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Common emitter amplifier

Common Emitter Amplifier, BJT Transistor Common Emitter Amplifier

In this article, you will be able to learn and understand the Common Emitter Amplifier its Working, characteristics, and their applications.

In our previous discussions, we learned that a transistor can be configured in three different modes, the most widely used transistor configuration is Common-Emitter Configuration, and this is due to the reason, that a common emitter configuration provides good voltage and current gain.

What is the common emitter amplifier?

Common Emitter Amplifier has Emitter terminal as common for both input and output. Input is applied to the Base-Emitter terminal and output is taken from Emitter-Collector terminal.

 common emitter amplifier

The base-emitter junction is forward bias and emitter-collector junction is reverse bias, it is because a transistor must remain in an active region in order to perform amplification.

In order to understand the working of Common Emitter amplifier let’s first understand how does a transistor work as an amplifier?

How Transistor Amplifies?

When a weak AC signal is given to the base of the transistor, a small base current IB starts flowing. Due to transistor action, a much larger (β times the base current) a.c. current flows through the collector load RC. As the value of RC is quite high (usually 4-10 kΩ), therefore, a large voltage appears across RC.

Thus, an applied weak signal at the base circuit appears in amplified form in the output of collector terminal. It is in this way that a transistor acts as an amplifier.

Common Emitter Amplifier Working:

 As shown below a Common Emitter amplifier is made up of voltage divider bias, the input is Base-Emitter terminal and output is Emitter-Collector collector. During Positive cycle of input, a sinusoidal AC signal is applied at the input terminals of a circuit that cause the forward bias of base-emitter junction hence VBE is increased resulting in an increase in IB.

The collector current Ic is increased by β times with the increase in IB, hence VCE is correspondingly decreased.

common emitter amplifier working

common emitter amplifier working

Calculation:

formula of vo=vcc-icrc

Thus in a Common-Emitter amplifier, a positive going signal is converted into a negative going output signal i.e..180° phase shift is introduced between output and input signal and it is an amplified version of an input signal.

Practical Common Emitter Amplifier Circuit

In order to perform amplification with a common emitter amplifier, we must consider the basing, capacitor and different resistors values.

Figure down below shows the circuit of practical common emitter amplifier.

 

common emitter amplifier circuit

common emitter amplifier circuit

Here:

  • C1 and C2: These two capacitors are placed in the input and output of an amplifier; they are used to couple one circuit with another hence they are called as coupling capacitors.
  • CB: This capacitor is known as bypass capacitor which is used to bypass the AC signal to ground. It is very helpful because any noise signal that may be presented in AC signal will be passed out from bypass capacitor.
  • R1 and R2: These are places in between of collector to the base terminal they provide biasing to the transistor hence they are known as biasing resistors.
  • RC: RC is placed in the collector terminal in order produce faithful amplification. It places an important role in the operation of amplification (VC-VCC-ICRC)
  • RE: This RE resistor is placed in the emitter terminal of a transistor, and it is useful to control the gain of an amplifier.

Common Emitter Transistor Characteristics:

  • It has Large Voltage and Current Gain.
  • It has hence large power gain.
  • It has input to output phase shift of 180°.
  • It has moderate input and output impedance.

The voltage gain of Common Emitter Amplifier:

  • The voltage gain of Common Emitter amplifier is the ratio of output voltage to the input voltage.
  • Here output voltage is referred to as ΔVC and input voltage is referred to as ΔVB.
  • Av=β Vc/vb.

The current gain of Common Emitter Amplifier:

  • Current gain in CE amplifier is the ratio of output current to the input current. In CE configuration the current gain is denoted by greek symbol beta.
  • the output current is referred to as Ic and input current is referred to as Ib.
  • β=Ic/Ib

Input Impedance of CE Amplifier: 

The input impedance is also an important parameter in CE amplifier, because when a one CE amplifier drive another amplifier circuit then the output of one amplifier is input for another amplifier.

In CE amplifier input impedance is around 1kΩ-2k, input impedance values changes with respect to circuit configuration usually CE amplifier has input impended in between mentioned values.

Zin = R1 || R2 | | Zin (base)

Output Impedance of CE amplifier:

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The output impedance of the CE amplifier is the resistance looking in at the collector and is approximately equal to the collector resistor. The output impedance of CE amplifier is around 50k-70k.

Rout = RC

Input characteristics Of Common Emitter 

Input characteristics curve of a common-Emitter amplifier is the curve between IB and VBE whereas VCE is constant.

 input characteristcis curve of common emitter amplifier

Output characteristics of Common Emitter

Output characteristics curve of a common-Emitter amplifier is the curve between IC and VCE whereas IB is constant.

output characteristcis curve of common emitter amplifier

Applications of Common Emitter Amplifier:

why common emitter amplifier is widely used?

Common Emitter amplifier configuration is widely used due to its advantage of moderate current and voltage gain.

  • It is used in Audio Amplifiers
  • It is used in Microphones, RADIO, and Music Players
  • It is used in the Frequency generation circuit to increase the strength of the input signal.
  • It is used to increase the speed of Fans, Motors, and Timer circuits.

Advantages of Common Emitter Amplifier:

Common Emitter Amplifiers is most widely used amplifier than the Common Base amplifier and Common Collector amplifier because:

  1. An Ideal amplifier must have very low input impendence, and CE amplifier has very low input impendence.
  2. An Ideal amplifier must have very high output impendence, and CE amplifier has very high output impendence.
  3. It provides 180° phase shift. Or we can it is inverting amplifier.
  4. The current gain and voltage are moderate.

Disadvantages of Common Emitter Amplifier:

  • In the CE amplifier, there is high thermal instability.

Also, read:

  1. Common Base Amplifier, BJT Transistor Common Base Amplifier
  2. Common Collector Amplifier, BJT Transistor Common Collector Amplifier
  3. What is the Difference Between NPN and PNP Transistor
  4. Transistor configurations, Common Emitter, Common Base, Common Collector, and Applications
  5. Transistor Biasing, Self Bias, Emitter Bias, Voltage Divider Bias, and applications
  6. Introduction to BJT Transistor.

Conclusion:


In Common Emitter Amplifier, Input is applied to B-E Junction and Output is taken from E-C terminal, here emitter terminal is common for both input and output.

It is a widely used amplifier circuit because it provides good current gain and good voltage gain and it is also known as inverting amplifier because it gives 180° phase shift from input to output. It is widely used in audio amplification and signal amplification circuits.

Transistor Configurations ,Common Emitter, Base, and Collector Circuits

In this article, we are going to learn about Bipolar Junction Transistor Configurations, Common Emitter, Common Base and Common Collector. So far we have covered Introduction of Bipolar Junction Transistor.

We will learn in detail about different configurations of Bipolar Junction Transistor in this post, as we know that Bipolar Junction Transistor is a three terminal device, hence it can be configured in three different ways and we will cover these three different transistor configurations with respect to their circuit diagram, working, and advantages and disadvantages.

Introduction of Bipolar Junction Transistor Configuration:


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There are three terminals in BJT transistor named as Emitter, Base, and Collector. However, when we connect the transistor to any circuit we require four (4) terminals, two for input and two for output, to do that we make one terminal common to both input and output circuit.

The input is applied to that common terminal and one of the two terminal of BJT, and output is taken from the common terminal and remaining one terminal of BJT, Accordingly.

A Bipolar Junction transistor can be connected in a circuit in this three different ways.

  • Common Emitter Configuration –   It is the BJT configuration in which it behaves like an amplifier (it has both current and voltage gain).
  • Common Base Configuration –   It is the BJT configuration in which (it has Voltage Gain but no Current Gain).
  • Common Collector Configuration –   it is the BJT configuration in which it behaves like voltage buffer (It has Current Gain but no Voltage Gain).

These all (Bipolar junction Transistor configurations) have different advantages and disadvantage, and in this post, we will cover them one by one.

Common Emitter Configuration:


 

Common Emitter Configuration

Common Emitter Configuration

The term common-Emitter is derived from the fact that the emitter terminal is common to both the input and output sides of the configuration. This is the one famous configuration of BJT transistor, we mostly operate BJT transistor to this configuration because it allows us the operation of Amplification.

  • We apply input in the Base-Emitter terminal and we take an output from Emitter-Collector Terminal.
  • Here the input parameters are VBE, IB and output parameters are VCE, IE.

Current Amplification factor in Common-Emitter Configuration is represented by Beta (β).

The equation of β is:

β=IC/IB

This is a very important factor, the greater the beta β the greater the ability of transistor to amplify.

Few features of this configuration are:

  • It provides High input impedance and low output impedance.
  • It provides medium current gain and voltage gain.
  • It provides the 180* shift. (input and output is inverted at 180* phase).

Circuit diagram of Common Emitter configuration:

Circuit Diagram of Common Emitter Configuration

Circuit Diagram of Common Emitter Configuration

 

Input Characteristics Curve of Common Emitter Configuration:

It is the function of base current IB and VBE (base-emitter voltages) at constant collector-emitter voltage VCE.

  • Input characteristics curve can be obtained by keeping the output voltage VCE constant and varying the input voltage VBE and then record the value.
  • Now using these values we can draw a graph between the value of IB and VBE at VCE constant.

The equation for calculating the internal resistance at the input side is:

Ri= ΔVBE/ΔIB, (at VCE constant)

Input Characteristics curve of Common Emitter configuration

Input Characteristics curve of Common Emitter configuration

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Output Characteristics Curve of Common Emitter Configuration:

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It is the function of IC collector current and VCE collector-emitter voltage at making IB Base current constant.

  • Output characteristics curve can be obtained by keeping the input current IB constant and varying the output voltage VCE at different value and then record those values.
  • Now using those values we can draw a graph between the value of IC and VCE at IB constant.

The equation for calculating the internal resistance at the output side is:

Ro= ΔVCE/ΔIC, (at IB constant)

Output Characteristics Curve of Common Emitter Configuration

Output Characteristics Curve of Common Emitter Configuration

Also Read: Common Emitter Amplifier Working, Circuit and Advantages

Common Base Configuration:


The term Common-Base is derived from the fact that the base terminal is common to both the input and output sides of the configuration hence the name is given to this configuration is Common Base. One of the major uses of this configuration is to be used in cascade amplifiers, such as microphone pre-amplifiers or power amplifiers because of their high-frequency response.

  • We apply the input in the Base-Emitter terminal and we take an output from Base-Collector Terminal.
  • Here the input parameters are VBE, IE and the output parameters are VCB, IC.

The amplification factor in Common-base Configuration is represented by Alpha (α).

The equation of alpha α is:

α=IC/IE

Few important features of Common Base configuration are:

    • It provides High input impedance and low output impedance.
    • It provides low current gain and high voltage gain.
    • It provides the 0* phase shift. (input and output waveforms are identical in nature).

Circuit diagram of Common Base configuration:

Circuit diagram of Common Base configuration

Circuit diagram of Common Base configuration

Input Characteristics Curve of Common Base Configuration:

It is the function of input current IE and input voltage VBE (base-emitter voltages) at constant collector-base voltage VCB.

  • Input characteristics curve can be obtained by keeping the output voltage VBE constant and varying the input voltage VBE and then record the value.
  • Now using these values we can draw a graph between the value of IE and VBE at VCB constant.
Input Characteristics Curve of Common Base Configuration

Input Characteristics Curve of Common Base Configuration

The equation for calculating the internal resistance at the input side is:

Ri= Δ VBE/Δ IE, (at VCB constant)

Output Characteristics Curve of Common Base Configuration:

It is the function of the output current IC and out voltage VCB and making input current IE constant.

  • Output characteristics curve can be obtained by keeping the input current IE constant and varying the output voltage VCB at different value and then record those values.
  • Now using those values we can draw a graph between the value of IC and VCB at IE constant.
Output Characteristics Curve of Common Base Configuration

Output Characteristics Curve of Common Base Configuration

The equation for calculating the internal resistance at the output side is:

Ro= ΔVCB/Δ IC, (at IE constant)

Also Read: Common Base Amplifier circuit, Working, and Advantages.

Common Collector Configuration:


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Circuit Diagram of Common Collector Configuration

Circuit Diagram of Common Collector Configuration

The term Common-Collector is derived from the fact that the Collector terminal is common to both the input and output sides of the configuration hence the name is given to this configuration is Common Collector. One of the major uses of this configuration is to be used as a voltage follower or voltage buffer. This configuration allows you to handle large loads. And it is also widely used for impedance matching application because of their high input impedance property.

  • We apply input in the Base-Collector terminal and we take an output from Emitter-Collector Terminal.
  • Here the input parameters are VBC, IB and output parameters are VCE, IE.

The amplification factor in Common-base Configuration is represented by Gamma (γ).

The equation of gamma γ is:

γ= IE/IB.

Few important features of this configuration are:

  • It provides Very High input impedance and low output impedance.
  • It provides a high current gain and low voltage gain.
  • It provides the 0* phase shift. (input and output waveforms are identical in nature).

Input Characteristics Curve of Common Collector Configuration:

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It is the function of input current IB and input voltage VCB (collector-emitter voltages) at constant collector-emitter voltage VCE.

  • Input characteristics curve of the common collector can be obtained by keeping the output voltage VCE constant and varying the input voltage and input current VCB, IB and then record the value.
  • Now using these values we can draw a graph between the value of IB and VBC at VCE constant.
Input Characteristics Curve of Common Collector Configuration

Input Characteristics Curve of Common Collector Configuration

The equation for calculating the internal resistance at the input side is:

Ri= ΔVCB/ΔIB, (at VCE constant)

Output Characteristics Curve of Common Collector Configuration:

It is the function of the output current IC and out voltage VCE and making input current IB constant.

  • Output characteristics curve can be obtained by keeping the input current IB constant and varying the output voltage VCE at the different value and then record those values.
  • Now using those values we can draw a graph between the value of IE and VCE at IB constant.
Output Characteristics Curve of Common Collector Configuration

Output Characteristics Curve of Common Collector Configuration

The equation for calculating the internal resistance at the output side is:

Ro= Δ VCE/Δ IC, (at IB constant)

Also Read: Common Collector Amplifier circuit, Working and Advantages

Comparison between Common Emitter, Common Base and Common Collector configuration of a transistor:

comparison of different transistor configurations

comparison of different transistor configurations

Summary of Input and Output Parameters of Different Transistor Configurations: 

Summary of Input and Output Parameters of Different Transistor Configurations

Summary of Input and Output Parameters of Different Transistor Configurations

How to Determine the Transistor Configurations?


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one must be able to identify whether a given transistor is connected as a common emitter configuration, common collector or common base configuration. There is an easy way to identify it. Just find out the terminals where the input a.c. the signal is applied, and where the a.c output is taken from the transistor. The remaining third terminal is the common terminal.

For Example, if the a.c input is applied to the base terminal and the a.c output is taken from the collector terminal, then common terminal must be the emitter terminal. Hence the transistor is connected in common emitter configuration. Likewise, you can verify the rest of the configuration using this concept. Let’s say,

If the input is applied to the base terminal and output is taken from the emitter, then common terminal must be the collector terminal. Therefore, we can say the transistor is connected in the common collector configuration.

Conclusion:

Most Commonly Used Transistor Connection:

From all of three BJT transistor connections, the most commonly used transistor connection is a common emitter circuit, because it is the most efficient one. It is used in about 80-95 percent of all transistor applications.

The main reasons for the high use of this circuit arrangement are:

  1. High Current Gain
  2. High Voltage and Power Gain
  3. Moderate output to the input impedance ratio.

This is all about Transistor Configurations Common Emitter, Common Base, and Common Collector Configuration, we learned about working of different transistor configurations and their circuit diagrams. if you liked the article then comment below and share this information with your classmates and friends.

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Difference between diode and transistor

Difference Between Diode and Transistor, Diode Vs Transistor

Difference Between Diode and Transistor

Difference between Diode and Transistor is very important to understand because diode and transistor are considered as the heart of the electronic circuit.

The major difference between diode and transistor is that a diode is a current controlling device which allows the current in only one direction it has two terminals and it is mostly used for converting AC into pulsating DC.

On the other hand, A transistor is a three terminal device which allows the current form high resistance to low resistance region. The word transistor is composed of two words. 1: Transfer 2: Resistor.
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Thus, it is a device which transfers the resistance between input low resistance region to output high resistance region.

There are many differences between Diode and Transistor w.r.t their symbols, construction, operation, applications, and in this post, we will cover them one by one.

Difference Between Diode and Transistor Comparison Chart

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PARAMETERDIODETRANSISTOR
Definition Diode is a semiconductor device which allow current in only one direction.Transistor is a semiconductor device which transfers input signal of low resistance to output high resistance.
SymbolDiode symbol (2018)transistor symbol (2018)
TerminalsDiode is two terminal device (Anode (-), Cathode (+))Transistor is three terminal device (Base, Emitter, and Collector)
TypesDiode is classified in many types such as Zener Diode, Tunnel Diode, LED, Varactor Diode, Photodiode, Gunn Diode, Shcottkey Diode, .etc.Transistor is classified into two types: BJT Transistor and FET (Field Effect Transistor).
ConstructionDiode is formed when P-type material is joined with N-type material.Transistor is formed when Two same layer are joined together with alternative layers in between (N-P-N or P-N-P)
OperationDiode has two mode of operation. When Diode is forward bias it act as ON Switch and when diode is reverse biased it act as OFF SwitchTransistor has three mode of operations.
Active mode: (it act as Amplifier).
Saturation mode: (It act as ON Switch).
Cutt off mode: (It act as OFF Switch)
DeviceDiode is Uncontrolled device.Transistor is Controlled device. (output current can be controlled by varying voltages at base terminal).
Depletion RegionDiode has one depletion region (PN-region)Transistor has two depletion regions (PN and NP combined).
ApplicationsDiode is used in rectification, Clipping, Clamping, Voltage Multipliers, Power supplies, Protection Circuits .etc.Transistor is used for Switching and Amplification Purpose.

Definition


Diode

A Diode is a two terminal semiconductor device which is formed when a P-type semiconductor and an N-type semiconductor is combined together. The junction formed by joining these two semiconductors is known as PN junction and a simple PN junction is also called as Diode.

The diode is the most widely used electronic component which is almost used in every electronic circuit. It is used to provide AC conversion into Pulsating DC.

diode construction

Operation of a diode is simple when the PN junction is forward bias with the external bias battery the diode allows the flow of current and when the PN junction is reverse biased the diode does not allow the flow of current just like an open switch.

By connecting a Positive terminal of the battery with P-type material and a Negative terminal of the battery with N-type material PN junction can be made forward bias, this is the condition where a diode is mostly operated.

By connecting the Negative terminal of the battery with P-type material and Positive terminal with N-type material diode is made reverse bias.

Read More: What is the Duty Cycle?

What is Transistor


A Back-to-Back connection of two diode forms the transistor, a transistor is a three terminal device, and three terminals of a transistor are Emitter, Base, and Collector.

There are two junctions in the transistor Base-Emitter junction and Base-Collector junction. A transistor is capable of performing the operation of Switching and Amplification.

transistor construction

There are three operation modes of transistor commonly known as an Active region, Cut-off region, and Saturation region.

In Active region one junction is forward bias and one junction is reverse biased and transistor behaves as an amplifier, in the active region of transistor week signal is applied at the input and strong signal is achieved at the output.

In the saturation region, both junctions of a transistor are forward bias and the transistor behaves like a closed switch.

In Cut-off region, both junctions are reverse biased and transistor behaves as an open switch.

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Key Differences

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  1. One of the big difference between diode and transistor w.r.t their terminals is that diode has two terminal (anode and cathode) whereas the transistor has three terminals (Emitter, Base, and Collector).
  2. A diode is consist of one depletion region, whereas a transistor has two depletion regions
  3. In terms of their application diode is used for switching whereas a transistor is used for switching as well as amplification.
  4. In terms of their bias, the diode needs only one bias battery to operate whereas transistor utilizes two bias batteries for the operation.
  5. In terms of their working, the diode is the current controlling device it allows the current to flow in one direction whereas the transistor is a device which transfers the resistance between low resistance to high resistance region.
  6. The diode is formed from PN junction whereas a transistor is formed from two back to back connections of diodes.
  7. The diode is classified into different types such as Zener diode, Varactor Diode, Tunnel Diode, Light emitting diode, Photodiode, Gunn Diode, etc. whereas a transistor has only two types BJT (Bipolar junction transistor) and FET (Field Effect Transistor).
  8. In terms of their construction, a diode has two regions P-region and N-region, P-region is consist of holes in majority whereas N-region is consist of Electrons in a majority
  9. On the other hands, a transistor has three regions, Emitter region, Base region, and Collector region. The Base region have very less area, the collector region has a larger area whereas the emitter region has a moderate area.
  10.  The diode is utilized in Switching operations, Clipping circuit, clamper circuits, voltage multipliers, rectifiers, whereas a transistor is utilized for switching operations, amplification of audio signals, amplification of current or voltage signals.

Conclusion


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The diode is a two-terminal device which allows current to flow in one direction while the transistor is a three terminal device which passes current from input low resistance region to output high resistance region via the base.

A diode is used in various applications of electronics such as in rectification circuit, clipper, clamper, voltage multiplier, Power supplies, protection circuits, and switches etc.

A diode has two modes of operation and it is similar to a switch. it behaves as ON switch when it is forward bias, and it behaves as OFF Switch when it is reversed biased. Transistor can act as an Amplifier and a Switch, this application creates a major difference between Diode and transistor.

Diodes are classified into many different types such as Zener Diode, Tunnel Diode, Varactor diode, Photodiode, Light Emitting Diode, BARITT Diode, Gunn Diode, Schottky Diode, etc whereas Transistor is classified into two types Bipolar Junction Transistor and Field Effect Transistor.

It is considered that the diode is simple PN Junction whereas Transistor has two PN junction is formed by connecting back to back diodes.

Related Topics:

  1. Difference Between Clipper and Clamper Diode
  2. Difference Between NPN and PNP Transistor
difference between NPN and PNP transistor

Differences between NPN and PNP Transistor, NPN vs PNP

Before talking about Difference between NPN and PNP Transistor, we must first understand what is NPN transistor and PNP transistor? Basically, NPN and PNP transistors are types of Bipolar Junctions Transistor (BJT), and BJT’s are the electronic component which is widely used for the amplification and switching purposes and in this article, we will learn about the differences between NPN and PNP transistor w.r.t their symbols, construction, operations.

Comparison Chart

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Difference between NPN and PNP transistor

PARAMETERNPNPNP
Definition An NPN transistor is consist of two layers of N-type semiconductor sandwiched on P-type Base.A PNP transistor is consist of two layers of P-type semiconductor sandwiched on N-type Base.
Type of Majority CarrierNPN has Electrons in MajorityPNP has Holes in Majority
SymbolNPN transistorPNP transistor
Flow of Majority CarrierElectrons flow from Collector to EmitterHoles flow from Emitter to Collector
Meaning of SymbolsNPN means Negative, Positive, NegativePNP means Positive, Negative, Positive
Direction of arrow in symbolIn NPN, arrow points outside.In PNP, arrow points inside.
Electrons MobilityIn NPN electrons mobility is faster because NPN is consist of Electrons.In PNP electrons mobility is less because PNP is consist of Holes.
Commonly UsedNPN is commonly used because it has more electrons mobilityPNP is less used due to less electrons mobility.
ConstructionNPN constructionPNP construction
Biasing NPN need high signal (+ve) at base terminal to perform operations.PNP need low signal (GND) at base terminal to perform operations.
Frequency ResponseNPN has fast frequency response than PNP due to fast electron mobilityPNP has slower frequency response than NPN transistor.

Differences between NPN and PNP Transistors:

An NPN transistor or PNP transistor is made up of two types of semiconductors i.e. (P-type semiconductor and N-type semiconductor), an N-type semiconductor is consist of Electrons in the majority and P-type semiconductor is consist of Holes in the majority, the operation of these NPN or PNP transistor involves both Holes and Electrons.

  • In NPN transistor the majority carriers are Electrons and minority carriers are holes.
  • In PNP transistor the majority carriers are Holes and minority carriers are electrons.

 The main difference between NPN and PNP transistor is the use of proper transistor biasing (Making transistor power ON).

An NPN transistor is powered ON when there is (+ve) high signal applied at the base terminal of NPN transistor. When the base of NPN is high the current starts to flow from collector terminal to Emitter terminal ( C to E).

A PNP transistor is turned ON when there is low signal applied to the base terminal of PNP transistor. When the base of PNP transistor is at the low state (GROUND) the current starts to flow from Emitter to Collector (E to C).

Summing up the concept, a PNP transistor turns ON with low state signal I.e. (0v Ground), and an NPN transistor turns ON with a high signal applied at the base (+volts). This was the main difference between NPN and PNP transistor, in order to understand the physical and internal differences of both types of transistor we have to see their Symbols, Construction, and Operation.

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Difference between NPN and PNP transistor w.r.t their Symbols:

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Figure down below shows the difference between NPN and PNP w.r.t their symbols. Here you can see that an NPN and PNP transistor has three terminals knows as Emitter, Base, and Collector the only difference in symbols of both transistor is the direction of an arrow.

 NPN and PNP Symbol

Points to remember:

  • In case of NPN transistor, the Emitter terminal’s arrow is pointing outwards.
  • In case of PNP transistor, the emitter terminal’s arrow is pointing in.
  • NPN means Negative, Positive, Negative.
  • PNP means Positive, Negative, Positive.

Read More: What is the Duty Cycle?

Difference between NPN and PNP transistor w.r.t their Construction:

Construction of NPN transistor:

Construction of NPN transistor is shown below; here you can see Emitter and collector are formed from the N-type material whereas Base is formed from of P-type material.

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NPN transistor Construction

NPN transistor Construction

The n-type material is also known as negative charges which are consisting of Electrons in the majority. And the P-type material is known as Positive charges which are consisting of Holes in the majority, also in NPN transistor Emitter and Collector are negatively charged whereas Base is positively charged. Thus, a small positive charge at the base terminal can control the operation of amplification by allowing current to flow from Emitter to collector terminal.

Usually, NPN transistor is widely used because they are easy to manufacture they have electrons as a majority carrier hence NPN transistors have more electron mobility which means they can perform faster than PNP transistors, they are negatively grounded whereas PNP transistors are positively grounded making circuit difficult for connections. These are the few reasons, therefore; designers prefer NPN transistors over PNP transistors.

Construction of PNP transistor:

Construction of PNP transistor is shown below; here you can see Emitter and collector terminals are formed from the P-type materials whereas Base terminal is formed from the N-type material.

PNP transistor Construction

PNP transistor Construction

The p-type material is commonly known as Positive charges and in PNP Emitter-Collector is positively charge which means they have holes in the majority. Whereas N-type material is known as negatively charged and in PNP base is formed from the N-type material hence base have electrons in the majority. Thus, a small amount a negative charge (GND) at the base terminal can control the operation of amplification by allowing current to flow from collector to Base terminal.

difference between NPN and PNP transisor construction

The main difference between NPN and PNP transistor is the use of correct biasing, the direction of current and voltage polarities are opposite for each transistor whereas the operation is quite same for both transistor, they both NPN and PNP are capable of performing the operation of amplification and switching.

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Difference between NPN and PNP transistor w.r.t their Operation:

Both NPN and PNP are types of BJTs they are capable of performing similar tasks but the only difference between these both is the use of biasing and in this section, we will see how to make LED ON and OFF using the NPN and PNP transistor. This exercise will clear all the concepts of differences between NPN and PNP transistor.

Operation of NPN transistor:

An NPN transistor based circuit is shown below; the circuit is consisting of NPN transistor, Bias DC Supply, Switch, resistors, and LED.

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Operation of NPN transistor

Operation of NPN transistor

Above circuit shows that the LED receives a positive voltages through DC supply the current is passing from LED to collector terminal but the circuit is not completed yet, so LED will not glow until we close the switch, when the switch is closed, base terminal will receive a positive supply therefore; base will allow the flow of current from collector to emitter hence circuit will be completed and LED will start to glow.

Operation of PNP transistor:

Operation of PNP transistor is quite difficult compared to NPN; down below you can see circuit is consist of PNP transistor, Bias DC supply, Switch, resistors, and LED.

Operation of PNP transistor

As in PNP transistor, Collector and Emitter are positively charged and Base is negatively charged. And we know base controls the current flow from Emitter to the collector, so in order to glow the LED, we have to make the base of PNP terminal at the low state and one thing we can do to achieve this is by making base terminal ground. The given figure above shows a LED circuit based on the PNP transistor.

 The reason behind this is:

A PNP transistor gets positive voltages at emitter terminal. The positive voltages from emitter terminal will flow toward collector terminal when the base is supplied with low signal or GND. When the switch will be closed base will receive low voltage (-ve) hence a low signal at base controls the current to flow from emitter to collector hence circuit path is complete, LED will starts to glow.

Key differences between NPN and PNP transistors

BJT or Bipolar Junction Transistor is three terminal devices (Emitter, Base, and Collector). There is a couple of PN junction diode in every BJT; back to back combination of diode forms the BJT transistor. The BJT transistor has two types NPN and PNP, Both are capable of performing amplification and switching operations most commonly we use NPN transistor because NPN transistors have faster electrons mobility and they are easy for designing circuits.

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  • NPN and PNP transistor is the exact opposite of each in terms of their construction and flow of current.
  • In NPN transistor current flows from Collector to Emitter (C to E) whereas in PNP transistor current flows from Emitter to Collector (E to C).
  • NPN transistor is made up of two similar layers of N-type material both are sandwiched on a P-type material.
  • PNP transistor is made up of two similar layers of P-type material and both are sandwiched on an N-type material.
  • In NPN, N- stands for negative charges means electrons in the majority. And in PNP, P- stands for Positive charges means holes in the majority.
  • In terms of their symbols, both NPN and PNP symbols are almost the same the difference is that in NPN transistor arrow points outward and in PNP transistor arrows points inside.
  • In terms of their working, NPN is power ON when the positive charge is applied at the base then current starts to flow from Emitter to collector. And PNP is power ON when there is a low signal (GND) is applied at the base then current starts to flow from Collector to an emitter.
Also Read:
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  1. Introduction to BJT (Bipolar Junction Transistor)
  2. Transistor Configurations, Common Emitter, Base, and Collector Circuits
  3. Transistor Biasing, Fixed base, Collector bias, Emitter Bias, Voltage Divider Bias
  4. Common Emitter Amplifier, BJT Transistor Common Emitter Amplifier
  5. Common Base Amplifier, BJT Transistor Common-Base Amplifier
  6. Common Collector Amplifier, BJT Transistor Common-Collector Amplifier

This all about the difference between NPN and PNP transistor, in this article we learned NPN and PNP transistors differences w.r.t their symbols, constructions, operations. Furthermore, if you feel any query regarding this article feel free to write it below in the comment section or you have any suggestion comment down below, and Thanks for reading our article 🙂

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