Inductor

An inductor is a coil of wire. When current flows through it, it builds up a magnetic field, storing energy. When the current tries to change, the field pushes back, resisting the change. That makes inductors good at smoothing current, storing energy for brief moments, and blocking high-frequency noise while letting steady current pass. Their size is measured in henries.

To make one, copper wire, coated with a thin layer of enamel so the turns don't short together, is wound around a core of ferrite. A common shape is a drum: a small ferrite spool, with the wire wound around its waist and the ends attached to metal terminals. The ferrite concentrates the magnetic field, so the coil stores far more energy than it would in air, letting the part stay small. Many inductors also have a ferrite sleeve or a molded magnetic powder around them to keep the field from leaking out. More turns, or a better core, means more inductance.

On the power supply board, inductors filter noise from the mains and store and release energy in the converters. On the main board, they work with switching regulators to turn one voltage into the steady lower voltages the chips need.