Circuits – How to identify PNP and NPN Transistors (with a Simple Circuit)

In this project I’ll make one of the easiest PNP and NPN circuit identifier on earth. You’ll see how easy It is to make one! I’ve also made a post to help you learn more about the Transistors theory. (I highly recommend you to read it first).

This project is great to learn more about:

  • Transistors
  • Simple DIY Circuits
  • PNP and NPN TransistorsElectronics components, transistors

Parts Required:

  • 1x LED
  • 1x Pushbutton
  • 1x 1k Ohm Resistor
  • 1x 10k Ohm Resistor
  • 1x Breadboard
  • 1x 9V Battery (and Battery Clip)
  • Some Wires

Schematics

Pnp circuit schematics

Final Product

PNP and NPN transistor identifier

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PNP and NPN transistor identifier

Watch out it works:

Basically when you put a PNP transistor on the circuit the LED turns ON if you hit the pushbutton. If you put a NPN transistor on the Circuit the LED will stay OFF.

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8 thoughts on “Circuits – How to identify PNP and NPN Transistors (with a Simple Circuit)”

  1. But what about which leg of the transistor is which, which is the emitter, which is the base, and which is the collector, not all transistors are the same, and your schematic which is actually a breadboard layout has no indication where the base, collector and emitter should go. The pin out of the transistor can be got from a data-sheet but your layout needs the extra information. Otherwise it only works some of the time – if you are lucky.

    • This always worked for me, but you’re right. that’s because I know the layout and how to insert the transistors…

      This circuit it’s pretty limited though.
      I might re-do this project later.

      Thanks for your help David,
      Rui Santos

    • This simple circuit wasn’t designed with that in mind.
      But uou can create some sort of label on this small device… and when you insert the right transistor it says which pin is what.

  2. I got the breadboard version working but had difficulty figuring out the hard-wired version. Could you add some detail to that in the form of a schematic (vs. breadboard). Thanks!

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