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

    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

    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.
    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.

  2. ISB123

    Well-Known Member

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


    Feb 5, 2014
    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
    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
    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
    Unfortunately, the datasheet had no arrows. Maybe the gap on the emitter was a image-processing error that should have been an arrow.

  7. cmartinez

    AAC Fanatic!

    Jan 17, 2007
    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


    Aug 23, 2012
    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.