Difference Between NPN and PNP Transistor

The transistors PNP and NPN are BJTs and it is a basic electrical component, used in various electrical and electronic circuits to build the projects. The operation of the PNP and NPN transistors mainly utilizes holes and electrons. These transistors can be used as amplifiers, switches and oscillators. In PNP transistor, the majority charge carriers are holes, where in NPN the majority charge carriers are electrons. Except, FETs have only one sort of charge carrier. The major difference between NPN and PNP transistor is, an NPN transistor gets the power when the flow of current runs through the base terminal of the transistor.

In NPN transistor, the flow of current runs from the collector terminal to the emitter terminal. A PNP transistor switches ON, when there is no flow of current at the base terminal of the transistor. In PNP transistor, the flow of current runs from the emitter terminal to the collector terminal. As a result, a PNP transistor switch ON by a low signal, where NPN transistor switches ON by a high signal.

Difference between PNP and NPN
Difference between PNP and NPN

Difference between NPN and PNP Transistor

The main difference between NPN and PNP transistors includes what are PNP and NPN transistors, construction, working and its applications.

What is a PNP Transistor?

The term ‘PNP’ stands for positive, negative, positive and also known as sourcing. The PNP transistor is a BJT; in this transistor the letter ‘P’ specifies the polarity of the voltage necessary for the emitter terminal. The second letter ‘N’ specifies the polarity of the base terminal. In this kind of transistor, the majority charge carriers are holes. Mainly, this transistor works as the same as the NPN transistor.

PNP Transistor
PNP Transistor

The required materials used to build the emitter (E), base (B) and collector(C) terminals in this transistor are diverse from those used in the NPN transistor. The BC terminals of this transistor are constantly reversed biased, then the –Ve voltage should be used for the collector terminal. Consequently, the base-terminal of the PNP transistor must be –Ve with respect to the emitter- terminal, and the collector terminal must be –Ve than the base terminal

PNP Transistor Construction

The PNP transistor construction is shown below. The main characteristics of both the transistors are similar except that the biasing of the current & voltage directions are inverted for any one of the achievable 3-configurations namely common base, common emitter and common collector.

PNP Transistor Construction
PNP Transistor Construction

The voltage between the VBE (base and emitter terminal) is –Ve at the base terminal & +Ve at the emitter terminal. Since for this transistor, the base terminal constantly biased -Ve with respect to the emitter terminal. Also, the VBE is positive with respect to the collector VCE.

The voltage sources connected to this transistor is shown in the above figure. The emitter terminal is connected to the ‘Vcc’ with the load resistor ‘ RL’. This resistor stops the current flow through the device, which is allied to the collector terminal.

The base voltage ‘VB’ is connected to the ‘RB’ base resistor, which is biased negative with respect to the emitter terminal. To root the base current to flow through a PNP transistor, the base terminal of the transistor should be more negative than the base terminal by approximately 0.7volts (or) a Si device.

The primary difference between PNP and  NPN transistor is the correct biasing of the transistor joints. The directions of current and the voltage polarities are constantly reverse to each other.

What is an NPN Transistor?

The term ‘NPN’ stands for negative, positive, negative and also known as sinking. The NPN transistor is a BJT, in this transistor, the initial letter ‘N’ specifies a negatively charged coating of the material. Where, ‘P’ specifies a completely charged layer. The two transistors have a positive layer, which are situated in the middle of two negative layers. Generally, NPN transistor is used in various electrical circuits for switching and strengthens the signals that exceed through them.

NPN Transistor
NPN Transistor

The NPN transistor includes three terminals like base, emitter and collector. These three terminals can be used to connect the transistor to the circuit board. When the current flows through this transistor, the base terminal of the transistor gets the electrical signal. The collector terminal creates a stronger electric current, and the emitter terminal exceeds this stronger current on to the circuit. In PNP transistor, the current runs through the collector to the emitter terminal.

Usually, NPN transistor is used because it is so simple to generate. For an NPN transistor to function properly, it requires to be created from a semiconductor object, which holds some current. But not the max amount as extremely conductive materials such as metal. Silicon is one of the most normally used in semiconductors. These transistors are the simple transistors to build out of silicon.

The NPN transistor is used on a computer circuit board to translate the information into binary code, and this procedure is proficient through a plethora of tiny switches flipping On & OFF on the boards. A powerful electric signal twists the switch on, while a lack of a signal makes the switch off.

Construction of NPN Transistor

The construction of this transistor is shown below. The voltage at the transistor’s base is +Ve and –Ve at the transistors emitter terminal. The base terminal of the transistor is positive at all times with respect to the emitter, and also collector voltage supply is +Ve with respect to the transistor’s emitter terminal. In this transistor, the collector terminal is linked to the VCC through the RL

NPN Transistor Construction
NPN Transistor Construction

This resistor restricts the current flow through the highest base current. In NPN transistor, the electrons flow through the base represents transistor action. The main characteristic of this transistor action is the connection between the i/p and o/p circuits. Because, the amplifying properties of transistor come from the resultant control that the base utilizes upon the collector to emitter current.

The NPN transistor is a current activated device. When the transistor is turned ON, the huge current IC supplies between the collector & emitter terminals in the transistor. But, this only occurs when a tiny biasing current ‘Ib’ flows through the transistor’s base terminal. It is a bipolar transistor; the current is the relation of two currents (Ic/Ib), named the DC current gain of the device.

It is specified with “hfe” or these days beta. The beta value can be huge up to 200 for typical transistors. When the NPN transistor is used in an active region, then base current ‘Ib’ offers the i/p and collector current ‘IC’ gives the o/p. The current gain of the NPN transistor from the C to the Eis called alpha (Ic/Ie), and it is a purpose of the transistor itself. As the Ie (emitter current) is the sum of a tiny base current and huge collector current. The worth of the alpha is very close to unity, and for a typical low power signal transistor the value ranges from about 0.950- 0.999.

Main Difference Between PNP and NPN

PNP and NPN transistors are three terminal device, which are made up of doped materials, frequently used in switching and amplifying applications. There are a combined of PN junction diodes in every bipolar junction transistor. When the couple of diodes connected, then it shapes a sandwich. That seat a kind of semiconductor in the middle of the similar two types.

Difference between NPN and PNP Transistor
Difference between NPN and PNP Transistor

So, there are only two kinds of bipolar sandwich, that are namely PNP & NPN. In semiconductor devices, the NPN transistor has typically high electron mobility evaluated to the mobility of a hole. Thus, it allows a huge amount of current & works very fast. And also, the construction of this transistor is simple from silicon.

  • Both the transistors are collected of special materials and the flow of current in these transistors is also different.
  • In an NPN transistor, the flow current runs from the collector terminal to the Emitter terminal, whereas in a PNP, the flow of current runs from the emitter terminal to the collector terminal.
  • PNP transistor is made up of two P-type material layers with a layer of sandwiched of N-type. The NPN transistor is made up of two N-type material layers with a layer of sandwiched of P-type.
  • In an NPN-transistor, a +ve voltage is set to the collector terminal to generate a flow of current from the collector. For PNP transistor, a +ve voltage is set to the emitter terminal to generate flow of current from the emitter terminal to collector.
  • The main working principle of an NPN transistor is, when the current is increased to the base terminal, then the transistor switches ON & it performs fully from the collector terminal to emitter terminal.
  • When you reduce the current to the base, the transistor switches ON and the flow of current is so low. The transistor no longer works across the collector terminal to emitter terminal, and turns OFF.
  • The main working principle of a PNP transistor is, when the current exists at the base of the PNP transistor, and then the transistor turns OFF. When there is no flow of current at the base of the transistor, then the transistor switches ON.

This is all about the main difference between NPN and PNP transistors which are used to design electrical and electronic circuits and various applications. Furthermore, any doubts regarding this concept or to know more about different types of transistor configurations, you can give your advice by commenting in the comment section below. Here is a question for you, which transistor has higher electron mobility?

2 Comments

  1. HOW DOES IT WORKS…CAN YOU EXPLAIN IT… THIS IS SUDHEER FROM INDIA…

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