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Inductors, how and why ?

Discussion in 'Electronic Basics' started by Saad, Apr 3, 2004.

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  1. Saad

    Saad Guest

    Hi there !
    I am posting this message to ask that is there anything else we can
    use in place of inductors in a circuit and how do we determine the
    value of a capacitor or inductor in a circuit and i can't find
    inductors physically....where do i find them ? Please answer my
    queries soon.
  2. Without changing the design of a circuit, there is no equivalent part
    for inductors. They have unique properties.

    Most capacitors are marked with a code for their value. See:
    Lots of good info on capacitors:

    Inductors are often made custom and often have no markings that tell
    you their values, though there are some standards for some forms:

    The neat thing about inductors is that they are the one component you
    may be able to make as good as those you can buy.

    I don't know what country you live in, but Digikey now carries quite a
    line of inductors available in the U.S. and Canada.
    Enter inductor in the search box.
  3. Whether one can do without an inductor would depend on what's needed.

    Gyrators (using op-amps to synthesize inductors) have seen use at
    audio frequencies, where the inductors would be way too bulky for
    many applications. But, it's not a perfect replacement, so it can't
    be used for every inductor, and it can't be used as a direct replacement.

    What you're more likely to see is using circuits that replace the
    function of a circuit that requires an inductor, with a circuit that
    does the same thing without inductors.

    For instance, active filters have become quite popular, again at
    audio. They are substituting a complete stage that filters for
    some sort of filter that uses an inductor.

    One would see a switch from an oscillator that requires an inductor
    to an oscillator that uses resistors and capacitors as the frequency
    determining element.

    A lot of IC designs may use more complicated circuitry because it
    does away with inductors, which can't be done in ICs, and might dwarf
    the IC when external. One example of this would be the NE567 tone
    decoder IC, that is over thirty years old now. It uses a phase locked
    loop and some additional circuitry to detect when a given frequency is
    present at the input. The IC has multiple stages of multiple active
    elements, and would be terribly cumbersome with discrete transistors,
    but it all fits into an 8-pin IC. Before that, one would tend to see
    bulky inductors and relatively large capacitors to provide a filter
    to detect a given frequency, and it wasn't nearly as tuneable.

    There was a time when inductors were often used in order to get
    needed gain out of a stage, rather than to provide real selectivity.
    With ICs, there was so much gain available that one could do away with
    such inductors, and broadband to boot.

    At radio frequencies, some filters went from inductor based to
    ceramic and crystal filters. They come to you as black boxes,
    and require no tuning. Before they came along, one would require
    multiple inductors to provide the same selectivity.

  4. Tim Auton

    Tim Auton Guest

    I'm not sure what you're trying to do (design a circuit, understand an
    existing circuit etc.), but if you're looking at an existing circuit
    trying to see where the inductor is then be aware that they aren't all
    obvious. For example, in this circuit:

    the inductor is the green thing in the middle that looks like it could
    easily be something else.

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