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 the PNP transistor, the majority of charge carriers are holes, wherein 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 an 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 the PNP transistor, the flow of current runs from the emitter terminal to the collector terminal. As a result, a PNP transistor switches ON by a low signal, where an NPN transistor switches ON by a high signal.

Difference between NPN and PNP Transistor

The main difference between NPN and PNP transistors includes what are PNP and NPN transistors, construction, working, and their 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 of charge carriers are holes. Mainly, this transistor works the same as the NPN 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

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.

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 transistors 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 is 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.

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 onto the circuit. In the PNP transistor, the current runs through the collector to the emitter terminal.

Usually, an 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 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

The construction of the NPN transistor is shown below. The voltage at the transistor’s base is +Ve and –Ve at the transistor’s 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

This resistor restricts the current flow through the highest base current. In an 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 the 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.

Transistor Symbols

The schematic symbols of NPN and PNP transistors have extremely similar. The main difference is the path of the arrow over the emitter terminal. In an NPN transistor, the arrow symbol points outward, whereas, in a PNP transistor, the arrow symbol points inward.

The PNP transistor symbol is shown in the above figures where the arrow mark shows that the flow of current will be from emitter terminal to collector whereas, in an NPN transistor, the flow of current will be from collector to emitter terminal.

Which is better NPN or PNP?

Both the transistors like NPN and PNP are the BJTs. These are current controlling devices, especially used for amplifying & switching purposes. Generally, the NPN transistor is mainly used in the circuit as in NPN transistor the current conduction is due to the electrons whereas, in the PNP, the current conduction is due to the holes. When the electrons are more movable then the conduction of the NPN transistor is high.

The term NPN and PNP will show the voltage needs by the three terminals of the junction transistor-like base, emitter & collector. These two transistors are designed with different materials because the current development in them also changes. In some cases, once the voltage is given across the emitter then electrons will flow across the base & finally reach the collector terminal. This occurs due to the base terminal of these transistors is extremely thin as well as doped lightly.

NPN transistor more preferred as compared to PNP because we know that in PNP, holes are the majority charge carriers whereas, in NPN, electrons are the majority charge carriers. So, the holes’ mobility is not sped as compared to the electrons mobility. In different applications, different types of transistors are used like PNP & NPN. So, the mobility of holes is not fast as compared to electrons thus NPN transistor is more preferred.

Difference between NPN and PNP Transistor

One of the main differences between these two transistors is that in the NPN transistor, the flow of current will be in between the collector to emitter terminal once the positive supply is provided to the base terminal of the transistor. In the PNP transistor, the charge carrier supplies from the emitter terminal to the collector once a negative supply is provided to the base terminal. The difference between NPN and PNP transistor in tabular form are differentiated based on different factors.

The difference between NPN and PNP transistor includes the following.

Key Difference Between NPN and PNP Transistor

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

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 flowing 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 sandwiched of N-type. The NPN transistor is made up of two N-type material layers with a layer 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 the PNP transistor, a +ve voltage is set to the emitter terminal to generate a flow of current from the emitter terminal to the 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 the 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 the 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.

Characteristics of PNP and NPN Transistor

The o/p characteristics of PNP and NPN transistors are similar. The main dissimilarity is that the PNP transistor characteristic curve turns 180 degrees to gauge the voltages of reverse polarity as well as the values of current. On the characteristic curve, the dynamic load line will exist to measure the value of the Q point. Similar to NPN, the PNP transistor is also used in amplifying as well as switching circuits.

How to Identify PNP and NPN Transistor

There are different steps involved in identifying PNP and NPN transistors.

For NPN Transistor

• In the multimeter, select the mode of meter to the diode.
• Place the positive probe of the meter to the base terminal of the transistor
• Place the negative probe to the emitter terminal of the pin so that voltage can be noticed within the meter
• In the same way, place the negative probe at the collector terminal with respect to pin 2, then you can observe the voltage within the multimeter.
• So, this is known as NPN transistor
• The emitter terminal is an n-type material, that is equal to the cathode terminal of the diode
• The base terminal is a p-type material that is equal to an anode terminal of the diode
• The collector terminal is an n-type material that is equal to a cathode terminal of the diode.
• If the positive and negative probe of the multimeter is connected to anode & cathode terminals, then it will display voltage. If these connections are exchanged it will not display any value.

For PNP Transistor

• In the multimeter, select the mode of meter to the diode.
• Place the positive probe at the emitter terminal of the transistor.
• Place the negative probe at the base terminal, then you can notice some voltage within the multimeter.
• In the same way, place the negative probe toward the base with respect to the collector terminal then you can observe some voltage within the multimeter.
• So it will make sure that it is a PNP transistor and the main logic behind this mainly includes the following.
• The emitter terminal is a P-type material that is equal to the anode terminal of the diode
• The base terminal is an N-type material that is equal to a cathode terminal of the diode
• The collector terminal is a P-type material that is equal to an anode terminal of the diode

If the positive probe of this multimeter can be connected toward the anode terminal whereas the negative probe can be connected toward the cathode terminal, after that it will display some voltage. If both the connections are exchanged then it will not display any value.

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?