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A transistor is a semiconductor that exchanges or transfers a weak signal from a sink resistance circuit to a source resistance circuit. Electrical signals such as current and voltage are regulated, methodized, and amplified by it.
These are unique in that they allow you to control the flow of current through the circuit. Transistors regulate and control the voltage between two leads to control the flow of current. There are three leads on each transistor.
NPN Transistor
A Bipolar Junction Transistor (BJT) is a form of NPN transistor. Electrons are the predominant current carriers, while holes are the lesser ones. Their arrangement is such that the layer of P-type doped semiconductors, which is a thin layer material implanted between them, separates the N-type doped semiconductors.
Emitter Current = Collector Current + Base Current
Working of NPN Transistor
- The majority of charge carriers in P-type semiconductors are electrons, which are repelled by the positive terminal of the battery VEE in emitter current IE .
- Since the electron density is lower, only 5% of holes reach the base with the electrons, causing the base current IB to appear. The base current is equal to 5% of IB .
- The remaining 95% is distributed among collectors. IC is the current of the collector, and it is 95 percent of IE .
- When the hole combines with the electrons in the base, it is compensated by electrons flowing from the battery’s negative terminal to the base through the wire.
- Because of the holes in this transistor, current flows. The flow of electrons creates current in the external circuit.
- From the circuit we get, IE=IB+IC.
PNP Transistor
A bipolar junction transistor is also known as a PNP transistor. In these, holes are the primary current-carrying source, while electrons play a minor role. Their arrangement is such that P-type doped semiconductor material is separated by a thin layer of N-type doped semiconductor material.
Emitter Current = Collector Current + Base Current
Working of PNP Transistor
- In N-type semiconductors, electrons make up the majority of charge carriers and are repelled by the negative terminal of the battery VEE in emitter current IE .
- The electron density is lower; only 5% of electrons enter the base with holes, causing the base current to IB appear. The base current is 5% of IB .
- The remaining 95% is distributed among collectors. The collector current IC is 95 percent of the IE .
- The passage of holes from a positive terminal of the battery to the base through the wire compensates the emitter when it mixes with the hole in the base.
- The current N-P-N transistor and external circuit are powered by electron flow.
- From the circuit we find, IC=IE–IB.
Difference between NPN And PNP Transistors
NPN Transistors | PNP Transistors |
One P-type thin layer separates two N-type layers. | A thin layer of N-type doped semiconductor material separates two P-type doped semiconductors. |
NPN- Negative Positive and Negative | PNP- Positive Negative and Positive |
When electrons enter the base, it turns on. | When holes are drilled through the base, it turns on. |
The current flows from the collector to the emitter. | Current flows from the Emitter to the Collector. |
Because of the different placements of electrons, it improves and unfolds. | It occurs as a result of electron flow. |
The switching time is quite quick. | It has a very slow switching time. |
Electrons make up the majority of charge carriers. | Holes make up the vast bulk of charge carriers. |
Holes make up a small percentage of charge carriers. | Electrons make up a small percentage of charge carriers. |
Collector Terminal | Emitter Terminal |
The current flows from the Emitter to the Base. | The current flows from the Base to the Emitter. |
Collector base junction | Collector base junction |
The ground signal is weak. | The ground signal is really strong. |
Important points about NPN and PNP Transistors
- A transistor is a semiconductor device that controls, organises, and amplifies electrical signals such as current and voltage.
- Electrons are the predominant current carriers in NPN transistors, while holes are the minor ones.
- In a PNP transistor, holes carry the majority of the current, while electrons play a minor role.
- The N-type emitter is connected to the negative pole and the P-type emitter is connected to the positive pole of the same battery VEE in forward biassing, and the P-type base is connected to the negative pole and the N-type emitter is connected to the positive pole of the same battery VCC in reverse biassing.
Conclusion
When an external potential is applied to its terminals, a transistor is defined as a three-terminal device built of semiconductor material that can operate as a conductor or an insulator (depending on the connection formed). In a bipolar diode, two separate types of charge carriers are responsible for conduction in transistors, therefore the name. This denotes the resistance being transferred from one area of the circuit to another. Switching and amplification are two essential features that it possesses due to its ability to modify its state.
Thus, transistors can be characterised as electronic devices that can be utilised as switches when a tiny amount of current is used to drive a greater current, such as to power a light-emitting diode, or when a small AC signal is amplified.
