Choke (electronics)

Chokes were frequently used in the design of rectifier power supplies for vacuum tube equipment such as radio receivers or amplifiers.

Radio frequency chokes (RFC) often have iron powder or ferrite cores which increases inductance and overall operation.

[1] They are often wound in complex patterns (basket winding) to reduce self-capacitance and proximity effect losses.

Reducing this noise is frequently done by using a common mode choke - two parallel coil windings on a single core.

Common mode chokes allow differential currents to pass while blocking signals that are affecting both wires.

It achieves this by the placement of windings such that they generate equal but opposite fields that cancel each other out for differential mode signals.

On the other hand, common mode currents see a high impedance path due to the combined inductance of the windings that reinforce each other.

CM chokes are commonly used in industrial, electrical and telecommunications applications to remove or decrease noise and related electromagnetic interference.

To reduce the near magnetic field emission, a twisted winding structure can be applied to the CM choke.

Common-mode choke with two 20 mH windings, rated to handle 2 amperes
An MF or HF radio choke for tenths of an ampere, and a ferrite bead VHF choke for several amperes
A ferrite "bead" choke , consisting of a cylinder of ferrite encircling a computer power cord to block electronic noise
A typical common-mode choke configuration. The common mode currents, i1 and i2, flowing in the same direction through each of the choke windings, creates equal and in-phase magnetic fields which add together. As a result, the choke presents a high impedance to the common mode signal. [ 2 ]