Transistor is one of the basic circuit components for electronic operations. The main purpose of a Transistor is to Amplify electronic signals at the output of a circuit. We already know that there are two types of Transistors – NPN and PNP. An NPN Transistor can be formed by sandwiching p-type material or acceptor atoms between two n-type materials in a semiconductor substrate. Similarly, a PNP Transistor forms due to inserting n-type material or donor atoms between two p-type materials in the same semiconductor substrate.
Earlier we discussed the construction, symbol and other properties of NPN and PNP Transistor. In this article, we are going to discuss the difference between NPN and PNP Transistor based on those properties. So, this article is basically on NPN vs PNP transistor.
Full form of NPN Transistor
The full form of NPN Transistor is Negative Positive and Negative Transistor. It is called NPN because it contains the doping of Emitter, base and collector regions with negative, positive and negative majority charges respectively.
What is the full form of PNP Transistor
Again, the full form of PNP Transistor is Positive Negative and Positive Transistor. This is because of the doping of emitter, base and collector regions with positive, negative and positive charges respectively.
Symbol of NPN Transistor
Symbol of PNP Transistor
The symbol of NPN and PNP Transistors are shown in fig.1 and fig.2 respectively.
Difference between NPN and PNP Transistor in tabular form
The differences between NPN transistor and PNP transistor are listed in the following table.
|SL No.||NPN Transistor||PNP Transistor|
|1||To form an NPN Transistor we need to sandwich p-type doping between two n-type doping regions.||To form a PNP Transistor we need to sandwich an n-type region between two p-type doping regions.|
|2||Doping of emitter region is n-type.||Doping of emitter region is p-type.|
|3||Base region is doped with p-type.||Base region is doped with n-type.|
|4||Doping of collector region is n-type.||Doping type of collector region is p-type.|
|5||Direction of current flow is outward from Emitter terminal and Inward at Collector and Base terminal.||Direction of current flow is inward at Emitter terminal and outward in Collector and Base terminal.|
|6||Majority of carriers are free electrons.||Majority of carriers are holes.|
|7||Minority carriers are holes.||Minority carriers are free electrons.|
|8||Operation time is relatively faster.||Operation time is relatively slower.|
|9||NPN transistors are used most frequently.||PNP transistors are rarely used.|
|10||NPN transistor appears to be a current source in Common Emitter mode.||PNP transistor appears to be a current sink in common Emitter mode.|
Discussions of NPN vs PNP
- In NPN transistor Emitter and Collector region are doped with n-type while the base region is doped with p-type. But doping in PNP transistor is just opposite to that of NPN. Here Emitter and collector regions have p-type doping and Base region has n-type doping.
- In both types of transistors Emitter-Base junction is Forward Biased and Collector-Base terminal is reverse biased to use as an amplifier. But the current flow in NPN transistor is inward at Base and Collector terminals and outward at Emitter terminal. Current flow is inward at Emitter terminal and outward at Base and Collector terminal of PNP transistor.
- As the two region (Emitter and Collector) have n-type doping, the majority of carriers in NPN transistor are free electrons. On the other hand, Emitter and Collector regions have p-type doping in PNP transistor. Therefore, the majority of carriers in PNP transistor are Holes. The minority carriers in NPN transistor are Holes and in PNP transistor are free electrons.
- Free electrons have greater mobility than holes. Therefore an NPN transistor responds faster than a PNP transistor.
- NPN transistors have huge applications than PNP transistors. This is because of the faster responses of NPN transistors.
Thus, in this article, we learned how to differentiate between NPN and PNP Transistors. There are some other posts on this website related to Transistors. Do visit those articles from the menu bar at the top of the page or from the related post section. If you have any doubt on this topic you can ask me in the comment section.