Question

What is called a bipolar transistor?

Answer 1

A **bipolar transistor** is a type of transistor that uses both electron and hole charge carriers. It is a semiconductor device with three layers of semiconductor material, typically made of silicon, and has three regions: the **emitter**, the **base**, and the **collector**. These layers are doped differently to create two types of semiconductors: **n-type** and **p-type**.

There are two main types of bipolar transistors:

1. **NPN transistor**: The order of the layers is n-type (emitter), p-type (base), and n-type (collector).
2. **PNP transistor**: The order of the layers is p-type (emitter), n-type (base), and p-type (collector).

The name **"bipolar"** comes from the fact that both **electrons** (negative charge carriers) and **holes** (positive charge carriers) are involved in the conduction process. This is in contrast to a **unipolar** transistor like the **field-effect transistor (FET)**, where only one type of charge carrier is used (electrons or holes).

**Functioning of a Bipolar Transistor:**
- In an **NPN transistor**, when a small current flows from the base to the emitter (through the base-emitter junction), it allows a larger current to flow from the collector to the emitter (through the collector-emitter junction).
- In a **PNP transistor**, the process works in the opposite direction.

Bipolar transistors are widely used in **amplification** and **switching applications**. Their ability to amplify signals makes them essential components in electronics such as radios, amplifiers, and digital circuits.