How to Use Transistors

There are many tutorials out there on transistors. Hundreds. Thousands? However, I find most of them only teach you what's going on at the atomic level inside of the unit, and not so much how you should be using them in practice. Yeah, maybe the other guys have an example of a transistor (usually a NPN BJT or N-Channel MOSFET) actually doing something. However, if I gave you a task that needed to be fulfilled with a transistor, how would you practically go about choosing the right device? That practical understanding of the component isn't always so clear.

So I thought I would go ahead and put together an in-depth lesson on the practical knowledge you need to know to effectively use a transistor in your design. The transistor is such an important device and likely your projects will use them. You should know how to spec a suitable device. This starts with reading the datasheet of the device and understanding the functional limitations of the transistor. In this tutorial you will be able to answer the following questions:

  • How do these transistors work?
  • When should I use a NPN or PNP device? Or a N-Channel or P-Channel device?
  • Will this transistor work with the voltages I am working with?
  • What resistors should I use on the gate or base?
  • Why am I choosing these resistor values?
  • What heat dissipation solutions do I need, if any?

You don’t need anything to complete this tutorial.

  • The practical difference between NPN or PNP (or N-Channel and P-Channel) transistors
  • How to read a datasheet for a transistor, enabling you to spec out a transistor for your project
  • How to build a circuit around a transistor
  • How to calculate resistor values needed for your transistor circuit
  • How to calculate expected heat generation of the transistor during use
You may want to download a few things to get the most out of this tutorial: