Operating Regions of Transistor
There are two junctions in a transistor: emitter-base and collector-base junction. These junctions could be forward-biased or reverse biased. Based on the biasing of the transistor of emitter-base and collector-base junction there are four regions of transistor:
⦁ Active region
⦁ Saturation region
⦁ Cut-off region
⦁ Inverted region
Active region
This is a region of operation where emitter-base junction is forward-biased and collector-base junction is reverse-biased.
Voltage VEB is connected between emitter and base in a forward-biased manner and voltage VCB is connected between collector and base in a reverse-biased manner. When a transistor is in active region then it is mainly used for amplification. In this region, collector current depends upon base current.
Saturation region
This is a region of operation where emitter-base junction is forward-biased and collector-base junction is also forward-biased.
Voltage VEB is connected between emitter and base in a forward-biased manner and voltage VCB is connected between collector and base in a forward-biased manner. In this region, collector current becomes independent of the base current. When a transistor is in saturation region then it acts like a closed switch.
Cut-off region
This is a region of operation where emitter-base junction is reverse-biased and collector-base junction is reverse-biased.
Voltage VEB is connected between emitter and base in a reverse-biased manner and voltage VCB is connected between collector and base in a reverse-biased manner. In this region the value of current in the transistor is nearly zero. It is so because emitter does not emit ay charge carrier to base except few minority charge carriers which are generated thermally. When a transistor is in saturation region then it acts like an open switch.
Inverted region
This is a region of operation where emitter-base junction is reverse-biased and collector-base junction is forward-biased.
Voltage VEB is connected between emitter and base in a reverse-biased manner and voltage VCB is connected between collector and base in a forward-biased manner. In this region transistor is does not work properly. This region is not of much importance.
Region of operation |
Emitter-base junction |
Collector-base junction |
---|---|---|
Active region |
Forward-biased |
Reverse-biased |
Saturation region |
Forward-biased |
Forward-biased |
Cut-off region |
Reverse-biased |
Reverse-biased |
Inverted region |
Reverse-biased |
Forward-biased |
BJT Configurations
A transistor is also called as bipolar junction transistor or simply BJT. It is called as bipolar as only two types of charge carriers, i.e. majority charge carriers and minority charge carriers are required to perform the operations on transistor. BJT is a current-controlled device as the output voltage, current or power is controlled by the input current in the transistor. As we know, BJT is a three-terminal device , so the three configurations- we will study in this article. The three main configurations are – common emitter , common base and common collector , which has its unique characteristics and applications respectively.
Table of Content
- What is BJT?
- Configurations
- Operating regions of transistor
- Advantages
- Disadvantages
- Applications
- Comparison between CB, CE and CC configurations