A choke is a low-impedance coil

A choke is a low-impedance coil used to attenuate high-frequency currents in a circuit. Chokes are used in power supplies for electronic equipment and appliances, power electronics and high-frequency equipment. In order to improve its inductance choke usually has a core made of soft magnetic material.

Toroidal choke
The toroidal choke has a ferrite or powdered toroidal core. This annular core can also be composed of crystalline or amorphous metal bands. This toroidal core forms a complete magnetic circuit, so it has only a small dispersed magnetic field. This improves electromagnetic compatibility, as the loss of the magnetic field is small and the coupling is also improved. Extreme toroidal chokes are ferrite beads that surround electric wires.

Core choke
The magnetic circuit of the core choke is open. However, they can withstand relatively strong magnetic strength. If they are only wrapped with a layer of wire, their own capacitance is relatively small, so they are suitable for very high frequency circuits. The core chokes in high-frequency circuits use ferrites, and electric paper is used as the core in the power supply.

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

Iron core
Most chokes have a ferromagnetic core. Such chokes can use far fewer coils to achieve the same inductance than air-core chokes. But if the current is too strong, the core will saturate, the inductance will be reduced a lot, and the current will be abnormal. In addition, if alternating current flows through the coil, eddy currents will appear in the core. In order to reduce the eddy current, the conductive materials in the core must be isolated from each other. In the transformer, the core in the magnetic field direction is composed of multiple isolated iron plates, or the core is even composed of ferromagnetic powder.

The ferrite material is non-conductive, but has ferromagnetism, so the ferrite core choke has no eddy current loss and can be used in very high frequency circuits. At high currents, ferrites tend to saturate because they have lower saturation inductance than other materials. It can be prevented from reaching saturation by using an open magnetic core or by leaving a gap in the core.

Suppression choke
The role of chokes is to not affect or rarely affect DC and low-frequency currents, but effectively suppress high-frequency AC through their high inductance. The goal is to reduce high-frequency radiation. Because the current in all the circuits behind them flows through the choke, their wires are generally thicker to reduce resistance losses.

The choke for canceling interference needs to have a high impedance in the widest possible frequency band. Therefore they need to have high inductance and low capacitance at the same time. This requirement can often not be achieved by one shape, and many chokes with different performances are combined.
Common mode choke
The common mode choke has multiple identical coils, and the current flows in these coils in the opposite direction, so the magnetic field is canceled in the core of the choke. Common-mode chokes are often used to suppress interference radiation because such interference currents are reversed in different coils. The inductance of such a common mode choke is very high. Common mode chokes are often placed at the entrance and exit of switching power supplies and power filters.
A particularly simple common-mode choke coil is to let the wires pass through the ferrite core, but they only suppress interference at very high frequencies (very high frequencies). This tiny common-mode choke is used at the entrance of the I / O bus and switching power supply. Such chokes come in various forms, either woven, cylindrical or flat, or ferrite cores that can be separated.
Common mode chokes cannot suppress touch interference. In practice, interference can be reduced by cleverly arranging common mode chokes using their inherent inductance.
Common mode chokes often consist of a single, ring-shaped ferrite core, E-shaped or D-shaped [1]. The wire is wound around the core. Winding each coil around multiple cavities can reduce capacitance and increase its resonance and effect frequencies.

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