11 May 2018

BJT modes of operation

The Bipolar junction transistor (BJT) is a junction transistor. It can be operated in three modes. The operation of the transistor in these modes is listed below :
  • Cute of mode
  • Saturation mode
  • Active mode
1. Cut of mode :
  • In cut of mode both of emitter to base and collector to base are reversed biased. 
  • In reverse bias condition, there is no current flow through the device, so there is no current flowing in the transistor.
  • So in this mode transistor is OFF state.
  • In off state mode of a transistor can be used switching operation for switch off application.
2. Saturation mode :
  • In saturation mode, both of collector to base and emitter to base is forward bias. 
  • In forward bias condition, current flow through the device, so electric current flow through the transistor.
  • So in this mode, free electrons flow from both of device emitter to base and collector to base.
  • In this mode huge current flow to the base of a transistor so at this stage transistor in going to saturation mode and that will be on ON state and acts as a closed switch.
So finally we conclude that above two modes of operation transistor as an ON/OFF switch.

3. Active mode :

  • In Active mode one junction Collector to a base reverse mode and other junction emitters to base forward bias.
  • So in this type of mode, it can be used as amplification of current.
Conclusion: So we can conclude that the transistor work as an ON/OFF switch when it is in saturation and cut off modes whereas it works as an amplifier of current in active mode.