Meaning of BJT

Bipolar Junction Transistor :
  • A BJT called a bipolar junction transistor is a three layer, two junction NPN or PNP semiconductor device with one p-region sandwiched by two n-region, Its called NPN transistor. With two p-region sandwiched one n-region, its called PNP transistor. First of all, let you know about BJT full form.
  • BJT are fabricated onto silicon integrated circuit chip. A single integrated circuit can contain many bipolar transistors, along with components such as capacitors, resistors,      and also diodes. 
  • The terms bipolar denotes that the current flow in the device is due to movement both side holes and electrons. 
  • A BJT has three terminal named collector (C), the emitter (E), and base (B). An emitter is indicated by an arrowhead indicating the direction of emitter current.
  • No arrow is associated with base or collector. The power transistor of NPN type is easy to manufacture and are cheaper also. 
  • Therefore, the use of power NPN transistor is very wide in high voltage and high current application. Hereafter, NPN  transistor would only be considered. 
  • Both NPN and PNP transistor are same in some way and related with each other but they may have differed from each other too. 
Why BJT used :

BJT used in many electronics circuits because base-emitter voltage varies as the logarithm of the base-emitter and collector-emitter currents. 
BJT can also be used to compute logarithms and anti-logarithms.  
Various diodes can also perform these nonlinear functions but the BJT provides more circuit flexibility.