Difference Between NPN and PNP Transistor

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Difference NPN and PNP Transistor

PNP is a Bipolar Junction Transistor or BJT in which holes are the major current carriers, while electrons are minor. The arrangement of the PNP transistor is in such a way that the P-type doped semiconductor is separated by a thin layer of N-type doped semiconductor material.


NPN is another BJT in which electrons are the major current carriers, while holes are minor. The arrangement of NPN transistor is in such a way that two N-type doped semiconductors are separated by a thin layer of P-type doped semiconductor material embedded between them.


Differentiate Between NPN and PNP Transistor

Do you know what is the difference between NPN and PNP transistor?

The basic difference between an NPN transistor and PNP transistor is indicated by the arrow of the current flow. If the current points outwards, it is NPN, and if the current points inward, it is an NPN transistor.

To understand in detail, let’s distinguish between NPN and PNP transistor in tabular form:


Distinguish Between NPN and PNP Transistor

NPN Transistor

PNP Transistor 

The full form of NPN transistor is a Negative Positive Negative Transistor.

The full form of PNP transistor is a Positive Negative Positive Transistor.

NPN transistor can be better understood in the following way:


N - Never

P - Points 

N - In


It means the current points in the outward direction.


NPN transistors are used as a sink to the current i.e., current flows to the Collector.

In PNP, we can differentiate it from NPN in the following way:


P - Points

N - In

P - Permanently


It means the current points inwards.


PNP transistors are used as a source to the current i.e., current flows out of the Collector.

In the NPN transistor, electrons are important current carriers.

In the PNP transistor, holes are major/important current carriers.

NPN transistors behave like two NP junction diodes when connected back to back with the cathode diodes.

PNP transistor behaves like two PN junction diodes when connected back to back.


PNP transistor remains OFF for positive voltage and ON when small output current and a negative voltage is at its base w.r.t the emitter.

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The direction of the current is from Collector to Emitter, as, indicated by the arrow in the figure.

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The direction of the current is from Emitter to Collector, as, indicated by the arrow in the figure.

At ON state, PNP sensors produce a positive output.

On state, NPN sensors produce a negative signal or output.

When the transistor is turned on, the electrons enter its base. 

When the transistor is turned on, holes enter its base.

Inside current: Since electrons are mobile and are at varying positions because of which inside current develops in the NPN transistor. 

Inside current: Inside current in PNP transistor develops because of the varying positions of holes.

Outside current: An outside current develops because of the flow of holes in the transistor. 

Outside current: an outside current develops because of the flow of electrons in the transistor. 

High conduction occurs because of the high flow of electrons.

Comparatively low conduction because of fewer electrons. 

Switching time is faster in NPN transistors.

A switching time is slow in PNP transistors.

The path of the positive voltage is along with the Collector terminal. 

The path of the positive voltage is along with the Emitter terminal.

Forward biased: Emitter base junction is forward biased.

Forward biased: Emitter base junction is forward biased.

Reverse biased: Collector Base junction is reverse biased.

Reverse biased: Collector Base Junction is reverse biased.

Small current: Small current flows from Emitter to Base Junction 

Small current: A small current flows from Base to Emitter Junction.

Ground Signals are low in NPN transistors.

Ground signals are high in PNP transistors.


PNP and NPN Transistors

PNP and NPN transistors are opposite in their functionality. When you apply current to the Base Junction of the NPN transistor, it allows more power to flow through it; that’s why NPN are considered good for amplifiers. However, the PNP does the opposite. When you apply current to the Base junction of the PNP transistor, it shuts off.

Both transistors function as a valve. If you turn it one way and the water (electricity) is able to flow, and if you turn it the other way, it does not. Both of the transistors make up the fundamental components of Logic Gates for processing digital signals in computers and other electronic devices.

The other places we use transistors are sensors, amplifiers, oscillators, detectors, modulators, and various electric circuits to perform functions.


Summary

So, we understood that both PNP and NPN transistors are current controlling devices where conduction is carried out by charge carriers viz: holes and electrons. When major carriers are electrons, it is an NPN transistor, and when there is a majority of carriers that are holes, it is a PNP transistor.

FAQ (Frequently Asked Questions)

Question 1: Write Two Applications of Transistors?

Answer: The applications of transistors lie hereunder:

  • Transistor as an Amplifier: Transistors have the ability to control large amounts of current that’s why they are used to boost the power of audio, radio and television signals.

  • Transistor as a Switch: Transistors have the ability to switch on and off the signals at high speeds because of this they form the basis of modern electronic devices that run billions of operations per second.

Question 2: What is a Transistor? Write its Working Principle.

Answer: Transistor is a semiconductor device that is the basis of many modern electronic devices. It works on the principle/idea that the emitter terminal of the transistor is connected to the negative terminal of the battery.


When the circuit completes, the Emitter-Base junction becomes forward biased, and the Base-Collector becomes reverse biased. In this situation, no current flows through the device.

Question 3: Can we Use PNP Instead of NPN Transistor?

Answer: Yes!

PNP transistors can be replaced by NPN transistors. All we need to do is we need to make a difference in polarities of voltage and the flow of current.

Question 4: Which Better NPN or PNP?

Answer: NPN is better than PNP because NPN carries a plethora of mobile charges viz: electrons for the conduction of electricity.