The configuration obtained by the NPN transistor is negative-positive-negative. In this type of transistor, the P-type semiconductor is placed between two N-type semiconductors. The transistor performs the function of switching and amplification.
NPN Bipolar Transistors
In NPN, the collector contains much positive charge as compared to both base and emitter. This is a three-terminal device with an emitter, base, and collector. Below given figure shows the circuit diagram of the NPN transistor:
The figure shows that VCC is connected to the collector by a resistor RL, which is used to protect the connected load. RB is connected to the VB to limit the base current:
NPN carries the negative current between the emitter and collector through the base region. This transfer of current links input and output and this is the main feature of the NPN transistor. A transistor is also known as a current-driven device, and it is fully ON by the IC current flow between the emitter to collector. The current gain between the emitter and collector is known as alpha (). The DC current gain is the ratio of IC and IB, and it is represented by Beta ().
The mathematical derivation for alpha and beta is given below:
Now by combining both alpha and beta:
The below figure shows the characteristic curve of the NPN transistor, in this figure, it is clearly shown that the Q-point moves between the saturation and cutoff region as the current IC decreases:
Transistor as switch
The figure shows that the transistor acts as a switch. We must place the collector and emitter of our transistor where the two switch connections are because we want to control the current flowing through the bulb. The emitter current must flow in the direction of the given arrowhead.
Example of NPN transistor
The below figure shows the NPN transistor, beta=50, and the value of VBE=0.8v find emitter base collector voltage. Firstly, find the emitter voltage:
These results show that the transistor is in active mode.
Conclusion
The transistor is a basic component used in the electronics circuit to amplify the signal or to switch on or off the circuit. P-type semiconductors are placed between two N-type semiconductors in an NPN transistor. The configuration obtained by the NPN transistor is negative-positive-negative.
