What are Chokes and Their Use in Electrical Applications?
In the realm of electronics, a choke is a type of inductor that may be implemented for the means of managing the flow of current. Generally, such devices are capable of blocking high-frequency alternating currents while permitting the flow of both direct current and lower-frequency alternating current. In this blog, we will discuss the construction and functionality of chokes, allowing you to better understand their uses and functionalities. In general, a choke consists of an insulated wire coil that is wound around a magnetic core, though other types may take advantage of a ferrite material that is strung on a wire. As frequency increases, so too does the impedance of the device. Despite featuring low power loss in regard to passing AC and DC, the reactance of chokes limit the amount of AC that they may transmit.
The naming of such devices comes from how they function, blocking or choking the transmission of high frequencies while enabling the flow of low frequencies. When used in electronic filters or tuned circuits, however, a choke device is known as an inductor. Inductors may be designed to be used as chokes, typically featuring the lack of low-loss construction that is generally required of inductors when in tuned circuits and filters.
When deciding between chokes for a particular application, such components may either come in the form of audio or radio frequency chokes. Audio frequency chokes (AFC) are those constructed from ferromagnetic cores, ensuring that their inductance remains steady. Similar to transformers, audio frequency chokes take advantage of an iron core which increases inductance for a given volume of the core. With their design, audio frequency chokes commonly find use in vacuum tube equipment where they assist in the operations of radio receivers or amplifiers. When implemented in direct-current motor controls, an audio frequency choke will produce direct current while assisting electrolytic capacitors to remove AC voltage ripple. Smaller chokes, meanwhile, are commonly found in switching power supplies where they may remove higher-frequency switching transients from an output. In order to achieve this, such chokes utilize toroidal ferrite cores.
Radio frequency chokes (RFC), meanwhile, feature either iron powder or ferrite cores which bolster inductance and overall operation. To minimize self-capacitance and proximity effect losses, radio frequency chokes are typically wound in complex patterns such as basket winding patterns. For higher frequencies, non-magnetic cores may be used for low inductance operations. The ferrite bead is a more modernized type, capable of eliminating digital RF noise from lines. Generally, ferrite beads are commonly found in computer cables.
Common-mode chokes are another type, featuring two coils that are wound around a single core. Such assemblies are quite useful for the suppression of electromagnetic interference (EMI) and radio frequency interference (RFI) that source from power supply lines. Blocking common-mode currents, the CM choke is specifically designed for passing differential currents. CM Chokes are often found in industrial, electrical, and telecommunication systems where they mitigate noise and electromagnetic interference.
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