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Inductor or Capacitor? Need help!!!

Discussion in 'General Electronics Discussion' started by jrd78ep, Mar 21, 2013.

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  1. jrd78ep

    jrd78ep

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    0
    Mar 21, 2013
    Hello i am new on this forum....i am troubleshooting an intrument...i found a mosfet with inductor (label L3) connects at drain and source...when i check the inductor it is fuse-open (read in Mohms). Wondering if it is really an inductor or not...because it is not normal to me to see inductor at drain & source...

    Any idea guys? thanks for the help. (PLEASE SEE ATTACHED FILE FOR THE PHOTO).
     

    Attached Files:

  2. Electrobrains

    Electrobrains

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    Jan 2, 2012
    Could be an SMD varistor to protect the MOSFET from voltage peaks.
     
  3. jrd78ep

    jrd78ep

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    Mar 21, 2013

    So you mean varistor also can be labeled "L3" ? thanks for the reply.
     
  4. Electrobrains

    Electrobrains

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    5
    Jan 2, 2012
    No, that would be very strange, but placing an inductor over Drain-Source of a MOSFET would be even stranger!

    It could happen in some rare oscillator circuits or the MOSFET could be used as a variable resistor to change the Q-factor of the inductor.

    Anyway, the component sure looks like an smd inductor.
     
  5. jrd78ep

    jrd78ep

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    Mar 21, 2013
    Now i'm getting confuse :-(
    Please help get a conclusion...since i measured it fuse-open and looks like smd inductor...do i need to replace it?

    Just to add up..this mosfet source pin is connected to ground. Thanks.
     
    Last edited: Mar 22, 2013
  6. Electrobrains

    Electrobrains

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    5
    Jan 2, 2012
    Well. some things in life are not so obvious, especially if we don't have a handbook...
    Maybe you have to analyze the circuit a bit more. What kind of instrument is it? What is the name of the MOSFET (cannot read it)? Where does the drain connect to? Can you get a circuit diagram from the manufacturer?
     
  7. jrd78ep

    jrd78ep

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    Mar 21, 2013
    Yes you're right...so i drawn the schematic to give better insight...please see attached file....hoping u can share now exact idea....thanks alot.
     

    Attached Files:

  8. Electrobrains

    Electrobrains

    259
    5
    Jan 2, 2012
    Seeing that schematic, it's most probably a protection component. The varistor alternative definitely got support.
    What is the name of the MOSFET?
     
  9. jrd78ep

    jrd78ep

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    Mar 21, 2013
    The mosfet is L540NS....thanks
     
  10. jrd78ep

    jrd78ep

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    0
    Mar 21, 2013
    Any update from you today Electrobrains??? I had sent u already the mosfet number....thanks
     
  11. Electrobrains

    Electrobrains

    259
    5
    Jan 2, 2012
    Probably it's an IRL540NS, a rough power MOSFET.
    What is the problem? What doesn't work in your "instrument"?
    Does the output not switch?
     
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