Circuits – PNP and NPN Transistors

I’ve decided to write this post to support a bit of the theory behind my new project that identifies the PNP and NPN transistors easily. (you should see my project after reading this post)

The difference between a PNP transistor and a NPN transistor is their polarity and their actions are reversed…

PNP TransistorPNP

  • A PNP transistor conducts from collector to emitter.
  • When you increase voltage to the base of a PNP transistor, the transistor is turned off more and more until it no longer conducts and completely shuts off.
  • And as you decrease voltage to the base of a PNP transistor, the transistor turns on more and more, until the transistor fully conducts from collector to emitter.

NPN Transistor

NPN

  • A NPN transistor conducts from emitter to collector.
  • When you increase voltage to the base of a NPN transistor, the transistor is turned on more and more until it conducts fully from emitter to collector.
  • And as you decrease voltage to the base of a NPN transistor, the transistor turns on less and less, until the voltage is so low, the transistor no longer conducts across emitter to collector, and shuts off.

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3 thoughts on “Circuits – PNP and NPN Transistors”

  1. This is a fantastic summary of the differences between PNP and NPN transistors. Thanks for writing up a side by side comparison that is quick and easy to get the basics.

    I find that I use NPN transistors far more often, but on occasion PNP’s are awfully useful. It’s great to keep this info handy as a refresher on occasion so that you can get back to designing, armed with the right info.

    Thanks for putting this together.

    Mike

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