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.
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.