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What is Choke Coil?

10/31/2013 4:10:24 PM | by Anonymous

Choke Coils

Choke coil is a part used in the electrical circuits to allow DC current to flow through while blocking AC current from passing. These choke coils are used in a number of electrical devices and when used as part of a radio’s circuitry, it will fall into one of two frequency classes such as radio or audio. These are usually used in circuits with higher frequencies use with different core materials than those used in lower frequency circuits.


In electronics, a choke is a version of a passive two terminal electronic component that called an inductor which is designed specifically for blocking higher frequency alternating current (AC) in an electrical circuit while allowing the lower frequency or DC current to pass.


A choke usually consists of a coil of insulated wire that is often wound on a magnetic core although some consist of a donut shaped “bead” of ferrite material strung on wire. The low electrical resistance allows DC and AC to pass with little power loss but it can limit the amount of AC passing through it due to its reactance. The name comes from blocking – “choking” – high frequencies while passing low frequencies. It is a functional name and is the same inductor that is often called a choke.


During the process of sending a signal through the circuit, the idea is to let the desired signal go through while filtering out the other unwanted signals. There is one type of unwanted signal which is the common mode noise that filters out by a common mode choke coil. Power lines are example of a source of common mode noise and without a choke coil, the power line would create a lot of electrical noise as it traveled to its destination. This would be received on the other end and possibly case interference with the signal.


The choke coil works because it can act as an inductor. When the current pass through will change as AC currents creates a magnetic field in the coil that works against that current. This is known as inductance and blocks most of the AC current from passing through. This result to the currents that do not change such as DC currents can continue passing through while those currents that are blocked by the magnetic field.


Choke coils are used to filter higher frequencies that may use a ferrite core or an air-core while lower frequency coils may use an iron core. This material in the core determines the strength of the magnetic field and the inductance rate of the coil. Inductors are similar to capacitors with only one key difference in how they work. A choke coil stores the electric charge in the magnetic field created around it instead of on any specific part of the coil. Both parts are used in the electronic circuitry but capacitors are typically store electric charges while these coils filter them.


When choosing the best type to use in a circuit, the engineer will look at the voltage and the DC resistance of the coil as well as the level of inductance. These factors will determine which choke coil will most efficiently pass through the correct currents while blocking the unwanted ones.

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