is this a pnp or npn photo transistor (qre1113)

Discussion in 'General Electronics Chat' started by dolomite dave, Aug 29, 2015.

  1. dolomite dave

    Thread Starter New Member

    Aug 13, 2009
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    0
    Hi,

    i am looking to use a Fairchild QRE1113gr but i cant figure out what type of photo transistor it is. let me explain my confusion, the data sheet shows this

    [​IMG]
    pin 3 being the collector and pin 4 being the emitter. surly this makes this a pnp arrangement, but when i have searched google for this part every application i find shows this part as an npn type like this.
    [​IMG]
    so is it an npn or pnp type? what could i look for in the datasheet to help me know which one it is. i must admit i am more inclined to think it is a npn and due to the fact that people are using this device in this way.

    thanks
    Dave
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    It's optoisolator, transistor is npn.
     
    Last edited: Aug 29, 2015
    planeguy67 likes this.
  3. Denesius

    Member

    Feb 5, 2014
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    I agree, the Fairchild datasheet is confusing. But, the difference in the maximum rating between the Vceo (30V) and the Veco (5V), is a good way to tell which way the C-E junction is setup. It is the equivalent of a NPN
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It is a reflective proximity sensor, not an opto-isolator.

    @dolomite dave
    I have never seen a PNP phototransistor, I don't believe they exist and I see no point in making one, I couldn't imagine how it would work. Phototransistors are NPN.

    The pins are clearly labelled in the datasheet.

    These sensors work very well. We used them on a mini sumo bot last year.
     
  5. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Easy rule of thumb: When looking at any transistor's graphic, when it's NPN, it's arrow Never Points In... and when it's PNP, it's arrow Points iN Permanently.
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Unfortunately, the datasheet had no arrows. Maybe the gap on the emitter was a image-processing error that should have been an arrow.

    image.jpg
     
  7. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Right... interesting to see that the OP's original image doesn't show the gap, or the collector-emitter pin assignment
     
    GopherT likes this.
  8. ScottWang

    Moderator

    Aug 23, 2012
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    It's easy to identify that it is an npn phototransistor, the normal b of npn bjt is the current flows through from outside into b to e, but the b of pnp bjt is the current flows through from e to b to outside.

    The diagram shown that the phototransistor receive the reflection light from outside and converts the light energe to current flows through b to e, so that is an npn phototransistor, I can't imagine that how a pnp phototransistor going to works like that.
     
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