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Identify base, collector, and emitter of transistor

Discussion in 'General Electronics Discussion' started by pidja105, Jan 8, 2016.

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  1. pidja105

    pidja105

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    Oct 16, 2015
    Question is in the title, please answer.
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    You need to look up the datasheet. All the information is there.

    Martin
     
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  3. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    The information should be in the post, not the title, why do people do this, very enoying. Give us the name of the transistor.
    Adam
     
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  4. Bluejets

    Bluejets

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    hevans1944 and davenn like this.
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    We really do need our own tutorials. This is the second time this week that we had to post a link (OpAmp) to AC. It really sucks having to send new members there. :(

    On another note nubes are fortunate that they were born in a era that Germaniums are just history. The tests in that link would have produced a trash can full of seemingly bad transistors. o_O

    Chris
     
  6. Martaine2005

    Martaine2005

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    I have to take issue with this method, especially as it depends on the sensitivity of a meter.
    Just to clarify, I have four meters. Three digital and one analog. And never ONCE have I successfully been able to identify Emitter or Collector.
    There is obviously the possibility that I am just plain dumb! But it does seem to depend on the pressure applied to the probes and how sharp they are too.. (readings CAN differ minutely)..
    So I certainly wouldn't trust that method as a beginner...

    Martin
     
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  7. Martaine2005

    Martaine2005

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    Uncle Chris,
    John seems to like them!!:p

    Marty
     
  8. Arouse1973

    Arouse1973 Adam

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    As far as the transistor is concerned it does not matter if you reverse collector or emitter. So yes how you going to tell which is which unless you know the base terminal and swap the other two terminal and see which way draws more current.
    Adam
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    well... The reverse breakdown voltage of the base emitter junction I'd far lower than the base collector junction, so it will care if there is more than about 8v across it.

    A transistor will exhibit some gain with the emitter and collector reversed, but far less. This is probably the best way to distinguish them.

    For devices with a heat sink or metal case, if this is connected to anything, it week be the collector. In fact, TO-3 devices only have 2 leads. You connect to the body of the device as the collector connection.
     
  10. Arouse1973

    Arouse1973 Adam

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    Thanks Steve, I should have said as far as operation of the transistor is concerned.Not any limitations of the device.
    Adam
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yeah, I know what you meant. The transistor doesn't know it's connected the wrong way. It will just to transistor things with what it's given. :)

    I just wanted to make sure nobody misinterpreted your post as "it doesn't matter which way around you connect the collector and emitter".
     
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  12. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yeah, the fact that the probes incite the little bugger to do back flips and dance around your bench top doesn't help. Oxidation, oils, etc on the probes or transistor leads don't help when measuring the minute voltage differences indicated in the link. Alligator jumpers introduce their own issues.

    That said, we've all used a multimeter as shown at one time or another. For me, more times than I can remember. Once I've determined if it's an NPN or PNP using the base junction test I'm forced to use Alligator jumpers for my next test. Using the jumpers I connect the meter between the still unknown Collector - Emitter legs. If it was determined to be an NPN I wet my finger and bridge the + meter lead with the Base while watching the meter. I'm looking for current gain. If I don't see any significant reading I swap the unknown Collector -Emitter and try again.

    Chris
     
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  13. Martaine2005

    Martaine2005

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    Uncle Chris,
    That is so true. Doing back flips all over the table.
    I just look up the datasheet. I can happily work out whether it's NPN or PNP though.
    Your comment earlier about throwing out good transistors because of that test is also a good point.
    I had a situation last month where I threw away a bunch of LEDs, thinking they were dead. It never crossed my mind to reverse the polarity. So I had a whole bunch of LEDs with the larger internal section (cathode) actually being the anode. Needless to say, I rescued each and every one from the bin:D This image I found saved them.

    upload_2016-1-10_14-44-56.jpeg
    Marty
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I have a small device with three leads that takes most of the skill of of it. Connect the device and press a button...

    however with progress comes problems. It can identify ge and si devices but sometimes comes really unstuck on schottky diodes.
     
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  15. Martaine2005

    Martaine2005

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    I bought a cheap component tester that sounds similar. It gets confused between inductors and resistors. So not very useful. But it is pretty accurate with transistors so far. I just don't trust them and still check the datasheet to see if it's correct!
    Kind of counterintuitive..

    Martin
     
  16. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Think about what a fun uC project this would make. Imagine it cycling through the pinouts using safe current and voltage limiting. Then outputting the data to an LCD along with serial interface to a PC to create a log file.

    Chris
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    When I first began working at the hospital that I've mentioned before I was using a DMM that had the (+) (-) jacks reversed when in "R" & Diode Check mode! :eek: I Sharpy marked a warning on the rubber case.

    Chris
     
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  18. Arouse1973

    Arouse1973 Adam

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    I had this same thought Chris, a universal transistor tester. Each leg would have three LEDs located near to the leg, each one labelled BCE and then which ever light lights indicates that terminal is either base, collector or emitter. Martin, I just found your next project :)
    Adam
     
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  19. Martaine2005

    Martaine2005

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    Let me see what I can come up with:).
    Sounds like fun..
    Got to finish my roast dinner first....

    Martin
     
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  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Adam, the attached is a screen shot of a Picaxe project. The screen shot properties says I snapped it in 2012. At the time I was hot to trot to build a Picaxe based Transistor Curve Tracer. The screen shot is of an ISIS (Picaxe VSM) spice simulator drawing the curves generated by a Picaxe 08M and an NPN DUT. The idea was to build this and output the Picaxe data via RS232 to a PC and VB6 program that would draw the curves. This project never got finished.

    Ten years ago I did a complete remodel of my kitchen and living room. New floor, cabinets, counter top, sink, lighting ... the whole nine yards. All that was needed to finish it was put on the new molding. Yup, my wife is still waiting.

    Chris

    CurveTracer.JPG
     
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