and material: for a simple solenoid L ≈ μ N^2 A / l, with μ = μ0 μr. Specifications include inductance value, tolerance, DC resistance, saturation current, Q factor, and self-resonant frequency.

Limitations and design considerations: Inductors have parasitic elements such as winding capacitance and core losses that affect high-frequency performance. Saturation occurs when the core cannot support additional magnetic flux, limiting inductance. The self-resonant frequency marks where the inductor ceases to behave as an inductor.