simple amp for phototransistor

Discussion in 'The Projects Forum' started by burtS, Feb 25, 2011.

  1. burtS

    Thread Starter Member

    Mar 6, 2008
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    Am using a phototransistor (2 leads) to detect a photobeam break in an otherwise 24vdc system. Output signal from the photocell amp goes to the input of an ACCES digital DIO interface which requires 3-30 v ac or dc. For several reasons I use a dc for the input to the interface and want it to be negative.

    Came up with the attached circuit which works and appears stable but is probably not optimal and would be pleased to receive feedback/suggestions/simple alternatives, etc.
    Burt
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. hgmjr

    Moderator

    Jan 28, 2005
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    Another approach for your consideration would be the use of a current mirror similar to the approach shown in this post. Of course you would replace the photodiode with your photo-transistor.

    hgmjr
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Are you saying you want the DIO interface input to be 0V when the phototransistor is not illuminated, and -24V when it is?
     
  5. burtS

    Thread Starter Member

    Mar 6, 2008
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    YES or at least less than 3v
     
  6. burtS

    Thread Starter Member

    Mar 6, 2008
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    Sorry, did not address both questions: Yes, less than 3 v and, when interrupted, any where between -4 and -24 v. The circuit I'm using works but I assume there is a better and (hopefully) equally simple solution.
    Thanks,
    Burt
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    How much current does your IO require? Can you link to a datasheet of the ACCES digital DIO interface?
    Also, link to a datasheet of your phototransistor.
     
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