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 transistor. An NPN Transistor can be formed by sandwiching p-type material or acceptor atoms between two n-type materials in a semiconductor substrate. Similarly, an PNP Transistor forms due to inserting n-type material or donor atoms between two p-type materials in same semiconductor substrate.
Earlier we have 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 region 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 positively, negatively and positively doping of emitter, base and collector region respectively.
Symbol of NPN Transistor
Symbol of PNP Transistor
The symbol of NPN and PNP Transistor 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 follow table.
|SL No.||NPN Transistor||PNP Transistor|
|1||To form a NPN Transistor we need to sandwich p-type doping between two n-type doping region.||To form a PNP Transistor we need to sandwich a n-type region between two p-type doping region.|
|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 carriers are free electrons||Majority 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 the above Differences:
- 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 type 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 carriers in NPN transistor are free electrons. On the other hand, Emitter and Collector region have p-type doping in PNP transistor. Therefore, majority carriers in PNP transistor are Holes. Then minority carriers in NPN transistor are Holes and in PNP transistor are free electrons.
- Free electrons have greater mobility than holes. Therefore NPN transistor responses faster than PNP transistor.
- NPN transistors have huge applications than PNP transistors. This is because of faster responses of NPN transistor.
Thus, in this article we learned how to differentiate between NPN and PNP Transistor. There are some other posts in this website related to Transistors. One can 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.