TRANSISTORS

TRANSISTORS

• A transistor is a semiconductor device that contains three regions separated by two distinct PN junctions. The two junctions are EB junction and CB junctions. 
• The central region is called base. 
• The two outer regions are called emitter and collector. 
• There are two types of charge carriers, electrons and holes hence transistor is called bipolar transistor. 
• Transistor can be viewed as two PN junction diodes arranged back-to-back with base being common to both the diodes. 
• As soon as the two junctions are formed, majority charge carriers diffuse and form two depletion layers. Depletion layer is narrow at EB junction and wide at CB junction.

There are two types of transistors: 

1.NPN transistor--P-type sandwiched between two N-type. 

2.PNP transistor--N-type sandwiched between two P-type.

FUNCTIONS OF THREE REGIONS IN TRANSISTOR: 

Emitter, Base and Collector are three regions in a transistor. 

Emitter:  

• It emits charge carriers. 
• It is heavily doped and has moderate size. 
• It is located at the one end of transistor. 

Base: 

• The base controls the flow of charge carriers from emitter to the collector. Therefore, it acts as a gate between emitter and collector. 
• It has minimum thickness and is lightly doped. 
• It makes the central region of a transistor. 

Collector: 

•  It collects the charge carriers coming from the base. 
• It has largest size with moderate doping. It is moderately doped. 
•  It is at the other end of a transistor.

Biasing of transistor 

• The Emitter-Base (EB) junction of transistor is always forward biased, and CollectorBase (CB) junction of transistor is always reverse biased. 
• Therefore, it works in an active mode. Hence, it transfers current from low resistance region (EB) to high resistance region (CB). 
• It is seen that almost same current flows through the two junctions. 
• Thus, the device is called as transistor- the shortened form of transfer resistor

CIRCUIT CONFIGURATION 
COMMON BASE CONFIGURATION

TRANSISTOR ACTION

APPLICATIONS OF TRANSISTOR 

• It is used in switching electronic circuits.
• It is used as an amplifier.
•  It is used in integrated circuits.