Inductors are metal coils used in circuits. They are able to generate magnetic fields when they carry current. They are also able to induce magnetic fields in wires that are near them. Inductors that are used to help filter signals are called chokes.

Both small and large inductors are used as chokes. Their ratings include their value, the maximum current they can handle and their maximum resistance to current flow. Some chokes have iron cores inside of them.

Choke filters help reduce AC voltages to very small values, so that a load component such as a resistor will basically receive DC voltages. These unwanted AC signal fluctuations are called ripples. Chokes are very often used to filter out radio frequencies.

The size of the choke determines the cutoff frequency or boundary. A large choke means a lower cutoff frequency, and a small choke means a higher cutoff frequency. Large ones are better for more precise filtering of unwanted 120 hertz signals and higher from wall outlets, for example.

Choke circuits are formed from a single inductor or a combination of an inductor and one or more capacitors. Choke circuits are low-pass filters since they weed out high frequencies and pass lower ones through.

Chokes filter out the AC ripples in power supplies to help ensure a steady DC output. Chokes are also found in circuits such as Colpitts, Hartley, and Clapp oscillators.