Electronics, Transistor

Differences between NPN and PNP Transistor, NPN vs PNP

Before talking about Difference between NPN and PNP Transistor, we must first understand what is NPN transistor and PNP transistor.

Basically, NPN and PNP transistors are types of Bipolar Junctions Transistor (BJT), and BJT’s are the electronic component which is widely used for the amplification and switching purposes.

And in this article, we will learn about the differences between NPN and PNP transistor w.r.t their symbols, construction, operations.

Differences between NPN and PNP Transistors:

An NPN transistor or PNP transistor is made up of two types of semiconductors i.e. (P-type semiconductor and N-type semiconductor), an N-type semiconductor is consist of Electrons in the majority and P-type semiconductor is consist of Holes in the majority, the operation of these NPN or PNP transistor involves both Holes and Electrons.

  • In NPN transistor the majority carriers are Electrons and minority carriers are holes.
  • In PNP transistor the majority carriers are Holes and minority carriers are electrons.

 The main difference between NPN and PNP transistor is the use of proper biasing (Making transistor power ON).

An NPN transistor is powered ON when there is (+ve) high signal applied at the base terminal of NPN transistor. When the base of NPN is high the current starts to flow from collector terminal to Emitter terminal ( C to E).

A PNP transistor is turned ON when there is low signal applied to the base terminal of PNP transistor. When the base of PNP transistor is at the low state (GROUND) the current starts to flow from Emitter to Collector (E to C).

Summing up the concept, a PNP transistor turns ON with low state signal I.e. (0v Ground), and an NPN transistor turns ON with a high signal applied at the base (+volts).

This was the main difference between NPN and PNP transistor, in order to understand the physical and internal differences of both types of transistor we have to see their Symbols, Construction, and Operation.

 

Difference between NPN and PNP transistor w.r.t their Symbols:


Figure down below shows the difference between NPN and PNP w.r.t their symbols. Here you can see that an NPN and PNP transistor has three terminals knows as Emitter, Base, and Collector the only difference in symbols of both transistor is the direction of an arrow.

 NPN and PNP Symbol

Points to remember:


  • In case of NPN transistor, the Emitter terminal’s arrow is pointing outwards.
  • In case of PNP transistor, the emitter terminal’s arrow is pointing in.
  • NPN means Negative, Positive, Negative.
  • PNP means Positive, Negative, Positive.

 

Difference between NPN and PNP transistor w.r.t their Construction:


Construction of NPN transistor:

Construction of NPN transistor is shown below; here you can see Emitter and collector are formed from the N-type material whereas Base is formed from of P-type material.

NPN transistor Construction
NPN transistor Construction

The n-type material is also known as negative charges which are consisting of Electrons in the majority. And the P-type material is known as Positive charges which are consisting of Holes in the majority, also in NPN transistor Emitter and Collector are negatively charged whereas Base is positively charged.

Thus, a small positive charge at the base terminal can control the operation of amplification by allowing current to flow from Emitter to collector terminal.

Usually, NPN transistor is widely used because they are easy to manufacture they have electrons as a majority carrier hence NPN transistors have more electron mobility which means they can perform faster than PNP transistors, they are negatively grounded whereas PNP transistors are positively grounded making circuit difficult for connections. These are the few reasons, therefore; designers prefer NPN transistors over PNP transistors.

Construction of PNP transistor:

Construction of PNP transistor is shown below; here you can see Emitter and collector terminals are formed from the P-type materials whereas Base terminal is formed from the N-type material.

PNP transistor Construction
PNP transistor Construction

The p-type material is commonly known as Positive charges and in PNP Emitter-Collector is positively charge which means they have holes in the majority. Whereas N-type material is known as negatively charged and in PNP base is formed from the N-type material hence base have electrons in the majority.

Thus, a small amount a negative charge (GND) at the base terminal can control the operation of amplification by allowing current to flow from collector to Base terminal.

difference between NPN and PNP transisor construction

 

The main difference between NPN and PNP transistor is the use of correct biasing, the direction of current and voltage polarities are opposite for each transistor whereas the operation is quite same for both transistor, they both NPN and PNP are capable of performing the operation of amplification and switching.

 

Difference between NPN and PNP transistor w.r.t their Operation:


Both NPN and PNP are types of BJTs they are capable of performing similar tasks but the only difference between these both is the use of biasing and in this section, we will see how to make LED ON and OFF using the NPN and PNP transistor. This exercise will clear all the concepts of differences between NPN and PNP transistor.

 

Operation of NPN transistor:


An NPN transistor based circuit is shown below; the circuit is consisting of NPN transistor, Bias DC Supply, Switch, resistors, and LED.

Operation of NPN transistor
Operation of NPN transistor

Above circuit shows that the LED receives a positive voltages through DC supply the current is passing from LED to collector terminal but the circuit is not completed yet, so LED will not glow until we close the switch, when the switch is closed, base terminal will receive a positive supply therefore; base will allow the flow of current from collector to emitter hence circuit will be completed and LED will start to glow.

 

Operation of PNP transistor:


Operation of PNP transistor is quite difficult compared to NPN; down below you can see circuit is consist of PNP transistor, Bias DC supply, Switch, resistors, and LED.

Operation of PNP transistor

As in PNP transistor, Collector and Emitter are positively charged and Base is negatively charged. And we know base controls the current flow from Emitter to the collector, so in order to glow the LED, we have to make the base of PNP terminal at the low state and one thing we can do to achieve this is by making base terminal ground. The given figure above shows a LED circuit based on PNP transistor.

 The reason behind this is:

A PNP transistor gets positive voltages at emitter terminal. The positive voltages from emitter terminal will flow toward collector terminal when the base is supplied with low signal or GND.

When the switch will be closed base will receive low voltage (-ve) hence a low signal at base controls the current to flow from emitter to collector hence circuit path is complete, LED will starts to glow.

Comparison Chart

Difference between NPN and PNP transistor

PARAMETERNPNPNP
Definition An NPN transistor is consist of two layers of N-type semiconductor sandwiched on P-type Base.A PNP transistor is consist of two layers of P-type semiconductor sandwiched on N-type Base.
Type of Majority CarrierNPN has Electrons in MajorityPNP has Holes in Majority
SymbolNPN transistorPNP transistor
Flow of Majority CarrierElectrons flow from Collector to EmitterHoles flow from Emitter to Collector
Meaning of SymbolsNPN means Negative, Positive, NegativePNP means Positive, Negative, Positive
Direction of arrow in symbolIn NPN, arrow points outside.In PNP, arrow points inside.
Electrons MobilityIn NPN electrons mobility is faster because NPN is consist of Electrons.In PNP electrons mobility is less because PNP is consist of Holes.
Commonly UsedNPN is commonly used because it has more electrons mobilityPNP is less used due to less electrons mobility.
ConstructionNPN constructionPNP construction
Biasing NPN need high signal (+ve) at base terminal to perform operations.PNP need low signal (GND) at base terminal to perform operations.
Frequency ResponseNPN has fast frequency response than PNP due to fast electron mobilityPNP has slower frequency response than NPN transistor.

Key differences between NPN and PNP transistors


BJT or Bipolar Junction Transistor is three terminal devices (Emitter, Base, and Collector). There is a couple of PN junction diode in every BJT; back to back combination of diode forms the BJT transistor. The BJT transistor has two types NPN and PNP, Both are capable of performing amplification and switching operations most commonly we use NPN transistor because NPN transistors have faster electrons mobility and they are easy for designing circuits.

  • NPN and PNP transistor is the exact opposite of each in terms of their construction and flow of current.
  • In NPN transistor current flows from Collector to Emitter (C to E) whereas in PNP transistor current flows from Emitter to Collector (E to C).
  • NPN transistor is made up of two similar layers of N-type material both are sandwiched on a P-type material.
  • PNP transistor is made up of two similar layers of P-type material and both are sandwiched on an N-type material.
  • In NPN, N- stands for negative charges means electrons in the majority. And in PNP, P- stands for Positive charges means holes in the majority.
  • In terms of their symbols, both NPN and PNP symbols are almost same the difference is that in NPN transistor arrow points outward and in PNP transistor arrows points inside.
  • In terms of their working, NPN is power ON when the positive charge is applied at the base then current starts to flow from Emitter to collector. And PNP is power ON when there is a low signal (GND) is applied at the base then current starts to flow from Collector to an emitter.
Also Read:

  1. Introduction to BJT (Bipolar Junction Transistor)
  2. Transistor Configurations, Common Emitter, Base, and Collector Circuits
  3. Transistor Biasing, Fixed base, Collector bias, Emitter Bias, Voltage Divider Bias
  4. Common Emitter Amplifier, BJT Transistor Common Emitter Amplifier
  5. Common Base Amplifier, BJT Transistor Common-Base Amplifier
  6. Common Collector Amplifier, BJT Transistor Common-Collector Amplifier

This all about the difference between NPN and PNP transistor, in this article we learned NPN and PNP transistors differences w.r.t their symbols, constructions, operations. Furthermore, if you feel any query regarding this article feel free to write it below in the comment section or you have any suggestion comment down below, and Thanks for reading our article 🙂

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