Transistor is one of the basic circuit components for electronic devices. The main purpose of a Transistor is to Amplify electronic signals. There are two types of BJT Transistors – NPN and PNP. In another article, we discussed the construction, symbol and other properties of BJT Transistors. In this article, we’re going to discuss the differences between NPN and PNP Transistors based on those properties.
Differences between NPN and PNP Transistors
The 10 differences between NPN transistors and PNP transistors are listed in the following table.
|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.
|The doping of the emitter region is n-type.
|The doping of the emitter region is p-type.
|Base region is doped with p-type impurity.
|Base region is doped with n-type impurity.
|Doping of the collector region is n-type.
|Doping type of the collector region is p-type.
|The direction of current flow is outward from the Emitter terminal and Inward at Collector and Base terminals.
|The direction of current flow is inward at the Emitter terminal and outward in Collector and Base terminals.
|The majority of carriers are free electrons.
|The majority of carriers are holes.
|Minority carriers are holes.
|Minority carriers are free electrons.
|Operation time is relatively faster.
|Operation time is relatively slower.
|NPN transistors are used most frequently.
|PNP transistors are rarely used.
|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 an NPN transistor, Emitter and Collector regions are doped with n-type while the base region is doped with p-type. But the doping of 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, the Emitter-Base junction is Forward Biased and the Collector-Base terminal is reverse-biased to use as an amplifier. But the current flow in NPN transistor is inward at the Base and Collector terminals and outward at the Emitter terminal. In the case of PNP transistors, the current flow is inward at the Emitter terminal and outward at the Base and Collector terminals.
- As the two regions (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 transistors. Therefore, the majority carriers in PNP transistors are Holes. The minority carriers in NPN transistors are Holes and in PNP transistors 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.
In this article, we learned how to differentiate NPN and PNP Transistors. If you have any doubts on this topic you can ask me in the comment section.