Inductors

Discussion in 'Homework Help' started by KCHARROIS, Jul 10, 2012.

  1. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Hello, I'm looking at inductors and I've notice some look like resistors, some with ferrite cores or some with just coils of copper with air core. Does it matter which one you use like say for an oscillator? Or do they all do the same thing?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    They all have different values of inductances.
    Air core coils have very low inductances and are used in RF circuits.
    Inductors looking like resistors are your typical inductors for general purpose use.
    Ferrite beads are used for power supply filters to reject high frequencies.
     
  3. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
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    So what would you recommend for an oscillator circuit?
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    Depends on your frequency.
     
  5. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
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    Frequency I wish to achieve is 2 Mhz.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Next you have to show your circuit.
     
  7. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
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    Here's the circuit
     
  8. KCHARROIS

    Thread Starter Member

    Jun 29, 2012
    292
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    Sorry this pic is bigger
     
  9. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    It's a Colpitts oscillator. RF chokes would be fine - you may need to adjust something (capacitors say) to obtain the 2Mhz.

    C1=C2=6.2nF say
     
    Last edited: Jul 10, 2012
  10. OscGuru

    New Member

    Apr 3, 2012
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    An important thing to remember is that inductors have parallel capacitance which is distributed between coils and or the package capacitance. This parallel capacitance will resonate with the inductor inductance to give you a, parallel, high impedance resonance. This frequency is called the SRF, self resonance frequency. If you want to have a desired inductance at a given frequency make sure you use a an inductor that has a much higher SRF than your use frequency. The parallel capacitance will force the effective inductance to increase in frequency to SRF then above that point it looks like capacitor. RF chokes are inductors used above their SRF and behave as low value capacitors.
     
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