Top 5 Differences Between NPN And PNP Transistors

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The bipolar junction transistors exist as NPN and PNP types. This article intents to help you understand the difference between these two types and how to use them in a circuit. Also, this will be helpful to automation engineers and instrumentation engineers in understanding 3 wire sensor connections.

Transistors are made by combining two types of semiconductors: n-type and p-type. The n-type semiconductors carry electron donor atoms and p-type semiconductors carry electron acceptor atoms (holes).

NPN transistors: NPN stands for Negative Positive Negative. Contains two regions of n-type semiconductors with a p-type semiconductor in the middle.

PNP transistors: PNP stands for Positive Negative Positive. Contains two regions of p-type semiconductors with a n-type semiconductor in the middle.

PNP and NPN transistors do perform in a similar way when used in a circuit. But the polarity of voltage source connections and the direction of current flow differs. In most places, NPN transistors can be replaced with PNP and vice-versa but the polarity of the power supply needs to be changed.

NPN VS PNP TRANSISTOR
Figure shows structures of NPN and PNP transistors and their symbols

A bipolar junction transistor is a current controlled device. The output of the BJT can be controlled by controlling the base current.

Comparison of NPN and PNP transistors

NPNPNP
Terminal PolarityEmitter – NegativeBase – PositiveCollector – PositiveEmitter – PositiveBase – NegativeCollector – Negative
Load ConnectionLoad is connected between positive and the collector.Load is connected between emitter and ground.
Direction of conventional currentThe direction of conventional current flow is from the collected to the emitter.The direction of conventional current flow is from the emitter to collector.
Majority charge carriersElectrons are the majority carriers in NPN transistors.Holes are the majority carriers in NPN transistors.

Difference between NPN and PNP in terms of construction

Construction of NPN transistor
Construction of NPN transistor
Construction of PNP transistor
Construction of PNP transistor

NPN vs PNP: Difference in connection for sensors

The major difference between NPN and PNP lies in the way it is used in the circuit. From the sensor point of view, sensors with NPN output configuration acts as sinking output and those with PNP output configuration acts as sourcing output.

Source vs sink connection- NPN vs PNP

Read More: Digital I/O and Analog I/O , Bipolar Junction Transistors

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