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What is the purpose and application for inductors?

  1. Jan 14, 2013 #1
    After (partially) completing my goal of understanding capacitors, I'm onto inductors, even after reading the wiki article and doing a little more research, they make no sense to me. Currently what I'm thinking is that they are the "opposite" of capacitors, allowing DC to pass through but blocking AC. Is this true?
    If not, what do they do?
    And while I'm at it, one more: How do they work?
  2. jcsd
  3. Jan 14, 2013 #2


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    If that were true then transformers wouldnt work ;)

    transformers are just 2 inductors side by side

  4. Jan 14, 2013 #3


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    how about referring to specific parts of the wiki article that you dont understand
    and people here will be able to help you :)

  5. Jan 14, 2013 #4


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    iductors do complement capacitors when you're talking about ac at different frequencies.
  6. Jan 14, 2013 #5
    I'll try to find it again when I get on my computer. From what I remember it didn't say anything about their use, just the parts and how it was assembled. It said 'an inductor generates a magnetic field when current passes through it', I don't see what use that has in the way I see them put into circuits.
  7. Jan 15, 2013 #6


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    hi ya
    yes show us some specific examples of inductors in circuits that you dont understand their use.

    As I said earlier, transformers are very common uses of inductors, for stepping up and down AC voltages. Your can also use transformers where the number of turns of wire is the same on the primary as on the secondary. This is called a 1:1 transformer and are often used in audio circuits to provide isolation between different stages of a circuit.

    BUT just backing up for a moment .... and clarifying a comment you made....

    now just in case you didnt realise, an inductor DOESNT have to be a coil and NOT just a coil generates a magnetic field. EVERY piece of wire or a copper track on PCB that has a current flowing through it produces a magnetic field regardless of if it is coiled or straight.
    What the coil does is increases the inductance and it concentrates the magnetic field into a confined area...
    Classic example .... an electro-magnet, found in relays and solenoids or the huge electro-magnet on the end of the crane cable at the local scrap metal yard.

    In the RF ( Radio Frequency) electronics field where I do most of my professional work and amateur radio experimenting. Particularly at higher frequencies, say above 1 GHz, the inductance of short circuit tracks and lengths of wire can pose real problems that have to be taken into account when designing a circuit layout.
    There are some places in a circuit that we want inductance to occur, in other areas we dont.

    OK some circuit examples ....
    a basic tuned circuit ... an inductor in parallel with a capacitor along with a detector diode and you have a radio receiver...


    in this circuit below from my VHF (144MHz) transceiver radio I did a modification so I could inject 12VDC into the coax cable to power a preamplifier up at the antenna.


    You can see a number of inductors in this circuit ... L1, 2, 3 and the associated capacitors are filtering of the output to stop harmonics of 144MHz from being radiated.
    L6, I added, this inductor will pass the 12V DC, but because of its value, will block the 144MHz transmitted signal from getting into the 12VDC power supply
    This is a common use of inductors in RF circuits, these type of inductors are called RF Chokes

    there's some uses for you to ponder on. Electronics wouldnt be what it is without inductors


    Attached Files:

    Last edited: Jan 15, 2013
  8. Jan 15, 2013 #7
    Personally - I always try to keep in mind how Inductors and Capacitors are analogs - both store energy, the capacitor in an electric field - and an inductor in a magnetic field. Behavior of a Capacitor relative to Voltage and Current - are the same as an Inductor relative to Current and Voltage - note the reversals.
  9. Jan 15, 2013 #8
    Inductors are used in SMPS (Switched Mode Power Supplies), which means your laptop-, computer-, tv-, tablet- and phonecharger.

    DC-DC switching converters are the most widely used power supply, and they need inductors to work :)
  10. Jan 15, 2013 #9
  11. Jan 16, 2013 #10


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    the inductor L1 along with the capacitor C2 form a ripple filter

    if the inductor wasnt there, there would not be any ripple filtering and the ~ 150kHz typical switching freq of the chip would appear on the output supply to the load.

    The last thing you would want in your audio, RF or digital circuitry is to have a 150kHz signal imposed on the signals you were working with.

  12. Jan 16, 2013 #11
    Alright, I think I've almost got it.
    Thanks for the help guys.
  13. Jan 16, 2013 #12
    Sorry to further confuse the issue - but note that the inductor in a Boost SMPS supply - is required - not really a filter. The V=L* dI/dt.

    I also happend across this : http://www.coe.montana.edu/ee/rmaher/EELE250/EELE%20250_09a.pdf [Broken]

    So the capacitors will help reduce voltage ripple and inductor reduce current ripple.
    Last edited by a moderator: May 6, 2017
  14. Jan 16, 2013 #13
    Page 8, no current will pass through the inductor? Why is that? If it's a DC source the current isn't changing.
  15. Jan 16, 2013 #14


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    the datasheet calls it a ripple filter along with the cap :)

    Last edited by a moderator: May 6, 2017
  16. Jan 17, 2013 #15
    My comment was about a BOOST vs the BUCK supply. You can make a buck with no inductor ( but not a good one) but a Boost requires the inductor.
  17. Jan 20, 2013 #16
    Transformer are NOT just 2 inductors side by side !!!
  18. Jan 20, 2013 #17


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    ohhh really ?

    they can be Transformers comer in a variety of styles
    side by side coils, intertwined coils, cored, un cored some examples :)
    but, from a basic concept, just 2 coils side by side

    so what is the point you are trying to make?, clarify your statement :)

    Last edited: Jan 20, 2013
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