Bipolar Junction Transistors

What is a transistor?

A three terminal active semiconductor device that transforms current flow from a low resistance path to a high resistance path.

How many types of charge carriers are involved in transistor conduction?

Two types: Electrons and Holes.

What are the two junctions in a bipolar junction transistor (BJT)?

Emitter Base Junction and Collector Base Junction.

Why is it called a Bipolar Junction Transistor?

Because it involves both types of charge carriers (electrons and holes) and has two junctions.

What is the role of the emitter in a transistor?

It supplies charge carriers to other regions and is heavily doped.

What distinguishes the base region of a transistor?

It is the middle region that forms two PN junctions and is lightly doped.

What is the function of the collector in a BJT?

It collects the charge carriers, is larger than the emitter and base, and has intermediate doping levels.

What are the two types of BJT?

PNP Transistor and NPN Transistor.

How is a PNP transistor structured?

It consists of two P regions supported by an N region.

What structure characterizes an NPN transistor?

It consists of two N regions separated by a P region.

What does the arrow in the BJT circuit symbol indicate?

The direction of the conventional current flow between the base terminal and the emitter terminal.

How are the base-emitter and base-collector junctions described?

The base-emitter junction is where the emitter connects to the base, and the base-collector junction is where the collector connects to the base.

What biasing condition is necessary for proper transistor operation?

The EB junction must be forward biased and the CB junction must be reverse biased.

What happens during forward bias in an NPN transistor?

Electrons in the N type emitter flow towards the base, constituting the emitter current Ie.

What is the equation representing the relationship between emitter, collector, and base current in an NPN transistor?

Ie = Ib + Ic.

How much of the emitter current typically recombines with holes in the base region?

About 5%.

What happens to the majority of the electrons in the base of an NPN transistor?

95% enter the Collector region, constituting the Collector current IC.