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I to v converter

  1. Feb 7, 2016 #1
    Hi all,
    I need to convert i to v using photodiode and iv converter, now the photodiode can give reverse light current upto micro amps and to convert it to volt i am using opamp with has max input bias current of about nano amps , now how can i convert this micro amps to nano amps because it should not destroy my opamp , can you please suggest a current limiter circuit so that my voltage remains the same
     
    Last edited by a moderator: Feb 7, 2016
  2. jcsd
  3. Feb 7, 2016 #2

    LvW

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    I am afraid, you are confused regarding the currents.
    It is the INPUT current into the opamp which is in the nano-ampere range.
    Hower, this can be neglected using an opamp in the classical I-V converter arrangement.
    Do you know how such a circuit (with feedback) looks like?
     
  4. Feb 7, 2016 #3
    Y
    Yeah, but i am using an inverting ckt theonly issue is regarding e currentthat into the inv terminal , will current in microamps damage the opamp
     
  5. Feb 7, 2016 #4

    LvW

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    No - the current enters the feedback resistor.
     
  6. Feb 7, 2016 #5
    Oh thanks... Just got that thanks.. Thank you sir
     
    Last edited by a moderator: Feb 7, 2016
  7. Feb 7, 2016 #6
    Ok so the current goes via feedback and maintains a voltage level vo and keeps non inv at thesame level... So it does not goto inverting terminal... Right,, sir
     
  8. Feb 7, 2016 #7

    CWatters

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    Can I suggest you post your circuit diagram.
     
  9. Feb 7, 2016 #8
    I agree with CWatters, it's awkward to give a useful answer without knowing which components you are using and where they sit in your circuit.

    I think, if you are using an appropriate op-amp for your purpose, the bigger concern would be in handling noise to get a useful response from your monitor.
     
  10. Feb 7, 2016 #9
  11. Feb 7, 2016 #10
    Please find the circuit attached above
     
  12. Feb 8, 2016 #11

    berkeman

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    The circuit schematic you posted does not use a photodiode...
     
  13. Feb 8, 2016 #12
    Well i used an ldristead of photodiode to illustrate that, since my simulator didnt have the phtodiode
     
  14. Feb 8, 2016 #13

    berkeman

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    That's a completely different circuit than the one you were asking about. Just find an example circuit using Google Images and post that instead so we can discuss it. :smile:
     
  15. Feb 8, 2016 #14

    berkeman

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  16. Feb 8, 2016 #15
    Thank you sir
     
  17. Feb 8, 2016 #16

    berkeman

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    You are welcome, but you didn't answer my question. I understand that the language translation issue is a problem, but we should still be able to help you if you would ask a clear question based on that simplified schematic. :smile:
     
  18. Feb 8, 2016 #17

    rbelli1

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    You can also use the schematic berkeman posted with an LED however the output will likely be lower than a purpose built photodiode. Single supply operation is possible if you apply an appropriate voltage to the non-inverting input.

    BoB
     
  19. Feb 8, 2016 #18
    Well,my issue was the current entering into the the inverting terminal of opamp exceeding the specified limit, but later on found out that most of the current went thro the feedback R , and the current entering invl was only nano amps
     
  20. Feb 8, 2016 #19

    rbelli1

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    For voltage feedback op amps you don't want to rely on the exact value of the input bias current as this is a parasitic. You want to design your circuit so that the bias current is either insignificant or you compensate for it somehow.

    BoB
     
  21. Feb 8, 2016 #20

    davenn

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    That's correct, you have discovered a main rule of Op-Amp circuits
    In an ideal/near idea situation no current flows into or out of the inputs of an op-amp

    have a look at this great video from Dave @ EEV-blog

    http://www.bing.com/videos/search?q...950D0C45487CFCBDAEFE950D0C45487CFC&FORM=VIRE1


    I have posted this link a number of times over the years :smile:
    cheers
    Dave
     
  22. Feb 9, 2016 #21

    CWatters

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    I think you misunderstand this parameter. Its not a limit you must comply with. Its a limit that the manufacturer of the op amp has designed it to achieve. Eg the op amp is guaranteed not to let more than this much current flow into the inputs.
     
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