What is a chokes?

A choke is a low-impedance coil used to attenuate high-frequency currents in a circuit. Choke coils are used in the power supply of electronic equipment and electrical appliances, power electronic equipment and high-frequency equipment. In order to improve its inductance, the choke coil usually has an iron core made of soft magnetic material.

Ring Choke

Toroidal core chokes have a ferrite or powdered toroidal core. The annular core can also be composed of crystalline or amorphous metal ribbons. This ring-shaped core forms a complete magnetic circuit, so it has only a small diffuse magnetic field. This improves electromagnetic compatibility and also improves coupling due to small losses in the magnetic field. Extreme toroidal chokes are ferrite beads that wrap around a wire.

Rod Core Choke Coil

The magnetic circuit of the rod core choke is open. But they can withstand relatively strong magnetic strength, if they are just wrapped in a layer of wire, their capacitance is relatively small, so they are suitable for very high frequency circuits. Rod core choke coils in high frequency circuits use ferrite, and electric paper is used as the core in power supplies.

Air Core Choke Coil

Air core choke coils are used in very high frequency technology. The core of such a choke has no ferrite, so it has no magnetic saturation, no losses due to eddy currents and hysteresis. But it requires more coils to achieve the same inductance than iron or ferrite chokes. This means that its resistance is relatively high.

iron core

Most choke coils have a ferromagnetic core, and such choke coils can achieve the same inductance using far fewer coils than air core choke coils. But if the current is too strong, the iron core will be saturated, the inductance will be reduced a lot at this time, and the current will also be abnormal. In addition, if alternating current flows through the coil, eddy currents will appear in the iron core. In order to reduce eddy currents, the conductive substances in the core must be isolated from each other. In a transformer, the core is composed of multiple layers of isolated iron plates along the magnetic field, or the core is even composed of ferromagnetic powder.

Ferrite materials are non-conductive, but ferromagnetic, so ferrite core chokes have no eddy current losses and can be used in very high frequency circuits. At high currents, ferrite tends to saturate due to its lower saturation inductance than other materials. It can be prevented from reaching saturation by using a core with an open magnetic circuit or by leaving a gap in the core.

Suppression Choke

The role of choke coils is to have little or no effect on DC and low frequency currents, but effectively suppress high frequency AC currents through their high inductance. The purpose is to reduce high frequency radiation. Since all the current in the circuits behind them flows through the choke coils, their wires are generally thicker to reduce resistive losses.

The choke coil for interference cancellation needs to have high impedance over the widest possible frequency band. Therefore they need to have high inductance and at the same time low capacitance. This requirement is often not met by a single shape, and many combine multiple choke coils with different properties.

Common Mode Choke Coil

Common mode choke coils have multiple identical coils in which current flows in opposite directions, so the magnetic field cancels out in the core of the choke coil. Common mode choke coils are often used to suppress interference radiation, because such interference currents are reversed in different coils. The inductance of the common mode choke is very high for such currents. Common mode choke coils are often placed at the inlet and outlet of switching power supplies and power filters.

A particularly simple type of common mode choke is to run wires through a ferrite toroid, but they suppress interference only at very high frequencies (VHF). This tiny common-mode choke is used at the I/O bus and at the entrance of switching power supplies. Such chokes come in a variety of forms, woven, cylindrical or flat, and ferrite cores that can be split.

Common mode chokes cannot suppress touch interference. In practice, touch interference can be reduced by cleverly arranging common mode chokes by exploiting their inherent inductance.

Common mode chokes often consist of a one-piece, annular ferrite core, E-shape or D-shape [1]. The wire is wound around the core. Winding each coil around multiple cavities reduces capacitance and increases its resonant and effect frequencies.

Ballast

Gas discharge tubes require a ballast, which typically contains a choke coil. Through its virtual resistance it can effectively limit the current intensity, through the help of a starting current it can supply the high voltage required to turn on the fluorescent lamp.

The choke coil in the traditional ballast is made of an elect