NPN Bipolar Junction Transistor BJT component

The NPN Bipolar Junction Transistor (BJT) uses a controlled amount of current flowing through it’s base to emitter to allow a multiple amount of current (gain) to flow from collector to emitter and other components that are part of that circuit.

Check the datasheet for the part number and package (component appearance) for pin layout and specific properties of the exact transistor you are using.

  • 2N2222 – Original and best known BJT.
  • 2N3904 – Common NPN BJT that has a PNP counterpart, the 2N3906.

I use these transistors a lot in my YouTube videos at

NPN Bipolar Junction Transistor BJT terminals.

  • Collector – N type material attached to a terminal that is connected to the positive side of the circuit
  • Base – P type material sandwiched between Collector and Emitter, attached to a terminal that connects to the control signal that ultimately determines how much current can pass through .
  • Emitter – N type material attached to a terminal that connects to the more negative side of the circuit.


When you pass a certain amount of current/electron flow through the base to emitter of a bipolar junction transistor, a multiple amount of current (known as the transistor’s current gain) will be permitted to pass from collector to emitter. The exact gain of a transistor varies between part number and even then there are manufacturing differences and operating conditions that affect a particular transistors gain. Transistor circuits are designed to not rely on a transistor’s gain.

Any donations will help me update this site faster and make more YouTube videos!

As an Amazon Associate I earn from qualifying purchases
  • This website is only intended to provide supplemental information to those already studying electronics. It takes no responsibility for how that information is used and the possible injuries or other damage that may arise