5 Applications of Inductors You Should Know

Inductors serve a variety of essential functions in electronic systems

As one of the basic passive components, inductors fill an important role in electronics applications, from starting engines to helping deliver power to your house. They store energy in a magnetic field when current flows through it; a typical inductor uses insulated wire wrapped into a coil around a central core.

As useful as inductors are, the biggest problem with using them is their physical size. Inductors often dwarf all other electronic components in a circuit and add a lot of weight as well. Some techniques simulate a large inductor in a circuit, but the added complexity and additional components limit where these techniques are used.

Close up of two copper inductors
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Filters

Inductors are used extensively with capacitors and resistors to create filters for analog circuits and in signal processing. Alone, an inductor functions as a low-pass filter, since the impedance of an inductor increases as the frequency of a signal increases.

When combined with a capacitor, whose impedance decreases as the frequency of a signal increases, a notched filter results that only allows a certain frequency range to pass through.

By combining capacitors, inductors, and resistors, advanced filter topologies support a variety of applications. Filters are used in most electronics, although capacitors are often used rather than inductors when possible, since they are smaller and cheaper.

Sensors

Contact-less sensors are prized for their reliability and ease of operation. Inductors sense magnetic fields or the presence of magnetically permeable material from a distance.

Inductive sensors lie at the heart of nearly every intersection with a traffic light that detects the amount of traffic and adjusts the signal accordingly. These sensors work exceptionally well for cars and trucks, but some motorcycles and other vehicles don't offer enough of a signature to be detected by the sensors without a little extra boost by adding an h3 magnet to the bottom of the vehicle.

Inductive sensors are limited in two major ways—either the object to be sensed must be magnetic and induce a current in the sensor or the sensor must be powered to detect the presence of materials that interact with a magnetic field. These parameters limit the applications of inductive sensors and influence the designs that use them.

Transformers

Combining inductors that have a shared magnetic path forms a transformer. The transformer is a fundamental component of national electrical grids, and they're found in many power supplies as well, to increase or decrease voltages to the desired level.

Those gray canisters often found on the top of telephone poles contain transformers.

Because magnetic fields are created by a change in current, the faster the current changes (increase in frequency) the more effective a transformer operates. Of course, as the frequency of the input increases, the impedance of the inductor begins to limit the effectiveness of a transformer. Practically, inductance-based transformers are limited to tens of kHz, usually lower. The benefit of a higher operating frequency is a smaller and lighter-weight transformer that delivers the same load.

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Motors

Normally inductors are in a fixed position and not allowed to move to align themselves with any nearby magnetic field. Inductive motors leverage the magnetic force applied to inductors to turn electrical energy into mechanical energy.

Inductive motors are designed so that a rotating magnetic field is created in time with an AC input. Since the speed of rotation is controlled by the input frequency, induction motors are often used in fixed-speed applications that can be powered directly from 50/60hz mains power. The biggest advantage of inductive motors over other designs is that no electrical contact is required between the rotor and the motor, which makes inductive motors very robust and reliable.

Many simple electric motors that you'll encounter, like those in fans are inductive motors.

Energy Storage

Like capacitors, inductors store energy. Unlike capacitors, inductors have a severe limitation on how long they can store energy because the energy is stored in a magnetic field which collapses when power is removed.

The main use for inductors as energy storage is in switch-mode power supplies, like the power supply in a PC. In the simpler, non-isolated switch-mode power supplies, a single inductor is used in place of transformer and energy storage component. In these circuits, the ratio of the time the inductor is powered to the time it is unpowered determines the input to output voltage ratio.