Inductor - Wikipedia
The inductor is one of the ideal circuit elements. Let's put an inductor's current- voltage equations to work and learn more about how an inductor behaves. (An “constitutive equation” is the equation that describes the relationship between the element voltage and element current.) Capacitors and inductors are . In electromagnetism and electronics, inductance is the property of an electrical conductor by . If the current is increasing, the voltage is positive at the end of the conductor through which the current enters and . the constant inductance equation above is only valid for linear regions of the magnetic flux, at currents below the.
But what does negative power mean? It means that the inductor is releasing power back to the circuit, while a positive power means that it is absorbing power from the circuit. Since the positive and negative power cycles are equal in magnitude and duration over time, the inductor releases just as much power back to the circuit as it absorbs over the span of a complete cycle. What this means in a practical sense is that the reactance of an inductor dissipates a net energy of zero, quite unlike the resistance of a resistor, which dissipates energy in the form of heat.
Mind you, this is for perfect inductors only, which have no wire resistance. This opposition to alternating current is similar to resistance but different in that it always results in a phase shift between current and voltage, and it dissipates zero power. Because of the differences, it has a different name: Reactance to AC is expressed in ohms, just like resistance is, except that its mathematical symbol is X instead of R. To be specific, reactance associated with an inductor is usually symbolized by the capital letter X with a letter L as a subscript, like this: Since inductors drop voltage in proportion to the rate of current change, they will drop more voltage for faster-changing currents, and less voltage for slower-changing currents.
However, the small dimensions limit the inductance, and it is far more common to use a circuit called a gyrator that uses a capacitor and active components to behave similarly to an inductor.
Regardless of the design, because of the low inductances and low power dissipation on-die inductors allow, they're currently only commercially used for high frequency RF circuits.
Shielded inductors[ edit ] Inductors used in power regulation systems, lighting, and other systems that require low-noise operating conditions, are often partially or fully shielded. Air-core inductor[ edit ] An antenna tuning coil at an AM radio station.
It illustrates high power high Q construction: The term air core coil describes an inductor that does not use a magnetic core made of a ferromagnetic material. The term refers to coils wound on plastic, ceramic, or other nonmagnetic forms, as well as those that have only air inside the windings. Air core coils have lower inductance than ferromagnetic core coils, but are often used at high frequencies because they are free from energy losses called core losses that occur in ferromagnetic cores, which increase with frequency.
Inductor i-v equation in action (article) | Khan Academy
A side effect that can occur in air core coils in which the winding is not rigidly supported on a form is 'microphony': Radio-frequency inductor[ edit ] Collection of RF inductors, showing techniques to reduce losses. The three top left and the ferrite loopstick or rod antenna,     bottom, have basket windings.
- Inductors and Calculus
- Inductor i-v equation in action
At high frequenciesparticularly radio frequencies RFinductors have higher resistance and other losses. In addition to causing power loss, in resonant circuits this can reduce the Q factor of the circuit, broadening the bandwidth. In RF inductors, which are mostly air core types, specialized construction techniques are used to minimize these losses.
The losses are due to these effects: Skin effect The resistance of a wire to high frequency current is higher than its resistance to direct current because of skin effect. Radio frequency alternating current does not penetrate far into the body of a conductor but travels along its surface.
Therefore, in a solid wire, the interior portion of the wire may carry little current, effectively increasing its resistance. Proximity effect Another similar effect that also increases the resistance of the wire at high frequencies is proximity effect, which occurs in parallel wires that lie close to each other. The individual magnetic field of adjacent turns induces eddy currents in the wire of the coil, which causes the current in the conductor to be concentrated in a thin strip on the side near the adjacent wire.
Like skin effect, this reduces the effective cross-sectional area of the wire conducting current, increasing its resistance. Dielectric losses The high frequency electric field near the conductors in a tank coil can cause the motion of polar molecules in nearby insulating materials, dissipating energy as heat. So coils used for tuned circuits are often not wound on coil forms but are suspended in air, supported by narrow plastic or ceramic strips.
AC Inductor Circuits
Parasitic capacitance The capacitance between individual wire turns of the coil, called parasitic capacitancedoes not cause energy losses but can change the behavior of the coil. Each turn of the coil is at a slightly different potential, so the electric field between neighboring turns stores charge on the wire, so the coil acts as if it has a capacitor in parallel with it.
At a high enough frequency this capacitance can resonate with the inductance of the coil forming a tuned circuitcausing the coil to become self-resonant. High Q tank coil in a shortwave transmitter left Spiderweb coil right Adjustable ferrite slug-tuned RF coil with basketweave winding and litz wire To reduce parasitic capacitance and proximity effect, high Q RF coils are constructed to avoid having many turns lying close together, parallel to one another. The windings of RF coils are often limited to a single layer, and the turns are spaced apart.
To reduce resistance due to skin effect, in high-power inductors such as those used in transmitters the windings are sometimes made of a metal strip or tubing which has a larger surface area, and the surface is silver-plated. How much voltage the inductor will produce depends, of course, on how rapidly the current through it is decreased. With a decreasing current, the voltage polarity will be oriented so as to try to keep the current at its former magnitude.
In this scenario, the inductor will be acting as a source, with the negative side of the induced voltage on the end where electrons are exiting, and the positive side of the induced voltage on the end where electrons are entering.
The more rapidly current is decreased, the more voltage will be produced by the inductor, in its release of stored energy to try to keep current constant. Again, the amount of voltage across a perfect inductor is directly proportional to the rate of current change through it.
The only difference between the effects of a decreasing current and an increasing current is the polarity of the induced voltage. For the same rate of current change over time, either increasing or decreasing, the voltage magnitude volts will be the same. If current through an inductor is forced to change very rapidly, very high voltages will be produced. Consider the following circuit: In this circuit, a lamp is connected across the terminals of an inductor. A switch is used to control current in the circuit, and power is supplied by a 6 volt battery.