What do you need to know about bipolar junction transistors?

What do you need to know about bipolar junction transistors?

Bipolar Junction Transistors (BJT) Transistor Basics. • A Bipolar Junction Transistor is a three layer (npn or pnp) semiconductor device. • There are two pn junctions in the transistor. • The three layers are called the emitter, base and collector.

How are alpha and beta related in a bipolar transistor?

Alpha and beta are related by the following identities: Beta is a convenient figure of merit to describe the performance of a bipolar transistor, but is not a fundamental physical property of the device.

What’s the difference between a BJT and NPN transistor?

BJTs exist as PNP and NPN types, based on the doping types of the three main terminal regions. An NPN transistor comprises two semiconductor junctions that share a thin p-doped region, and a PNP transistor comprises two semiconductor junctions that share a thin n-doped region.

When does a biasing current occur in a transistor?

However, this only happens when a small biasing current ( Ib ) is flowing into the base terminal of the transistor at the same time thus allowing the Base to act as a sort of current control input.

What is the name of the PN junction?

The pn junction joining the base region and the collector region is called the base-collector junction, as indicated in Figure 4.1(b). A wire lead connects to each of the three regions, as shown. These leads are labeled E, B, and C for emitter, base, and collector, respectively.

What is the beta of a NPN transistor?

The values of Beta vary from about 20 for high current power transistors to well over 1000 for high frequency low power type bipolar transistors. The value of Beta for most standard NPN transistors can be found in the manufactures datasheets but generally range between 50 – 200.

What happens to free electrons in a p-n junction?

As will be stated later, in forming a p-njunction some of the free electrons in the n-type crystal can drift away into the p-type material thus forming a local positive electric charge in a region in the n-type silicon crystal.