As passive components depending on the property of self-inductance, choke coils operate based on the generation of an electromotive force (EMF) in a circuit that results from the changing of the current in that circuit.
Choke coils are electrical coils that work to block common-mode currents while passing differential, or equal but opposite, currents. Although they provide a very specific function, choke coils can be utilized in a broad range of applications including: power generation, in order to protect power lines from electromagnetic interference (EMI) or radio frequency interference (RFI); automotive, for use in engine applications; electronics, to protect electrical devices from EMI and RFI that could cause them to malfunction; and HVAC, for use in equipment such as furnaces, air conditioners and blowers.
There are several different types of choke coils and one of the main differences in construction between the types is the core material, which can include iron powder, ferromagnetic, non-magnetic and ferrite. What metal is chosen depends on the conductivity level desired.
Often used in EMI and RFI interference protection applications, there are two main categories of choke coils utilized in radio circuits: audio frequency coils (A.F. chokes) and solid-state chokes (SSC), which are also known as electronic ballast or electronic chokes. A.F. chokes are, as the name suggests, designed to be used with audio frequency applications, and as a result have a core constructed from ferromagnetic iron that allows for increased induction capabilities, much like the induction coil.
Within A.F. chokes, there can be other categorizations based on how high of a frequency the choke coil is able to function with. For moderately high frequencies, A.F. chokes typically have a core constructed from iron powder or ferrite, while for very high frequencies A.F. chokes most often have a core constructed from non-magnetic cores. The non-magnetic cores could be so simple as to only require air surrounding the coil. When it comes to SSC, they are capable of operating with even higher frequencies than A.F. chokes.
In addition, SSC are capable of reducing the high noise levels typically associated with higher frequencies. Additional types of choke coils include medium frequency (MF) radio chokes, high frequency (HF) radio chokes and very high frequency (VHF) chokes.