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      • Published 12 Jun 2023
      • Last Modified 29 Aug 2023
    • 6 min

    How Do Inductors Work?

    Find out more about the role inductors play in electronic circuits.

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    Reviewed by Karl Ralph, Technical Support Engineer (November 2022)

    Inductors are helpful electrical components that work passively to stop any magnetic flux from causing problems in a circuit. Typically made from an insulated wire that’s coiled up, inductors are also known as coils, chokes or reactors and work by temporarily storing electrical energy in part of a circuit and preventing any sudden surges or spikes.

    Depending on the specific needs of a circuit, inductors with particular properties will be required to ensure they can cope with the demands of the energy that will pass through it. Properties that vary between inductors and that influence their capacity include the type of material they’re made from, the number and spacing of coils and the length of the inductor itself.

    What Do Inductors Do in Circuits?

    Inductors are designed to slow down the flow of an electrical current through a circuit. Their coiled design makes this possible. This is because, as an electrical current flows through the wire, the coil generates a magnetic field around it. This magnetic field builds up and is stored to its maximum size as the current continues to flow.

    Then, when the current is switched off, this field will collapse, be converted into electrical energy, and pass some electrons along the wire. This means there aren’t sudden surges or drops in electrical energy that could cause problems to components (e.g., a light bulb or fan) within the circuit or disrupt the circuit’s function.

    How Inductors Work in a Circuit

    It’s worth noting that inductors will work differently in an AC circuit compared to a DC circuit. The current in a DC circuit is constant. This means that, when a DC circuit with an inductor in it is first turned on, the inductor’s resistance is at its maximum, as it will oppose the direct flow of electricity between the two poles. Over time, this resistance will drop until there is zero resistance, meaning the inductor acts just like another piece of wire.

    In contrast, the changes in polarity (frequency) in an AC circuit mean that the inductor’s performance adapts based on this flow. This often means that certain frequencies of AC current will pass through the inductor and others won’t, a feature that has been used to great effect in choke inductors which resist certain frequencies of AC while allowing others, along with DC current, to pass through.

    Inductor Circuit Symbol

    When designing a circuit, inductors will be indicated by a symbol.

    Inductor Circuit Symbol

    Depending on the specific design of the coil, such as the type of core used in the wire, there may be lines passing through the centre of this symbol.

    Inductor Circuit Symbol

    There may also be an ‘L’ above the symbol, which indicates the level of inductance, or the ability of an inductor to store energy, in the inductor.

    What are Inductors Used for?

    Depending on the needs of a circuit, electricians may combine multiple inductors or alongside other components. This means inductors can be used in a circuit for:

    • Filtering certain frequencies: when combined with a capacitor, which resists more flow as the frequency of a current increases, inductors can be used to filter frequency ranges through a circuit
    • Sensing movement: if another magnetic field or object that disrupts the inductor’s magnetic field is sensed, then a circuit can be triggered. This makes inductors useful contactless sensors in a variety of applications e.g., automatic traffic lights
    • Transforming power: combining inductors allows a magnetic field to increase or decrease and cause a change in current, making them ideal transformers
    • Driving motors: by combining an inductor’s magnetic force with an AC current, a motor can be powered without any contact being made between the rotor and the motor, meaning they can function at a constant speed more reliably
    • Storing energy: inductors can store energy in a magnetic field for a short amount of time, which makes them useful for switch-mode power supplies that need to turn on or off at higher frequencies

    How to Read Inductors

    If you’re looking through an inductor kit to find the right option for your circuit, it’s important to double-check the numbers and colour markers on the component itself. Often, an inductor will have three digits on its surface. To work out the inductance in microhenries (uH), the first two digits should be multiplied by the third digit to the power of 10.

    For example, if the code said 233, the calculation would be:

    23 x 10^3 = 23,000 uH (23mH)

    If there’s the letter ‘R’ in between two digits, this indicates a decimal point. E.g., 7R2 = 7.2 uH. Another letter, such as u, n, or p, will indicate a different unit of inductance such as N equals nano-henry.

    Then, if there’s a fourth digit at the end of the code, this will indicate the tolerance of the inductor, with B equalling the lowest and N the highest. Plus, in some cases, there may be colour codes on the inductor rather than numbers and letters, with the first and second being the value number and the third indicating the multiplier you need to use to get the inductance value. If there’s a fourth, this will indicate the tolerance of the inductor by percentage. Checking a colour code chart will help you to find the final values.

    Though this code gives you the value of inductance (how much energy can be stored by the inductor) to measure its impedance (how much energy it is resisting), you then need to use the calculation below (where f is the frequency in Hertz of the current passing through the inductor and L is the component’s inductance in Henries).

    XL = 2πƒL

    What are Some of the Different Types of Inductors?

    Depending on the needs of your specific circuit, you may require a specialised type of inductor, such as:

    By making sure you have an inductor with the right level of impedance and inductance, know how to combine inductors with other components and choose the best design for your needs, you can ensure your circuit operates effectively and safely.

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