Photo-Transistor Circuit

Discussion in 'The Projects Forum' started by tritechinc, Dec 21, 2015.

  1. tritechinc

    Thread Starter New Member

    Dec 21, 2015
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    Has anyone ever seen a circuit like this before? The emitter is tied to VCC.

    Please note that the diode is a photo-diode, there is an emitter circuit but it is not shown. I am trying to copy a small circuit board from a defective IR receiver. There are no schematics and the company is long gone. I traced out the circuit paths and diode checked the transistor. I do not know the resistor value because that is what failed, I should be able to figure that out doing a little math. (The top blew off so I can not read the code, the entire thing is smt and on a board 2cm x 2cm.)

    Can anyone help me?
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    You didn't showing that how the pins connecting to as RED, BLK, YEL?
     
  3. tritechinc

    Thread Starter New Member

    Dec 21, 2015
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    Red is VCC (+12vdc), Blk is GND and YEL is the circuit output of which has +12vdc on it. When the circuit operates it should pull YEL to ground. I don't understand why the emitter is tied to VCC, then goes through that resistor to the transistor base. I want to know if this circuit would actually work, if not then I have something wrong. (But I don't think I do)
     
  4. ScottWang

    Moderator

    Aug 23, 2012
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    There is no the right opto transistor, so I can't analyze further, the circuit could be like as the right one.

    Photo-Transistor Circuit.gif
     
  5. hp1729

    Well-Known Member

    Nov 23, 2015
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    Wow! given those three parts the most likely configuration (figure G) is the farthest from your findings. :)
     
  6. tritechinc

    Thread Starter New Member

    Dec 21, 2015
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    hp1729 That is very helpful! Thank you!
     
  7. tritechinc

    Thread Starter New Member

    Dec 21, 2015
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    0
  8. hp1729

    Well-Known Member

    Nov 23, 2015
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    Have you considered just putting a voltage on it and see what it does? +5 V to red, ground to back. Tie a pullup resistor from yellow to +V. Shine a light on the sensor (IR TV remote?) and see if the output goes low.
     
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