嵌入式 - 双极性晶体管和场效应晶体管的简单介绍

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最新推荐文章于 2025-11-02 23:57:33 发布 · 895 阅读

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#笔记

How Transistors Work (BJT and MOSFET) - The Simple Explanation

March 7, 2024March 17, 2021 by Øyvind Nydal Dahl

The transistor is a simple component that you can use to build a lot of fun projects. In this hands-on guide, you’ll learn how transistors work so that you can use them in your next circuit.

And it’s actually pretty easy, once you learn the basics. I’ll focus on the two most common transistors here; the BJT and the MOSFET.

The transistor works like an electronic switch. It can turn a current ON and OFF. A simple way to think about it is to look at the transistor as a relay without any moving parts. A transistor is similar to a relay in the sense that you can use it to turn something ON and OFF.

But a transistor can also be turned partly on, which is useful for building amplifiers.

How Transistors Work (BJT)

Let’s start with the classic NPN transistor. It’s a Bipolar Junction Transistor (BJT) and has three legs:

Base (b)
Collector (c)
Emitter (e)

If you turn it ON, current can flow through it from the collector to the emitter. When it’s OFF, no current can flow.

In the example circuit below, the transistor is OFF. That means no current can flow through it, so the Light-Emitting Diode (LED) is also off.

To turn the transistor ON, you need a voltage of about 0.7V between the base and the emitter.

Get Our Basic Electronic Components Guide

Learn how the basic electronic components work so that circuit diagrams will start making sense to you.

If you had a 0.7V battery, you could have connected it between the base and emitter, and the transistor would have turned ON.

Since most of us don’t have a 0.7V battery, how do we turn on the transistor?

Easy! The base-to-emitter part of a transistor works like a diode. A diode has a forward voltage that it “grabs” from the available voltage. If you add a resistor in series, the rest of the voltage drops across the resistor.

So you’ll automatically get around 0.7V by adding a resistor.

This is the same principle you use