Choke (electronics)

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A choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. They are inductances that isolate AC frequency currents from certain areas of a radio circuit. Chokes depend upon the property of self-inductance for their operation. They are used to block alternating current while passing direct current. Common-mode choke coils are useful in a wide range of prevention of electromagnetic interference (EMI) and radio frequency interference (RFI) from power supply lines and for prevention of malfunctioning of electronic equipment.

A choke on a USB cable

[edit] Types and construction

Chokes used in radio circuits are divided into two classes-those designed to be used with audio frequencies, and the others to be used with radio frequencies

Audio frequency coils, usually called A.F. chokes, have ferromagnetic iron cores to increase their inductance.

Chokes for higher frequencies (ferrite chokes or choke baluns) have ferrite cores. Chokes for even higher frequencies have air cores.

Radio frequency coils, (R.F. chokes), usually don't have iron cores. In high power service so much heat would be produced in making and destroying the field in the core that the coil would burn up.