As one of the basic passive components, inductors fill an important role in electronics applications, from starting engines to delivering power to your house. Inductors 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 is their physical size. Inductors often dwarf other electronic components in a circuit and add weight as well. Some techniques simulate a large inductor in a circuit. However, the added complexity and additional components limit where these techniques are used.
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 are central to 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. Some motorcycles and other vehicles don’t offer enough of a signature to be detected by the sensors without a 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. Transformers are found in many power supplies, to increase or decrease voltages to the desired level.
Because magnetic fields are created by a change in current, the faster the current changes (increase in frequency), the more effective a transformer operates. As the frequency of the input increases, the impedance of the inductor limits 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.
The gray canisters often found on the top of utility poles contain transformers.
Motors
Inductors are normally in a fixed position and aren’t allowed to move to align 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, making inductive motors robust and reliable.
Energy Storage
Like capacitors, inductors store energy. Unlike capacitors, inductors are limited on how long they can store energy because the energy is stored in a magnetic field, which collapses when power is removed.
Many simple electric motors that you’ll encounter, like those in fans, are inductive motors.
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 a transformer and an 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.
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