Junction transistors

Junction transistor

There are two types of junction transistors: 

(1). P-n-p transistor

In it 'n' type crystal sandwitched between  2 'p' type crystals. 

Symbol of p-n-p transistor

(2). n-p-n transistor

In it,  'p' type crystal sandwitched between 2 'n'  type crystals

Symbol of n-p-n transistor

Elements of transistor

There are three elements of transistor:

(1). Emitter(E) 

It is highly doped semiconductor. It provides majority charge carriers . It is always forward biased with respect to any other part of transistor. 

(2). Base(B) 

It is middle section of the transistor. It is lightly doped it controls flow of majority charge carriers collector. 

(3). Collector (C) 

It is a heavily doped semiconductor having bigger size then emitter (E). It  collects the majority charge carriers emit from the emitter. It is always reverse biased with respect to any other part of transistor. 

             Action of n-p-n transistor

                                     Or

           Working of n-p-n transistor

I(E) = I(B)+ I(C) 

Where,       I(E) = emitter current

                     I(B) = base current

                     I(C) = collector current

(1). As emitter - base become forward biased the majority charge carriers in emitter starts to flow Through the base. 

(2). About 5% of majority charge carriers diffused in base and 95%  crossed the base. 

(3). The majority charge carriers reaches in collector and diffused at 'C'. 

(4). A small base current flows through the base - emitter and collector it means, current also flows from n-p-n transistor due to diffusion or recombination. 

Now, according to Kirchhoff's law

I(E) = I(B) + I(C) 

But IB is very small such that

I(E) = I(C) 

                                Note

The same type of working process we will see with p-n-p transistor in which we will get same equation

       

                   I(E) = I(B) + I(C) 

Though, as like n-p-n transistor, base current I(B) is also very small for p-n-p  transistor. 

So, 

            I(E) = I(C)