wiki:ControlSystems/Electrical/Training/Components/Inductors

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Inductors

An inductor is nothing more than a wire, usually coiled, often around a ferrous core material.

You already have a basic understanding of inductance from MS/HS physics:

  • Electrons flowing through a wire induce a magnetic field around it (how motors work)
  • A magnetic field moving around a wire induces a flow of electrons in it (how generators work)

The schematic (logical) symbol for an inductor is: Inductor schematic symbol

Some key things about inductors that will help you understand how they are used in circuits:

  • When you connect a power source to one side of an inductor, the voltage immediately appears at the output. However when you start to draw current (electrons) through the inductor, a magnetic field builds around the inductor before electrons start flowing through to the output. If current continues to flow, the magnetic field will eventually saturate and electrons will then flow unimpeded through the inductor (i.e. at that point it looks and behaves just like a wire with no inductance). During the time the magnetic field is building, the inductor impedes (resists) the increasing flow of current.
  • When the flow of current through an inductor decreases, the magnetic field collapses into the inductor, increasing the force on the electrons (raising the voltage and forcing electrons to flow) until the field has collapsed at which point the inductor again looks like a wire. During the time the magnetic field is collapsing, the inductor impedes (resists) the decreasing flow of current.
  • So there is a time-dependent aspect to the impedance of an inductor: it behaves differently as the magnetic field is building or collapsing than when the magnetic field is saturated or collapsed. The exact time-dependent behavior is easily understood with basic calculus but that is not necessary to understand how inductors are used. You can see the basic inductor equations here
  • It is also important to understand that inductors are complementary to capacitors. Capacitors also store energy but as charge rather than magnetic flux. Capacitors have a similar time-dependent impedance but impede changes in voltage rather than current. I.e. when a capacitor starts charging, the flow of current appears at its output immediately but the voltage across the capacitor rises slowly as the charge builds on the capacitor.
  • A popular mnemonic for this relationship is "ELI the ICE man": voltage leads current in inductors, current leads voltage in capacitors

In summary: inductors impede (resist) changes in current and capacitors impede changes in voltage. Both do so in a time-dependent way. The intuitive way to think about this is that inductors "try to maintain the same current flow" and capacitors "try to maintain the same voltage"

Additional reading related to inductors:

Last modified 6 months ago Last modified on Nov 27, 2020, 4:56:22 PM

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