BJT(bipolar junction transistor)

BJT(bipolar Junction transistor)

• Junction transistor is a solid state device,generally it is called as Bipolar Junction Transistor (BJT). 
• The BJT transistors  are formed between three layers(three terminals), these are called emitter (E), Base (B), Collector (C). 

  

  transistor

•  The BJT transistors are current-controlled devices. If small amount of current flows through the base of a BJT transistor then it causes to flow large current from emitter to collector. The BJT transistors are only the transistors which are turned ON by the input current which is given to the base. 
• 1. Base(B) layer :-
                               It is a very thin layer, the thickness is about 25 microns it is a central              region of the transistor.
  
  2. Emitter(E) layer:-
                               The emitter region is heavily doped, since emitter has to supply majority carriers.
  
  3. Collector(C) layer:-
  
                               The collector region is lightly doped. since it has to accept majority charge carriers, it is large in size hence emitter and collector can not be interchanged.
  
• The BJT transistors are classified into PNP and NPN transistors.