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Inductors |
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 Inductors are closely related to capacitors; the rate of current change in an inductor depends on the voltage applied across it, whereas the rate of voltage change in a capacitor depends on the current through it. The symbol and defining equation for an inductor is where L is called the inductance and is measured in henrys (or mH, uH, etc.) and "di/dt" is the change in current over a small period of time. Putting a voltage across an inductor causes the current to rise as a ramp (for a capacitor), supplying a constant current causes the voltage to rise as a ramp; 1 volt across 1 henry produces a current that increases at 1 amp per second) The symbol for an inductor looks like a coil of wire; that's because, in its simplest form, that's all it is. Variations include coils wound on various core materials, the most popular being iron (or iron alloys, laminations, or powder) and ferrite, a black, nonconductive, brittle magnetic material. these are all ploys to multiply the inductance of a given coil by the "permeability" of the core material. The core may be in the shape of a rod, a toroid (doughnut), or even more bizarre shapes, such as a "pot core" Inductors find heavy use in radio frequency (RF) circuits, serving as RF "chokes" and as parts of tuned circuits. A pair of closely coupled inductors form the interesting object known as a transformer. An inductor is, in a real sense, the opposite of a capacitor. Arising from Faraday's law, the inductance L may be defined in terms of the emf generated to oppose a given change in current:
Every conductor has inductance, even though the conductor may not have been designed as an inductor. Inductance in any circuit is the property that opposes any change in the existing current. The unit of inductance may be stated in henrys, millihenrys, or microhenrys.When an alternationg voltage is applied to an inductance, a back electromotive force (emf) is generated in the inductance. This emf is proportional to the rat at which the
current changes -- The more rapid the change, the greater the back emf developed. And this, in turn, is proportional to the frequency of the alternating voltage.This opposition to the flow of alternating current is called inductive reactance, symbolized by XL. |
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In the real world inductors come in all shapes and sizes, like any other component.
Depending on the application these components can have a wide range of inductances. The smaller values tend to be applied to radio frequency tuned circuits while the larger can be used for EMI
(electromagnetic interference) suppression. i.e. high frequency filters commonly referred to as RF Chokes. Sometimes these chokes can be required to operate on high current power supplies. In these cases the coil windings can have large gauge wire windings and require significant pieces of ferrite core material to form the core.