Trystan Casey
In electronics, a choke is a type of inductor used to block higher-frequency alternating currents (AC) while allowing direct currents (DC) and lower-frequency ACs to pass through a circuit. Chokes are used in audio circuits and power supplies to reduce noise and improve signal quality. They are also used to suppress unwanted RFI (radio frequency interference) that could affect the performance of electronic devices. Chokes are commonly used in industrial, electrical, and telecommunications applications to remove or decrease noise and electromagnetic interference. They are often used in conjunction with large electrolytic capacitors to remove voltage ripple (AC) at the output DC.
| Characteristics | Values |
|---|---|
| Definition | A choke is a type of inductor that blocks higher-frequency alternating currents (AC) while passing direct currents (DC) and lower-frequency ACs. |
| Function | Chokes provide high inductance paths in circuits, limiting the quantity of current flowing through the circuit. |
| Construction | Chokes are typically constructed with a coil of insulated wire wound around a magnetic core. |
| Applications | Chokes are used in audio circuits, power supplies, and high-frequency circuits to reduce noise and improve signal quality. They are also used to suppress RFI and EMI interference. |
| Types | Common types of chokes include common-mode (CM) chokes and radiofrequency (RF) chokes. |
| Performance | Chokes can provide attenuation, signal integrity, and noise reduction over a wide range of currents and frequencies. |
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What You'll Learn
Choke construction and design
Typically, a choke is constructed with a coil of insulated wire wound around a magnetic core. This core is often made of iron or ferrite and is shaped like a doughnut or toroid. The number of turns of the insulated wire, usually copper, around the core is an important aspect of choke design. Chokes with a large number of turns have increased inductance, which is essential for their functionality.
The construction of the core is also a key consideration in choke design. Laminated iron cores are commonly used to minimise eddy current losses. These cores are constructed with thin layers of iron laminated together, reducing the continuous paths for eddy currents and thus decreasing power loss. Additionally, the core may have an air gap to further enhance inductance for a given volume.
Radio frequency chokes (RFC) often have iron powder or ferrite cores, which increase inductance and overall performance. For very high frequencies, non-magnetic cores are used, and the choke construction prioritises low inductance. RFCs may be wound in complex patterns, such as basket winding, to reduce self-capacitance and proximity effect losses.
Common-mode (CM) chokes are another important type of choke used to suppress electromagnetic interference (EMI) and radio frequency interference (RFI). They consist of two parallel coil windings on a single core. The placement of the windings ensures that the magnetic flux generated by differential-mode currents cancels out, resulting in low impedance for these currents. In contrast, common-mode currents encounter high impedance due to the combined inductance of the windings.
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How chokes function
Chokes are a type of inductor with a specific function and design. They are used to block higher-frequency alternating currents (AC) while allowing direct currents (DC) and lower-frequency ACs to pass through. They get their name from this function, as they “choke” or block high frequencies while passing low frequencies.
Chokes usually consist of a coil of insulated wire wound around a magnetic, doughnut-shaped core. The choke's impedance increases with frequency. Its low electrical resistance allows both AC and DC to pass with minimal power loss, but its reactance limits the amount of AC that can pass through.
Chokes are commonly used in industrial, electrical, and telecommunications applications to reduce noise and electromagnetic interference (EMI) on power supply lines. They are also used in direct-current motor controllers to produce DC and remove voltage ripple (AC) at the output.
A common-mode (CM) choke is a specific type of choke that acts on common-mode signals. It is designed to suppress EMI and radio frequency interference (RFI) on high-current wires, such as power supply lines, to prevent unwanted operation. CM chokes achieve this by using two parallel coil windings on a single core, which generate equal but opposite fields that cancel each other out for differential mode signals.
Chokes also have applications in waveguides, where they are used to enhance or inhibit the propagation of specific modes.
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Applications of chokes
Chokes have various applications in electrical circuits. They are used to block higher-frequency alternating currents (AC) while allowing direct currents (DC) and lower-frequency ACs to pass through. This is achieved through the choke's low electrical resistance, which allows both AC and DC to pass with minimal power loss, while its reactance limits the amount of AC that can pass through.
Chokes are commonly used in industrial, electrical, and telecommunications applications to remove or decrease noise and electromagnetic interference. They are also used to suppress radio frequency interference (RFI) and electromagnetic interference (EMI) on power supply lines, which can cause unwanted operations. This is achieved through the use of common-mode (CM) chokes, which allow differential currents to pass while blocking signals that affect both wires.
Chokes are also used in the design of rectifier power supplies for vacuum tube equipment, such as radio receivers or amplifiers. They are found in direct-current motor controllers to produce DC and remove voltage ripple (AC) at the output DC. Additionally, chokes are used in switching power supplies to remove higher-frequency switching transients from the output.
Waveguide chokes are another type of choke with a specific application. They are designed to enhance or inhibit the propagation of specific modes in waveguides.
Furthermore, chokes are used in computers to keep circuits energised and in switching power supplies. Radiofrequency (RF) chokes rely on larger inductor sizes to block low-frequency signals effectively.
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Choke circuit diagrams
Chokes typically consist of a coil of insulated wire wound around a magnetic core, resembling a doughnut or toroid shape. This construction is designed to impede high-frequency AC while permitting the passage of DC and lower-frequency AC with minimal power loss. Chokes are commonly employed in electrical circuits to manage and stabilise current and voltage.
One important application of choke circuit diagrams is in the design of rectifier power supplies for vacuum tube equipment, such as radio receivers and amplifiers. Chokes are used in conjunction with capacitors to eliminate voltage ripple, ensuring a smoother DC output. This combination of chokes and capacitors helps regulate the current and voltage, preventing excessive in-rush and ripple currents that could damage the circuit.
Additionally, choke circuit diagrams are valuable in troubleshooting and fault-finding. When a unit malfunctions, referring to the choke circuit diagram can help identify potential issues with the choke or power supply. By performing tests with a multimeter, one can verify the correct functioning of the choke and ensure it operates within the expected voltage range, typically between 12 and 14 volts AC or DC in many applications.
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Chokes vs inductors
A choke is a type of inductor, but its application, function, and design differ from other inductors. Chokes are designed to filter out certain frequencies or ranges of frequencies. They block higher-frequency alternating currents (AC) while passing direct currents (DC) and lower-frequency ACs. Chokes are commonly used in industrial, electrical, and telecommunications applications to remove or decrease noise and electromagnetic interference. They are also used in direct-current motor controllers to produce DC and remove voltage ripple (AC).
Inductors, on the other hand, have multiple functions, including storing energy in an electromagnetic field. They are passive electromagnetic components with two terminals used for inductance in a wide range of electronic equipment. Inductors can generate magnetic fields and store energy within them. They can also act as filters for adjusting impedance and as sensors that detect objects within the magnetic field. Inductors can step power up or down within a transformer and generate the rotation of a motor shaft.
While chokes and inductors share similarities and are both useful for improving circuit performance, they are not interchangeable. Chokes are specifically designed to block or filter certain frequencies, while inductors have a broader range of functions. Inductors designed for use as chokes are distinguished by not having the low-loss construction required in inductors used in tuned circuits and filtering applications.
The construction of chokes and inductors also differs. Chokes typically have a doughnut-shaped or toroidal core with an insulated wire coil wrapped around them. Inductors also have wire coils, but they can come in different shapes and sizes depending on the application. Some inductors, such as air core inductors, do not have a physical core.
In summary, while chokes and inductors are both essential components in electronic circuits, they differ in their specific functions, designs, and applications. Chokes are specialised for blocking or filtering frequencies, while inductors have a wider range of functions, including energy storage and power management.
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Frequently asked questions
A choke is an inductor used to block higher-frequency alternating currents (AC) while passing direct currents (DC) and lower-frequency ACs. They are typically made up of a coil of insulated wire wound on a magnetic, doughnut-shaped core.
Chokes are used to protect insulation from damage caused by steep rises in current in circuits by facilitating a gradual rise and fall of current. They also help break down voltage and can be used to filter out electrical noise and improve signal quality.
A CM choke is a type of choke that acts upon a common-mode signal. They are used to suppress electromagnetic interference (EMI) and radio frequency interference (RFI) on power supply lines, which can cause unwanted operation in electronic devices. They allow differential currents to pass while blocking signals that affect both wires.
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