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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
     
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