Choke (electronics)

In electronics, a choke is an inductor used to block higher-frequency alternating currents (AC) while passing direct current (DC) and lower-frequency ACs in a circuit. A choke usually consists of a coil of insulated wire often wound on a magnetic core, although some consist of a doughnut-shaped ferrite bead strung on a wire. The choke's impedance increases with frequency. Its low electrical resistance passes both AC and DC with little power loss, but its reactance limits the amount of AC passed. The name comes from blocking—"choking"—high frequencies while passing low frequencies. It is a functional name; the name "choke" is used if an inductor is used for blocking or decoupling higher frequencies, but the component is simply called an "inductor" if used in electronic filters or tuned circuits. Inductors designed for use as chokes are usually distinguished by not having low-loss construction (high Q factor) required in inductors used in tuned circuits and filtering applications. Chokes are divided into two broad classes: Audio frequency chokes—designed to block audio and power line frequencies while allowing DC to pass Radio frequency chokes—designed to block radio frequencies while allowing audio and DC to pass. Audio frequency chokes usually have ferromagnetic cores to increase their inductance. They are often constructed similarly to transformers, with laminated iron cores and an air gap. The iron core increases the inductance for a given volume of the core. Chokes were frequently used in the design of rectifier power supplies for vacuum tube equipment such as radio receivers or amplifiers. They are commonly found in direct-current motor controllers to produce direct current (DC), where they were used in conjunction with large electrolytic capacitors to remove the voltage ripple (AC) at the output DC. A rectifier circuit designed for a choke-output filter may produce too much DC output voltage and subject the rectifier and filter capacitors to excessive in-rush and ripple currents if the inductor is removed.