How to Identify NPN and PNP Transistor using Multimeter

How to Identify NPN and PNP Transistor (BJT) using Multimeter?




Imagine from your component box, you have picked couple of Bipolar Junction Transistors (BJTs) and you don't know whether they are NPN or PNP  type transistors... (Almost everyone would have face this problem)

In this post, we will discuss about how to find out the NPN and PNP transistor using multimeter...

Before proceeding further, let us refresh about how to identify the transistor terminals.

Identifying BJT Terminals:

We know that the Bipolar junction transistor has three terminals namely 

  1. Emitter (E)
  2. Base (B)
  3. Collector(C)

The transistors are available with various packages in the market. Let us discuss about the TO-92 package.

Keep the transistor such that the flat surface facing towards you as shown in the below figure:
BJT_Terminal_no_identificationNow starting from left, mark like 1,2 and 3. They are respectively 

  1. Emitter (E)
  2. Base (B)
  3. Collector(C)

The schematic symbol of the BJT is given below:

BJT_Schematic_Symbol

Identifying BJT Types:

Both NPN and PNP transistor looks similar in physical appearance. We can not differentiate by seeing them. We need a multimeter to identify the type of BJT.

Remember the following points:

  1. The transistor internally has  two diodes (NPN ≡ N - P - N ≡ NP Junction + PN Junction and PNP ≡ P - N - P ≡ PN Junction + NP Junction).
    ie,Emitter to  base is one PN junction ( diode) and Base to collector another PN junction (diode).
  2. In the diode mode, the multimeter will show the voltage when we keep the positive probe of the multimeter to the anode of the diode and negative probe  to the cathode.
  3. If the multimeter positive probe is connected to the cathode of the diode and the negative probe to the anode, then it will not give any voltage (showing zero).




Steps to identify the NPN type transistor:

  1. Keep the Multimeter in the Diode mode.
  2. Keep the positive probe to the center pin (Base) of the transistor. 
  3. Touch the negative probe to the pin-1 (Emitter). You will see some voltage in the multimeter.
  4. Similarly touch the negative probe to the pin-3 (collector) with respect to the pin-2. You will see some voltage in the multimeter.
  5. It will ensure that it is a NPN transistor. The logic behind this is, in NPN transistor
    Emitter (E) - N type material - Equivalent to cathode of the diode
    Base (B) - P type material - Equivalent to anode of the diode
    Collector(C) - N type material - Equivalent to cathode of the diode
  6. If the multimeter positive probe is connected to anode and negative probe is connected to cathode, then it will show voltage. If the connections are interchanged it will not show any value.

Steps to identify the PNP type transistor:

  1. Keep the Multimeter in the Diode mode.
  2. Keep the positive probe to the pin-1 (Emitter) of the transistor. 
  3. Touch the negative probe to the center pin (Base). You will see some voltage in the multimeter.
  4. Similarly touch the negative probe to the center pin (Base) with respect to the pin-3 (collector). You will see some voltage in the multimeter.
  5. It will ensure that it is a PNP transistor. The logic behind this is, in PNP transistor 
    Emitter (E) - P type material - Equivalent to anode of the diode
    Base (B) - N type material - Equivalent to cathode of the diode
    Collector(C) - P type material - Equivalent to anode of the diode
  6. If the multimeter positive probe is connected to anode and negative probe is connected to cathode, then it will show voltage. If the connections are interchanged it will not show any value.



With the help of above mentioned steps we can identify NPN and PNP transistor using multimeter. How can we ensure that the transistors are in good condition and failed?. Please read the post How to test transistor using Multimeter?

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Please leave your comments below...

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41 Responses

  1. Marcville says:

    Thanks for that helpful information

  2. Moroski says:

    Thank you very much!!

  3. Sean Smith says:

    Doesn't this article ignore the difference between TO-92A, TO-92B and TO-92C?

  4. MD.MAHBUB HASAN says:

    Tt was my great problem.Thank you.

  5. Felisi Buddy says:

    Thank you so much..this is great..

  6. shuvrajeet das says:

    very well

  7. Akeel says:

    Thanks, but how to identify pins EBC

    • Olivia says:

      You'll have to note the Model No. and look up the data sheet in order to find that out.

    • Ahmed says:

      collector is less oum than emitter when tested by AVO ..
      It mean collector is nearest to zero oum than emitter ..
      use AVO: And hold the first lead to the "base" the other lead move it to collector time and emitter another time .. the collector should read less oum than the emitter ..

  8. nasiru sani says:

    thanks that's helpful information

  9. Shehzad Wasim says:

    Thanks for giving very useful informations.

  10. obio says:

    so helpful thanks@
    obio

  11. Jayesh unakar says:

    Thanks for informing and if possible crystal how to check by multimeter informarion ptovide so we learn

  12. Ben Bitok says:

    Thank you got the point.

  13. Eze Chukwuma says:

    I found this article useful. Many thanks to the author.

  14. rey says:

    Thanks a lot...

  15. Emmanuel E. says:

    I appreciate. This explanation is very usefull

  16. sanjeet says:

    Thanks for provided good information

  17. JACKSHON says:

    THANK YOU FOR EVERYTHING

  18. Schadrack says:

    Thank you. Now i get what i want.

  19. Ranga Reddy says:

    Very useful information is explained very clearly. Thank you!

  20. Richard says:

    Great! Thanks so much.

  21. talent says:

    thanks a lot ..nice eplanation

  22. deepu says:

    thank you

  23. Jaydeb says:

    Thank you very much

  24. Andrew nyagawa says:

    Thanks

  25. KAWEESI FRED says:

    Thnks

  26. Evansmobela says:

    Nice explanationa

  27. Qudratullah says:

    Very nice sir you do solve my large problem
    I am very thsnksfull to you

  28. Aman bharti says:

    This Information about transistor is very good . But I have a question
    As you show the pin diagram identification in fig for EBC. But some have CBE as respect series. This is confusion about pin out. Identification

  29. Lekayo Mugezi says:

    The information is very useful thanks

  30. amanchopade says:

    if suppose in condition where i dont have the npn transister and i have pnp transister but i need npn transister in the circuit then can i use the npn transister

  31. Kaushal says:

    It helped me a lot. Thanks

  32. Nitin Patel says:

    Thanks for teaching /providing in simple & perfect manner. Really very useful ....

  33. Arun says:

    How to identify collector or emitter

  34. RICHARD says:

    THANKS, YOU HAVE MADE IT VERY SIMPLE TO UNDERSTAND

  35. Honesty says:

    Thanks for this wonderful info. It helpful

  36. Ivyson says:

    Thanks, this is going to help me a lot in my upcoming exams

  37. Tetuai says:

    So wonderful its so helpful for me and rest

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