Inductor

A passive component that stores energy in a magnetic field and resists changes in current.

How it works

An inductor is a passive component that stores electrical energy in a magnetic field when electric current flows through it. Because it takes time for the magnetic field to build and collapse, an inductor inherently opposes any rapid changes in current.

In DC circuits, an inductor initially acts as an open circuit when power is applied, but eventually becomes a near-perfect short circuit once the magnetic field stabilizes. In AC circuits, its resistance to alternating current (called reactance) increases as the frequency of the AC signal increases.

Key Formulas

Induced VoltageV = L × (di/dt)

Voltage equals inductance times the rate of change of current

Common Mistakes

Switching off current to an inductor (like a relay coil) abruptly without a flyback diode. The sudden di/dt causes a massive voltage spike that easily destroys controlling transistors.

Common Variants

10µH RF Choke

A small-value inductor whose high reactance at radio frequencies makes it useful for blocking RF signals from a DC supply line while passing DC freely — a role defined by frequency, not just inductance value.

100mH Audio Inductor

A much larger inductance value than an RF choke, sized to present meaningful impedance already in the audio band — the standard role for the low-pass leg of a passive loudspeaker crossover network.