Inductive Components
(1 125)Rapid changes in electrical current are an extremely dangerous phenomenon that can damage the printed circuit board of an electronic system. In order to effectively protect the system against electrical current interference, suppression chokes are used. They are an extremely important component of electrotechnical and electronic systems, which should be known by every professional.
Choke design
Despite the crucial role of chokes, their design is extremely simple. A wire of appropriate thickness, formed into a spiral shape, is the basic element. The most common solution is to wind the spiral on a core made of ferromagnetic material with strong magnetic properties (e.g. cobalt, nickel or commonly used iron). Another, less commonly used design is the air-core choke, i.e. filling the coil with air. However, the disadvantage of the latter solution is that the coiled wire needs to be properly reinforced in order to prevent unwinding, as well as lower inductance in relation to chokes with cores (with the same number of coils). The use of core makes it possible to adjust choke inductance by changing its position in relation to the surrounding coils. Depending on operating conditions and application, we distinguish between designs equipped with a closed magnetic circuit, i.e. so-called shielded chokes, and those with an open magnetic circuit.
The application and installation method require using various types of passive elements with different shapes and types of wire winding. The most commonly used types of chokes are presented below:
- SMD chokes;
- THT chokes;
- DMF current-compensated chokes.
How does the choke work?
A choke prevents sudden changes in current due to the magnetic field created around a live conductor. When the intensity of the flowing electric current changes abruptly, the magnetic field also changes, which nullifies the undesirable phenomenon by reverse currents. This so-called current throttling is also called self-induction and increases proportionally to the changes in the flowing current.
The most important parameter of a choke is its inductance, which in fact speaks about its ability to generate a magnetic field producing reverse current. In order to select the right choke, its resistance and allowable operating current must also be taken into account. Another parameter describing the properties of the coil is the Q factor. It determines the ability to throttle flows with frequencies deviating from its own resonant frequency.
The unit that characterizes a coil is Henry [H]. It tells you that a change in current of 1 ampere per second induces a voltage of 1 volt.
The increase in the inductance of a coil can be influenced by:
- Increasing the number of coils and their surface area;
- Selecting suitable material for the core structure, with high relative permeability;
- Shortening coil length.
The use of chokes and their function
Devices that use the discussed induction elements surround us everywhere. Therefore, it is worth knowing where we can find them. Here are some examples:
- Drive systems equipped with inverters – filtering of interference resulting from motor speed control with the use of a frequency converter;
- All types of loudspeakers – a choke acting as an anti-interference device significantly improves the acoustic qualities of the generated sound;
- Capacitive batteries – chokes as protective elements for capacitors
Standard coil versus choke – basic differences
Chokes are included in the group of inductors. For this reason, the terms choke and coil have been used interchangeably. At this point, however, it should be noted that not every coil is a choke. These elements are distinguished primarily by the way they are used in the electrical system. A coil is a choke only if its task is to prevent an undesirable change in current intensity. A different application of a coil (e.g. in electromagnets as a source of attracting metal elements) means that this element cannot be classified as a choke.
Power loss in the coils
The main reason for power loss in the coils is the resistance of the winding wire. Because of this, the coil heats up and the magnetic properties of the core change. It is especially dangerous in the case of high currents, as it may damage electronic components and, consequently, lead to a failure of the entire system.
Another important detail is precise workmanship. Careful winding of the wire or appropriate gaps between subsequent coils have a fundamental impact on the quality of the generated magnetic field. Its dispersion leads to a measurable loss of the choke's efficiency. It is worth mentioning that a poorly made coil may generate additional heat, which increases the risk of overheating the circuit as described above.
The quality of the core itself also has a huge impact on the power loss. Uneven implementation of the core can lead to generating large deviations of the actual parameters in relation to the nominal values.
Chokes – how to select the right one?
To sum up, chokes are used in devices that require suppression of sudden changes in currents, signal filtering or protection against overloads caused by harmonic currents. Due to the very wide application and parameters specific to each coil, special attention should be paid to selecting the appropriate circuit element. Only a choke with an appropriate inductance and designed to work with a specific current intensity can meet the requirements. Therefore, choosing such important elements of an electronic circuit should not be guided solely by economic aspects. It is worth relying on products from proven manufacturers that will meet the quality requirements and allow for long-term, failure-free operation.
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