The Engineering Projects

Introduction to PNP Transistor

Hey Friends! Hope you are doing great. I am back to give you a daily dose of valuable information so you can always stay ahead of your competitors. I have previously updated the article on NPN transistor that is used for amplification and switching purpose. Today, I am going to unveil the details on the Introduction to PNP Transistor which falls under the category of bipolar junction transistors and comes with three layers i.e. two P-doped layers and one N-doped layer where an N-doped layer exists between two P-doped layers. Main Function: Small current at one terminal is used to control large current at other terminals. Major Charge Carriers:  Holes  These NPN and PNP transistors come with their own benefits based on the nature of the electronic project, however, NPN transistors always deems preferable over PNP transistors because of its quick response due to mobility of electrons while PNP transistors are not preferable for amplification and switching purpose because conduction through mobility of holes deems less useful and beneficial as compared to mobility of electrons. In this tutorial, I’ll discuss each and everything related to this PNP transistor i.e what it does, circuit diagram, applications and everything you need to know. Let’s dive in and explore what is this about and how it is used for the execution of electronic projects.

Introduction to PNP Transistor

• The PNP transistor is a type of bipolar transistor used for amplification and switching purpose and for the designing of the complementary output stage in combination with NPN transistor.
• It comes with three terminals called emitter, base, and collector where small current at the base terminal is used to control large current at other terminals.
• It is a current controlled device also known as sinking device where it sinks current into its base terminal and current flows out of the collector.
• Unlike NPN transistor, current flows from the emitter to collector in this PNP transistor and holes act as a majority charge carriers.

• This transistor comes with same characteristics as NPN transistor but there are some exceptions. In case of PNP transistor, all voltage polarities and current directions will be reversed as compared to NPN transistor. The PNP transistor sinks current into its base while NPN transistor sources current through its base terminal.
• Both NPN and PNP transistors are current controlled devices where conduction is carried out by both charge carriers i.e. electrons and holes, but major charge carriers are electrons in case of NPN transistors. While in case of PNP transistor major charge carriers are holes.
• The PNP transistor is like a combination of diodes combined back to back from cathode sides.

Construction

• This PNP transistor is composed of two P-doped layers and one N-doped layer where N-doped layer represents the base of the transistor while other P doped layers represent emitter and collector respectively.
• The base of the transistor is more negative than the emitter terminal.
• All three terminals in the PNP transistor are different in terms of doping concentration and size.
• An emitter is highly doped and exhibits 100% current of the transistor while a base is lightly doped which is responsible for the transistor action and controls the number of holes in case of PNP transistor.
• While collector is lightly doped and comes in a bigger size as compared to other two terminals and collects the number of holes.

Circuit Diagram

• Following figure shows the circuit diagram of PNP transistor.

• In PNP transistor, a source voltage is applied at the emitter terminal (instead of collector terminal in case of NPN transistor) and load resistor is applied that is used to resist the current in the collector terminal.
• Similarly, a bias voltage is applied at the base terminals and a base resistor is connected to this terminal in order to limit the current flowing through this terminal.
• The emitter is connected to a positive voltage while the base is connected to the negative voltage.

Working

• Similar to NPN transistor, PNP transistor comes with two pn junctions i.e. emitter-base junction and collector-base junction.
• An emitter-base junction is forward biased and shows low resistance while collector-base junction is reverse biased and exhibits high resistance. Steps and process required to make these junctions forward biased and reverse biased are different than NPN transistors.
• Emitter-base junction will become forward biased when a base is negative with respect to the emitter and the voltage at the base side is 0.7 V less than the voltage at the emitter side.
• Similarly, emitter-base junction is made reverse biased when applied collector voltage is negative. In case of PNP transistor, emitter voltage is much larger than collector voltage.
• In order to conduct for PNP transistor, emitter voltage must be more positive as compared to both base and collector.
• The transistor will turn on when there is small current flowing from emitter to base terminal.
• In PNP transistors emitter emits holes as compared to NPN where emitter emits electrons.
• When a proper bias voltage is applied at the base terminal, it gets biased and the holes present at emitter terminal moves to the base terminal where they combine with the electron present at this terminal. This generates the small current at the base terminal.
• The base is very thin so it is very difficult for a base to accept all holes injected by the emitter, as a result, most of the holes leave the base terminal and enter collector terminal.

Matched Switch

• Combination of PNP transistor with NPN transistor is used for designing and development of the power amplifier circuits. Power B amplifiers are the great example of this amplifier circuits where both PNP and NPN transistors are incorporated together to generate high amplification cycle.

• Pair of NPN and PNP transistor used in Class B amplifiers is called complementary or matched switch where PNP transistor conducts for the negative half cycle while NPN transistor conducts for the positive half cycle of the transistor.
• This process is used to generate required power for the loudspeaker in both directions. The resulting power generates at the output current is very high which is then equally shared between matched switch composed of NPN and PNP transistor.

Output Characteristics Curve

• The output characteristic curve of PNP transistor looks identical to that of NPN transistor but there is one exception i.e. it is rotated by 180 degrees.
• The same load line is drawn on the characteristic curve that we drew in case of NPN transistor that mentions the operating points of the transistor.
• The following figure shows the characteristics curve of PNP transistor which is drawn between the output current and collector-emitter voltage and is rotated by 180 degrees where current directions and voltage polarities are reversed. The supply voltage becomes negative for PNP transistor.

• The current gains (alpha, beta) value are much less in PNP transistor as compared to NPN transistor. We can calculate the beta value from the following equation;

Difference between PNP and NPN Transistors

• The PNP transistor is known as sinking device while NPN transistor is known as sourcing device.
• The main difference between PNP and NPN transistor is the proper biasing of the base terminal where current directions and voltage polarities are always opposite to each other.
• In PNP transistor, holes are majority carriers while in NPN transistor electrons are majority carriers.
• The emitter voltage is made more positive as compared to both base and collector in PNP transistor. While collector voltage is made more positive as compared to base and emitter in case of NPN transistor.
• The PNP transistor will be considered ON when there is no current at the base terminal. The NPN transistor will be considered ON when there is enough current present at the base terminal.
• In PNP transistor current flows from the emitter to collector, while in case of NPN transistor current flows from collector to emitter.
• The base is positive in case of NPN transistor while it is negative in PNP transistor.
• When there is enough voltage applied at the base terminal it gets biased in case of NPN terminal while in case of PNP transistor, negative voltage 0.7 V less than emitter voltage must be applied to trigger transistor action.

Applications

• This transistor is used as a switch for electronic signals.
• It is used in amplifying circuits.
• Used as a matched switch in combination with NPN transistor for generating continuous power.
• Current flow involving heavy motors makes use of these transistors.
• Used in robotic applications where current sinking is required.

That's all for today. I hope you have found this article useful. If you are unsure or have any question, you can ask me in the comment section below. I'd love to help you in any way I can. You are most welcome to add anything valuable related to this transistor. Thanks for reading the article.

Introduction to NPN Transistor

Hello Friends! I hope you are well. Today, I am going to give you a detailed Introduction to NPN transistor. In this tutorial, we'll look at the NPN transistor, how it works, circuit diagram, output characteristics curve, and applications. It is a bipolar junction transistor mainly used for current amplification and switching purposes. BJTs (Bipolar Junction Transistor) are divided into two types i.e. NPN transistor and PNP transistor. Both transistors are different in terms of their electrical composition and construction, however, both are used for amplification and switching purposes in one way or the other.

What is NPN Transistor?

• NPN transistor is a bipolar junction transistor(BJT), composed of 3 semiconductor layers in a way that one P-doped layer(Base) is sandwiched between two N-doped layers(Emitter & Collector) and is mainly used for current amplification and fast switching.
• In NPN transistors, the majority charge carriers are electrons and thus conduction is carried out by the flow of electrons from emitter to collector.
• NPN transistor package comes with three terminals named:
  1. Emitter.
  2. Base.
  3. Collector.
• These terminals are used for external connection with the circuit and a small current at the base terminal is used to control the large current at the collector and emitter side. (We will cover it in detail in the working section)

Let's have a look at the symbol of NPN transistor:

NPN Transistor Symbol

• As we use logos to represent companies, similarly in electronics, specific symbols are used to represent components. These electronic symbols prove helpful in designing circuit diagrams especially block diagrams of electronic models.
• Below figure shows the NPN transistor's Symbol:

Now let's have a look at the Construction of NPN Transistor:

Construction of NPN Transistor

• NPN transistor consists of 3 regions, two of them are constructed using N-type semiconductor material while the third one is of P-Type Semiconductor.
• The P-type region is sandwiched between these two N-Type regions.
• So hypothetically, NPN Transistor is constructed by connecting two diodes in opposite directions.
• The equivalent circuit of NPN transistor is shown in the below figure:

• An NPN transistor has two P-N junctions in it, named as:
  1. Emitter-Base Junction.
  2. Collector Base Junction.

Doping Concentration in NPN Transistor

• Impurities are added to Intrinsic(Pure) Semiconductors which increase their conductivity and are called Extrinsic(Doped) Semiconductors.
• In NPN transistors, the Base region is heavily doped, the Emitter is lightly doped while Collector's doping lies in between the Base & Emitter.
• So, in terms of doping concentration from high to low, we have the sequence as follow:

Base > Collector > Emitter

• Moreover, the Base region is constructed using P-type semiconductors, while Emitter & Collector are designed using N-type semiconductors.

Now, let's have a look at the working of NPN transistors:

How NPN Transistor Works?

• The NPN transistor comes with two junctions, called:
  1. Emitter-Base Junction.
  2. Collector-Base Junction.
• The NPN transistor sets in operating condition when an emitter-base junction is forward biased and the collector-base junction is reverse biased and enough current is present at the base terminal. In order to make emitter-base junction forward biased, a positive voltage is applied at the base side and a negative voltage is applied at the emitter side.
• Similarly, in order to make emitter-base junction reverse biased, collector voltage must be kept more positive than base and collector.

Circuit Diagram

Following figure shows the circuit diagram of the NPN transistor.

• We can see from the diagram, voltage and resistive loads are applied at the terminals of the transistor.
• A negative voltage is connected to the emitter while a positive voltage is connected to the base terminals.
• The base is more positive with respect to the emitter.
• The resistive load is applied at the base terminal which limits the current produced in this terminal.
• The positive voltage is applied at the collector terminal and load resistance is applied at this terminal that limits the electrons entering at this terminal.

Working

• The base is responsible for initiating transistor action. When a voltage is applied at the base, it gets biased and draws a small current which is then used to control a large current at the collector and emitter side.
• The base action is considered as an ON-OFF valve that generates current when a proper bias voltage is applied at this terminal.
• The small change in the voltage applied at the base terminal shows a large impact on the output terminals. Actually, the base acts as an input and the collector acts as an output in NPN transistor.
• In case of silicon transistor emitter-base junction draws voltage around 0.7 when there is no voltage at the base terminal, in order to initiate the electron action and put the transistor in running condition, the base voltage must be greater than 0.7 voltage in the case of silicon transistor and 0.3 in case of germanium transistor.
• In the N-side of the transistor which represents emitter, the electrons act as the majority charge carriers which are then diffused into the base when a suitable voltage is applied at the base terminal. These electrons act as minority charge carriers when they enter the base terminal, where they join with holes present in the base. Not all electrons join with the holes present at the base terminal. Some of them join with the holes, and the resulting electron-hole pair disappears. Most of the electrons leave the base terminal and then enter the collector region where they again act as a majority charge carriers.
• When a voltage is applied across the base terminal, the base current is given by;

 

• Collector current is directly related to base current times a constant factor.
• In order to increase the efficiency of the NPN transistor, the base is made very thin and a collector is made thick for two reasons i.e collector can handle more heat and accept more electrons diffused through the base terminal.

Current Gains and Relation between Them

• Current gains play an important role in the amplification process. The common emitter current gain is a ratio between collector current and base current. It is called beta and denoted by ß. It is also known as an amplification factor which defines the amount of current being amplified.
• Beta is a ratio between two currents, so it features no unit. The beta value is always greater than unity and ranges between 20 to 1000 - 20 for high power transistors and 1000 for low power transistors, however, most of the time its value is taken as 50.
• Similarly, a common base current gain is another important factor which is a ratio between collector current and emitter current. It is called alpha and denoted by a. An alpha value ranges between 0.95 and 0.99, however, most of the time its value is taken as unity.
• Following figure shows the relation between two current gains.

• IF alpha = 0.99 then b = 0.99/0.01 = 99.
• An alpha value cannot exceed from unity, because it is a ratio between collector current and emitter current i.e emitter current always remains greater than collector current because it exhibits 100% current of the transistor and is equal to the sum of collector current and base current.

NPN Transistor Configurations

• This NPN transistor can be configured into three configurations called common emitter configuration, common collector configuration, and common base configuration.
• Common emitter configuration is mostly used for amplification purpose where base acts as an input, collector acts as an output while emitter acts as a common terminal between input and output.
• This common emitter configuration acts always operates in a linear region where small current at the base side is used to control large current at the collector side.
• The common emitter configuration used in the electronic circuits always produces inverted output that is highly affected by the bias voltage and temperature. This configuration is an ideal choice for ampliation circuits because it comes with high input impedance and low output impedance and produces the exact voltage and power gain required for amplification purpose.
• During common emitter configuration, transistor always operates between saturation and cut-off region that helps in amplifying the negative and positive cycles of the input signals. If the base terminal is not biased with the proper voltage, only half of the signal would be amplified.

Output Characteristics Curve of NPN Transistor

Following figure shows the output characteristic curve of the NPN bipolar transistor which is plotted between output collector current and the collector-emitter voltage with varying base current.

• As described earlier, there will be no output collector current if the applied voltage at the base terminal is zero. When proper bias voltage above 0.7 V, is applied at the base terminal, it gets biased and draws current that controls and effects the output collector current.
• We can see, Vce directly effects the value of output collector current as long as the applied voltage is 1 V. Above that value collector current no longer remains under the influence of Vce value. In that case, the collector current is widely dependent and controlled by the base current. A small change in the base current and bias voltage would produce a large change in the collector current.
• The load resistor applied at the collector terminal controls the amount of current entering the collector terminals. Keeping in the view of the load resistor and the voltage applied at the collector-emitter terminals, the collector current is given by;

• Straight load line between point A and B falls under active region when an emitter-base junction is forward biased and the transistor conducts where electrons are majority charge carriers.
• The Q point in the graph can be defined by the load line which is actually referred as an operating point of the transistor.
• The output characteristics curve of this NPN transistor is used to describe the collector current when base current and collector voltage is given.
• In order to conduct, collector voltage needs to be more positive than base and emitter.
• It is important to note that, when an emitter-base junction is not forward biased, Ic will be zero, no matter how much voltage is applied at the base terminals. When the emitter-base junction is forward biased and voltage is applied at the base terminal, it draws small current which is then used to control large current at other terminals.

Difference between NPN and PNP Transistors

• Both NPN and PNP transistors are different in terms of electrical construction and layers doping. NPN stands for negative-positive-negative and also known as sourcing device. While PNP stands for positive-negative-positive and also known as sinking device.
• In NPN transistor base is positive as compared to emitter and collector voltage is more positive as compared to both emitter and base. Similarly, in PNP transistor base is negative as compared to emitter and emitter voltage is much larger than collector voltage.
• The voltage polarities and current directions are reversed in both transistors.
• The NPN transistor conducts and initiates transistor action when a positive voltage is applied at the base terminal. The PNP transistor conducts when a negative voltage lower 0.7 V (for silicon) than emitter voltage is applied at the base terminal.
• The NPN transistor uses electrons as majority charge carriers for the conduction while PNP transistor uses holes as majority charge carriers for conduction process.
• In NPN transistor current flows from the collector to emitter while in case of PNP transistor current flows from emitter to collector terminal.
• Both transistors differ in terms of how they are powered on. The NPN transistor powers on when there is enough current present at the base terminal while PNP transistor powers on when there is no current at the base terminal.

Now, let's have a look at the applications of NPN transistor:

Applications of NPN Transistor

NPN Transistor is the most commonly used type of transistor because of its wide range of applications. A few of NPN transistor applications are as follows:

• As NPN transistors are fast switching devices, thus they are used for switching purposes i.e. Pulse Width Modulation.
• NPN transistors are also used as automatic switches in electronics products.
• Because of high current gain, NPN transistors are used for current amplification i.e. small current at input allows heavy current to pass at the output(Ic).
• In embedded computers(i.e. microcontrollers, microprocessors etc.), thousands of transistors are joined together(in SMD form) performing different functions i.e. switching of pins.

Real-Life Applications of NPN Transistor

• Used in logarithmic converters and high-frequency applications.
• Signal processing and radio transmission applications involve NPN transistors.
• Darlington pair circuits make use of this NPN transistor for amplifying signals.
• Used in temperature sensor.
• Push-Pull amplifying circuits, which fall under the category of the classic amplifier circuit, make use of this NPN transistor.
• In small quantities, transistors are used to make logic circuits and in the circuits where amplification is required.

That's all for today. I hope you have got clear what is NPN transistor and why it is used for. If you are unsure or have any questions, you can approach me in the comment section below, I'd love to help you according to the best of my expertise and knowledge. Feel free to keep us updated with your feedback and suggestions, they help us provide you quality content that aligns with your needs and requirements. Thanks for reading the article.

Diode: Definition, Symbol, Working, Characteristics, Types & Applications

Hi Guys! Hope you are doing great. Today, we will have a look at an electronic component named Diode. We will discuss Diode working, Symbol, Applications and characteristics in detail.

A diode is an electronic component, that allows the flow of current in one direction only. It exhibits low resistance in one direction and very high resistance in the opposite direction. Whoever has been a science student, knows about diodes. Although it seems to be a tiny component of a circuit, apparently it is true but it has a lot of complexities or you can say, it's a storm in a teacup.

Diodes are normally used in rectifiers, where they convert AC signals to DC signals. They come with a wide range of applications including power conversion, radio modulation, logic gates, temperature measurements and current steering. I'll try to cover everything related to diodes so let's get started:

Diode Definition

• A diode is a 2-terminal, basic discreet electronic component, made up of semiconductor material, which allows a unidirectional flow of current through it, i.e it only conducts current in one direction.
• A diode is analogous to a uni-directional water flow valve, which allows the water to flow in one direction but restricts it to flow backward.
• Diode consists of two terminals, named:
  • Anode (+).
  • Cathode (-).
• These terminals are connected to two doping regions:
  • P-Type region.
  • N-Type region.
• The P-Type region consists of positively charged ions called Holes, while the N-Type region consists of negatively charged electrons. We will discuss its construction in detail later.

• In a diode, current flows from Anode to Cathode(diode acts as a closed switch), but if the current flows in the opposite direction(i.e. from Cathode to Anode), the diode will block it, so we can say, the diode is acting as an open switch.

Diode Symbol

• The diode symbol and its real package are shown in the below figure:

• The arrowhead in a diode symbol represents the direction of the current flow i.e. current can flow from anode to cathode.

Construction of Diode

Now let's have a look at the construction of a diode:

• A diode is normally made up of a semiconductor material i.e. silicon, germanium, gallium arsenide etc.
• Two crystals of the same semiconductor material(normally silicon) are doped with different types of impurities, one crystal with pentavalent impurity, while the second one with trivalent, to create two types of semiconductor materials named:
  • P-Type Semiconductor: Majority Charge Carriers are Holes(+).
  • N-Type Semiconductor: Majority Charge Carriers are Electrons(-).
• When these two semiconductors are joined/merged together, the free electrons from the N-Type start to move towards the P-Type region, while the Holes start moving towards the N-Type region.
• At the border of these two regions, electrons get combined with Holes and neutralized.
• These neutralized atoms create a layer at the border(of N-Type & P-Type regions) and stop the flow of electrons & Holes. This newly created third layer/region is called the depletion region.
• The depletion region is very small in size and acts as a barrier for the flow of charge carriers(i.e. electrons & Holes) from the N-type to P-type region.
• Below diagram will give you a better idea of Diode construction:

• As you can see in the above figure, we have 3 regions in a final diode, named:

1. N-Type Region: Majority Charge Carriers are Electrons(-).
2. P-Type Region: Majority Charge Carriers are Holes(+).
3. Depletion Region: No Charge(Neutral)

• Two electrically conductive electrodes/probes are connected to these two Regions and are called:
  • Cathode: Connected to N-Type Region.
  • Anode: Connected to P-Type Region.

You must have understood by now, how diodes are constructed? Now, let's have a look at How diode works?

Diode Working

As we discussed in the above section, when two semiconductor materials are merged together, a momentary flow of charge carriers occurs, which results in the creation of a depletion region. This state of the diode is normally termed as Zero Biasing State, as there's no power applied at any terminal. In operational mode, the diode has two other biasing states, named as:

• Forward biased.
• Reverse biased.

Diode as Forward Biased

• The PN Junction created at the center of two regions is very small but it's powerful enough to stop the free electrons from passing through it.
• So, if we could provide some external power to these electrons, they can break this barrier and can make their entry into the P-Type region.
• This external power required to overcome the depletion region is normally termed as a Forward Threshold Voltage of diode.
• This threshold voltage value depends on the semiconductor material used in the diode construction i.e. for silicon it's +0.7V and for Germanium, it's +0.3V.
• So, for a normal diode, if we provide an external power of +0.7V, the electrons will overcome the depletion region and in simple words, the current will start flowing through the diode.
• As you can see in the below figure, the positive terminal of the battery is connected with the anode of the diode and as we will provide a voltage greater than its threshold voltage, the diode will start conducting and is said to be acting as forward biased.
• In forward biasing conditions, an ideal diode has zero resistance, but as I told you earlier, an ideal condition does not exist.

Diode as Reverse Biased

• If the polarity of the applied power is reversed i.e. positive terminal of the battery gets connected with the cathode(-), while the negative terminal gets connected with the anode(+), the depletion region will start to increase.
• In this state, the diode won't allow the current to flow through it and is said to be acting as reverse biased.
• In a reverse Biased state, the diode acts as an open switch.
• The PN junction in reverse biasing offers a very high resistance due to the thickness of the depletion region.
• A diode in ideal condition when reverse biased has infinite resistance.

History of Diode

• Introduced in 1906, the first semiconductor diode was named as Cat's Whisker Diode that was fabricated using mineral crystals.
• Mostly, diodes are designed using silicon because it can handle high temperature, however, germanium is also used when low voltage drop is required.

• When there is no applied voltage across the diode terminals, the diode will not conduct and very thin depletion region exists with no charge carriers around the pn junction of the diode.
• The diode will only conduct when applied voltage at the forward biased condition is greater than the diode built-in potential and it allows the flow of electrons from the cathode to the anode.
• Don't get confused with the arrow sign of the diode pointing from the anode to the cathode. It shows the conventional current flowing from anode to cathode. Conduction will be carried out from cathode to anode when a certain voltage above built-in potential is applied.

 

• A diode will stop conducting when the applied voltage is reverse biased and allows the depletion region to expand, blocking the flow of current. However, when a reverse biased voltage is too large, it allows the small current to flow which is called leakage current. It is too small that most of the time it is ignored while considering the current ratings.
• Similarly, when the reverse biased voltage is too large, it allows the depletion region to expand too much till it collapses, reaching a condition called breakdown, which appears to be very harmful for the quality and operation of the device.
• When we check the value of resistance by multimeter, it shows the low value at one terminal and high value at other terminal which indicates diode is working. It doesn't indicate the actual value of the resistance, instead, it shows the voltage drop across the pn junction.
• For silicon diodes, the forward voltage drop is 0.7 V, which is the voltage required to overcome built-in voltage in order to start the flow of current from cathode to the anode. Similarly, forward voltage drop for germanium is 0.3 voltage which makes it an ideal choice for the applications where low voltage drop is required.
• The voltage drop is highly dependent on the current flowing through the diode, however, it remains constant over a wide range of currents.

Junction Diodes

Diodes are divided into two types based on the formation of the junction between the terminals.

p-n junction Diode

• A pn junction diode is made from semiconductors like silicon or germanium where an N-type region is created with the help of negative charge carriers called n-type semiconductor while the P-type region is created with the addition of positive charge carriers called p-type semiconductors.
• Initially, there is no flow of current between two regions until they are joined together, resulting in a formation of pn junction where movement of electrons starts from N-type semiconductor to P-type semiconductor.

• There exists a region around pn junction where there are no charge carriers called depletion region. When depletion is very thin, indicates a conduction from N-type region to P-type region. When deletion region is very large, indicates no or little flow of current between two regions.
• The diode action takes place around the pn junction. When forward voltage potential more than built-in potential is applied between the diode terminals, it allows the flow of electrons from N-type region to P-type region, while blocking the flow of electrons in reverse order.
• Foward biased mode means the flow of electrons from N type to P type region. Reverse biased mode means no flow of electrons, blocking the current in other direction.

Schottky Diode

• Schottky diode is another type of junction diode where the junction is formed using metal-semiconductor instead of using p-n junction. It is an ideal choice for the applications where high switching speed is required.

Current-Voltage Characteristics

The voltage in V-I curve shows the voltage applied across the diode terminals and current shows the corresponding current obtained as the result of the applied voltage. Based on needs and requirements, the V-I characteristics of the diode can be customized using the suitable semiconductor material and doping concentration of impurities during the manufacturing of the device.

• The depletion region housed between the pn junction shows how the movement of electrons between the two N-type and P-type regions takes place.
• When pn junction is formed, the electrons from N-type region transfers to the P-type region, where they join the holes present in the P-type region.
• When electron combines the hole, the resulting pair disappears and the region around pn junction gets depleted with no charge carriers present. Resulting depletion region around the pn junction acts as an insulator.
• It is important to note, the width of depletion region cannot exceed without limit. When an electron-hole pair is created, it results in the formation of positively charged ion in the N-type region and negatively charged acceptor ion in the P-type region.
• As the formation of electron-hole pair proceeds, it results in the creation of built-in potential where increasing electric field developed around the depletion region, stops the further formation of an electron-hole pair.

Foward Biased Mode

• When the external voltage applied between the diode terminals comes with opposite polarity as the built-in potential, it starts the current flow where depletion region acts as a conductor. In this case, the depletion region formed around the pn junction will be very thin.
• The built-in potential is different for different diodes i.e. 0.7 for silicon and 0.3 for germanium.
• If the external voltage of opposite polarity with more than 0.7 V is applied between the diode terminals in case of a silicon diode, it allows the current to flow from anode to cathode. The diode is considered as "turned on" in this case.
• The voltage above which diode starts conducting through depletion region around the pn junction is called forward threshold voltage which is different than the built-in voltage.

Reverse Biased Mode

• When the external voltage applied between the diode terminals comes with the same polarity as built-in potential, it allows the depletion region to expand and stops the flow of current where depletion region acts as an insulator.

Types of Diodes

There are many types of diodes available in the market which are mainly used for the customization of voltage or current. Most of the pn junction diodes are made from silicon and germanium. Before the inception of these power diodes, selenium was used to manufacture the diodes.

Selenium diodes come with low efficiency as compared to silicon diodes, because high forward voltage around 1.4 or 1.7 V is required to start conducting around the pn junction, resulting in the need of much larger heat sink. Following are the most commonly used diodes in the electronic devices.

LED Diodes

• These diodes are made from the crystalline substance that emits light in different colors like red blue green or orange, depending on the crystalline material used in the diode.
• These diodes emit incoherent, narrow-spectrum light, capable of producing wavelengths in the wide range.
• Most of the LED diodes are low-efficiency diodes, which make them an ideal choice for the signal applications. LED diodes are also used in the formation of opto-isolator.

Avalanche Diodes

• These diodes are very identical to Zener diodes, where they start conducting in the reverse direction when reverse bias voltage becomes greater than break down voltage. These diodes come with an ability to break down at a certain voltage, without destroying them completely.
• Both Zener and Avalanche diodes are quite similar with respect to their mode of operation with one practical difference i.e. both didoes exhibit temperature coefficient with opposite polarities.

Zener Diodes

• Zener diodes, also termed as reverse breakdown diodes, are the diodes that conduct in reverse bias condition.
• Zener breakdown effect occurs at a very specific voltage, making them suitable for use as a precision reference voltage.
• In reference circuits, temperature coefficient balancing can be achieved by using a combination of zener diodes and switching diodes.
• Both avalanche and zener diodes fall under the category of breakdown diodes and electrically they response quite similar with one exception i.e. zener diodes operate with a breakdown voltage below 5 V, while avalanche diodes operate with a breakdown voltage above 5 V.

Crystal Diodes

• Crystal diode, also known as Cat's Whisker diode, is point contact diode which is not easily available in the market. This diode comes with a thin metal, known as an anode, and semiconductor crystal, known as a cathode.

Photodiodes

• Photodiodes are composed of semiconductor materials that are light sensitive, making them an ideal choice for solar cells and optical communications.
• These diodes are mostly available in single diode package, however, single dimensional or double dimensional array combination is also widely available.

Applications

Diodes allow the current to flow in one direction which makes them suitable for most of the applications where current controlling is prerequisite. Following are the major applications of the diodes.

ONE. Logic gates are designed using diodes with other electronic components.

TWO. Diodes are also used as a waveform clipper, where they clip the negative or positive peak of the signal in order to attain specific voltage.

THREE. Didoes are helpful for temperature measuring because the forward voltage drop across them is very sensitive to temperature. Most of the diodes come with negative temperature coefficient which remains constant above 20 Kelvin.

FOUR. Diodes are widely used for the demodulation of amplitude signal. The amplitude of AM signal is directly proportional to the original audio signal and comes with positive and negative peaks of the carrier wave. The diode is used to rectify the AM radio signal, resulting in only positive peaks of the carrier wave. A filter is applied in order to extract the audio signal from radio carrier wave, which then produces sound waves when applied to the amplifier.

FIVE. Rectifiers are made from diodes which widely replace the commutator for converting AC signal to DC signal.

SIX. Some electronic circuits are very sensitive and show high spikes in the voltage during the execution of the project. These diodes are used to prevent the circuits from high voltages spikes which appear to be very damaging, if not controlled properly, in the early stages.

That's all for today. I hope you have found this article useful. If you're unsure or have any question, you can approach me in the comment section below. I'd love to help you according to best of my expertise in any way I can. Feel free to keep us updated with your suggestions, they help us to provide you quality work that resonates with your needs and demands. Thanks for reading the article.

Introduction to BJT (Bipolar Junction Transistor)

Hey Guys! Hope you are doing great. Today, I am going to discuss the details on the Introduction to BJT (Bipolar Junction Transistor). It is an electronic component mainly used for amplification and switching purpose. As the name suggests, it is composed of two junctions called emitter-base junction and collector-base junction. Don't confuse BJT with regular transistors. A transistor is a semiconductor device, comes with three terminals that are used for external connection with electronic circuits. A transistor is termed as a trans resistor which is used as switch or gate for electronic signals. Small signals applied between one pair of its terminals are used to control much larger signals at the other pair of terminals. Actually, transistors are divided into two categories called unipolar transistor and a bipolar transistor. Bipolar junction transistor uses two charge carries i.e. electrons and holes while unipolar transistor like FETs (Field Effect Transistors) uses only one charge carrier. I hope you are aware of another type of transistors called MOSFET. I'll try to cover each and everything related to this bipolar junction transistor, so you find all information at one place. Let's get started.

Introduction to BJT

• Introduced in 1948 by Shockley, BJT is an electronic component mainly used for switching and amplification purpose.
• It is composed of three terminals called emitter, base, and collector, denoted as E, B and C respectively.
• This transistor comes with two PN junctions. The PN junction exists between emitter and base is called emitter-base junction and the PN junction exists between collector and base is called collector-base junction. Emitter-base junction is forward biased and the collector-base junction is reverse biased.
• In the start BJTs were made from germanium, however, recent transistors are made from silicon.
• BJT comes in two types called NPN transistor and PNP transistor.
• It is a bipolar device where conduction is carried out by both charge carriers i.e. electrons and holes. The number of electrons diffused in the base region is more the number of holes diffused in emitter region. Electrons behave as a minority carrier in the base region.
• Under normal conditions, when the emitter-base junction is forward biased it allows the current to flow from emitter to collector. When a voltage is applied at the base terminal, it gets biased and draws current, which directly affects the current at the other terminals.
• BJT is called a current controlled device where small current at the base side is used to control the large current at other terminals. All three terminals of the BJT are different in terms of their doping concentrations. The emitter is highly doped as compared to base and collector.

• The collector is moderately doped and its area is larger as compared to emitter area, allowing it to handle more power.
• When a voltage is applied, the majority of electrons from emitter are diffused into the base where these electrons act as minority charge carriers, making the holes in the base region majority charge carriers.
• As the base is very thin and lightly doped it cannot hold the number of electrons for too much time, allowing the electrons to diffuse from base to collector.
• Making a slight change at the voltage applied at the base-emitter terminals can cause a significant change at the current between emitter and collector terminals.
• This is the process used for amplification purpose.
• When the emitter-base junction is not forward biased the amount of current at the base and collector terminal is zero, no matter how much voltage is applied at the base terminal.
• Common-Emitter current gain is a term mostly used for BJTs. It is a ratio between collector current and base current. Similarly, a common-base current gain is defined as a ratio between collector current and emitter current. Most of the time its value is taken as unity.
• Construction of BJT is not symmetrical in nature. The lack of symmetry of BJTs is due to the difference in doping concentration between the terminals.
• Generally, BJTs are operated in forward-biased mode. Interchanging the emitter and collector allows the forward biased mode to change to reverse biased mode. This interchange causes a wide impact on the values of current gains, making them much smaller as they are in forward-biased mode.
• The mode of operation where an emitter-base junction is forward biased and the collector-base junction is reverse biased is called active region.

Types of BJT

BJTs are divided into two types based on the nature and construction of the transistor. Following are two main types of the BJT.

NPN

• NPN (negative-positive-negative) is a type of BJT where a P-doped layer of semiconductor exists between the two layers of N doped material.
• The P doped region represents the base of the transistors while other two layers represent emitter and collector respectively.
• NPN transistors are also called minority carrier devices because minority charge carriers at the base side are used to control large current at other terminals of the transistor.
• The current moves from an emitter to the collector where electrons act as a minority carrier at the base side.

PNP

• PNP (positive-negative-positive) transistor is a type of BJT where N doped semiconductor layer which acts as a base, is housed between the two layers of P doped material.
• The base uses small base current and negative base voltage to control large current at the emitter and collector side and voltage at the collector side is larger than the voltage at the base side.
• In PNP transistor current direction and voltage polarities are reversed as compared to NPN transistors.
• PNP transistors work in a similar way like NPN transistor with some exception i.e. holes are diffused through the base from an emitter and are collected by the collector.
• This transistor is rarely used for applications as conduction carried out by the movement of electrons is considered fast and holds more value as conduction by movement of holes.

Regions of Operations of BJT

Bipolar junction transistors come with different regions of operation. These modes of operations set a tone for current flowing from emitter to collector.

Forward Active Mode

• BJT comes with two junctions called emitter-base junction and collector-base junction. Emitter-base junction is forward biased and the collector-base junction is reverse biased.
• For amplification purpose, most of the transistors come with high common emitter current gain which shows the exact current and power gain required for amplification purpose.
• The collector-emitter current is largely dependent on the base current where small current at the base side is used to control the large current at the emitter and collector side.

Reverse Active Mode

• By interchanging the emitter and collector, transistor goes from active mode to reverse active mode.
• Most of the transistors are designed to afford high current gain, but reversing the role of emitter and collector makes the current gain very small as compared to forward biased region. This type of mode is rarely used unless a failsafe condition is required.

Saturation

• BJT exhibits saturation mode when both junctions are forward biased. This mode of operation is referred as a closed circuit which allows a large amount of current flowing from emitter to collector side.

Cut-off

• When the emitter-base junction is not forward biased, the transistor is said to have in the cut-off region where collector current and base current will be zero, no matter how much voltage is applied at the base terminal.

Three Basic Configurations of BJT

BJT is a current controlled device which is mainly used for amplification and switching purpose. There are three ways to connect this device with external electronic circuits called: 1. Common Base Configuration 2. Common Collector Configuration 3. Common Emitter Configuration The nature of the current being controlled at the output is different for different configurations.

Common Base Configuration

• Common base configuration is a configuration where the common base is shared between input and output signal.
• Voltage is applied at the emitter-base junction and corresponding output signal is obtained at the output across the base-collector junction.
• The base voltage is connected to some reference voltage or can be grounded in some cases with the intention of making common base between input and output signals.
• Following figure shows the circuit diagram of common base configuration.

• Current at the emitter side is quite large, where electrons are diffused into the base terminal. These electrons make a pair with some holes present in the base, while most of them leave the base and are collected by the collector.
• This type of transistor comes with remarkable high voltage characteristics which don't make it an ideal choice for many applications. In this configuration, an output and input voltage is in line with each other. The input characteristics of this transistor are quite identical to forward biased diode while output characteristics are similar to a regular diode and come with a high output to input resistance ratio.
• Common base current gain is a very important factor used in this configuration which is a ratio between collector current and emitter current. It is denoted by a alpha.
• a = Ic/Ie
• The alpha value ranges between 0.95 to 0.99, however, most of the time its value is taken as unity. High-frequency response of common base configuration makes it an ideal choice for single stage amplifier.

Common Collector Configuration

• This configuration is also known as voltage follower where the input is applied at the base terminal and output is taken from emitter terminal.
• This configuration is mainly used for impedance matching as the input impedance of this configuration is very high while output impedance is very low.
• Common collector configuration is termed as non-inverting amplifier where output signal and an input signal are in phase with each other.
• The current gain of this transistor is very large because the load resistance is at the receiving end of both collector current and base current, making it a suitable for amplification purpose.
• Hence very little voltage gain, around unity, can help in producing very large current gain.
• Following figure shows the circuit diagram of common collector configuration.

Common Emitter Configuration

• This configuration is widely used in transistor based amplifier, where an input signal is applied between emitter and base while the output is taken from emitter and collector.
• This configuration comes with highest current and power gain which makes it an ideal choice for amplification. Input impedance is connected to forward biased PN junction which shows low value while output impedance is connected to reverse biased PN junction which shows high value.
• Most of the transistors generally come with common emitter configuration because this exhibits the ideal power and current required for amplification purpose.
• Common emitter configuration is termed as inverting amplifier circuit where an input signal is out-of-phase with the output signal.
• Following figure shows the circuit diagram of common emitter configuration.

 

• The common emitter current gain of this transistor is very large as compared to a current gain of common base configuration which is a ratio between collector current and base current. It is denoted by ß beta which is the measure of current being amplified.
• ß = Ic/Ib
• Output current at the collector and emitter side is highly dependent on the current at the base side.
• Current at the emitter side is the sum of current at the base and collector side because emitter side is highly doped as compared to base and collector.
• Ie = Ib + Ic
• When the voltage is applied at the base terminal it triggers the electrons reaction which forces the electrons to move towards the collector side.
• Any small change at the voltage applied at the base terminal results in a very large change at the current obtained at the collector side.

Pros of BJTs

• Bipolar junction transistor comes with a large amplification factor.
• This type of transistor provides a better voltage gain.
• This transistor comes with a capability of operating in four regions i.e active region, reverse mode, saturation and cut-off region.
• BJT provides a better responese at higer frequiencies.
• BJTs also act as a switch.

Cons of BJTs

• BJT is very sensitive to heat and produces noise is some cases.
• The switching power of BJTs is very low as compared to unipolar transistors like FETs.

Applications

• BJTs come with two major applications called amplification and switching.
• They are the building blocks of most of the electronic circuits, especially where audio, current or voltage amplification is required.
• NPN transistors are preferred over PNP transistors for amplification purpose because conduction carried out through mobility of electrons is better than conduction through mobility of holes.

That's all for today. I have tried my best to break down each and everything related to BJTs so you can digest the main concept easily. In case you are unsure or have any question you can ask me in the comment section below. I'd love to help you according to best of my expertise. Feel free to keep us updated with your valuable suggestions, they allow us to give you quality work. Thanks for reading the article.

What is MOSFET? Definition, Full Form, Symbol & Working

Hey Guys! I hope everyone's fine. Today, we are going to have a look at What is MOSFET? We will cover MOSFET Definition, Full Form, Symbol, Working & Applications in detail.

MOSFETs are commonly used in many electronic applications. A number of MOSFETs are added in tiny memory chips or microprocessors that are widely used in cell phones and laptops. It is a voltage-controlled device that is used for amplification and switching purposes. I'll try to touch every area related to MOSFET. Let's get started.

What is MOSFET?

• MOSFET is an advanced type of FET, manufactured with controlled oxidation of semiconductor, having 4 Terminals, named:
  • Drain(D)
  • Gate(G)
  • Source(S)
  • Body(B)

where,

• Gate(G) Terminal is practically insulated from the entire assembly by a thin layer of Silicon-oxide(SiO2).
• Body(B) Terminal is connected internally with Source(S) Terminal & thus the MOSFET package consists of 3 pins.

• The below figure shows the MOSFET package, construction & symbol: (we will discuss them in detail below)

MOSFET Full Form

• MOSFET stands for "Metal-oxide Semiconductor Field Effect Transistor".

MOSFET Symbol

• Although MOSFET has 4 terminals, but as I have mentioned before, the 4th terminal is internally connected with the Source terminal & thus the package consists of 3 Pins, so as the MOSFET Symbol.
• MOSFET symbols are shown in the below figure:

Why MOSFET?

• Unlike BJT, MOSFET requires almost no input current & controls heavy current at the output.
• MOSFETs are quicker in operation than FETs, thus used in fast switching applications.
• FET has high drain resistance, while it's too low in MOSFET.

History of MOSFET

• MOSFET laid the foundation of modern electronics back in 1959 when it was invented at Bell lab by Mohammad Attala and Dawon kahng.
• MOSFET was presented to the world in the 1960s with a few tweaks in the original version of the device.
• In the 1960s the invention of MOSFETs led to rapid exponential growth of the semiconductor world, it enabled the use of semiconductors in integrated circuits and microcontroller units.
• MOSFET is compact and easy to use, which is why it is always in demand for mass production.

MOS Revolution

• The evolution and development of MOSFET led to a revolution in electronics which is labeled as the MOS revolution or MOSFET revolution.
• The birth of the Metal Oxide Semiconductor Field-effect transistor was regarded and cherished as the birth of modern electronics.
• MOSFET is one of the most widely mass-produced technologies of this era. Can you imagine the count of MOSFETs manufactured to date? By 2018 it was 13 Sextillion, unbelievable! Isn’t it?

MOSFET Construction

• Let's understand the construction of N-type MOSFET: In N-type MOSFET, two highly doped N regions are diffused into a single lightly-doped P substrate.
• Silicon Oxide(SiO2) layer is placed over Gate Terminal to create the insulation.
• Aluminum Probes are used for connecting terminals i.e. Gate, Drain & Source to respective regions.
• Silicon oxide(SiO2) layer is the main difference between FET & MOSFET and thus MOSFET is sometimes referred to as "FET with Insulated Gate" or "IGFET(Insulated Gate Field Effect Transistor)".
• Because of this oxide layer, MOSFET acts as a voltage controlled IC i.e. voltage at Gate Terminal decides the conductivity between drain and source.
• The conduction path between Source(S) and Drain(D) is called channel & its width is controlled by the Gate(G) voltage in MOSFET.
• MOSFET is a unipolar device i.e. conduction of current is carried out by the movement of either electrons or holes(majority charge carriers).
• N-Channel MOSFET internal Construction is shown in the below figure:

 

Types of MOSFET

MOSFETs are further divided into two types. MOSFET types are as follows:

1. N-Channel MOSFET.
2. P-Channel MOSFET.

Let's understand these MOSFET types, one by one:

N-Channel MOSFET

• In N-Channel MOSFET, a single P-layer is present between two N-layers & current flows because of negatively charged electrons(termed as majority charge carriers).
• Below figure shows the symbol, construction & block diagram of N-channel MOSFET:

P-Channel MOSFET

• In P-Channel MOSFET, single N-layer is present between two P-layers & current flows because of positively charged holes(termed as majority charge carriers).
• Below figure shows the symbol, construction & block diagram of P-channel MOSFET:

MOSFET Working Principle

In order to understand the working principle of MOSFET, we have to first understand its operational modes. Depending on the polarity of Gate Voltage, MOSFET operates in two modes, named:

1. Enhancement Mode.
2. Depletion Mode.

MOSFET Enhancement Mode & Depletion Mode

Let's take the example of an N-type MOSFET:

• If a positive voltage is applied at the Gate Terminal of N-type MOSFET, it starts conducting by creating a bridge between Drain & Source and termed as acting in Enhancement Mode.
• When a positive voltage is applied at the Gate terminal, the surface below the oxide layer starts attracting electronics while repelling holes.
• Hence, electrons get accumulated below the silicon oxide layer.
• As we increase the voltage at Gate Terminal, more electrons get attracted & thus conduction increases in N-Type MOSFET.
• If we reverse the voltage at Gate Terminal, N-type MOSFET will repel electrons and attract holes, thus the connection between Drain & Source will break & MOSFET is said to be in Depletion Mode.
• Both Operating Modes of N-Type MOSFET is shown in below figure:

MOSFET Characteristics

• In the composition of enhancement MOSFET, there must be minimum input gate-source voltage is applied to the gate before it starts conducting, this minimum voltage is called threshold voltage.
• In order to conduct these enhancement amplifiers, the gate-source voltage Vgs must be greater than the threshold voltage.
• Drain current Id will increase by increasing the forward biasing of MOSFET, making them suitable for efficient amplifier circuits.
• When we apply a fixed voltage between the drain and source Vds, we can plot the values of drain current Id for different values of the voltage across gate and source Vgs.

• These VI characteristics show the transconductance of the MOSFET. This transconductance is the ratio between the output drain current to the input gate-source voltage.
• For a fixed value of Vds, the slope of transconductance can be found as

gm= ?Id/?Vds

• This ratio is termed as transconductance which is a short form of "transfer conductance". The SI unit of transconductance is Siemens which is ampere per volt.
• The voltage gain of this MOSFET increases with the increase in transconductance and value of the drain resistor.
• At Vgs=0, N-Type enhancement MOSFET acts like an open switch or normally off, because field-effect won't be able to open the N-Type channel around the gate.
• Thus transistor will fall under the "cut-off" region at this point. The OFF condition of the MOSFET is represented by the dotted line, unlike the depletion region which shows a continuous line, showing the conduction region of the transistor.

• As we apply gate-source voltage Vgs at the gate terminal, it will start to conduct in the region between source and drain.
• The voltage at which transistors start conducting is known as threshold voltage and is represented by Vth.
• As we increase the gate-source voltage it will allow the conducting channel to go wider and ultimately increases drain current Id.
• It is important to note that the gate never conducts as it is practically isolated from the conducting channel between source and drain. MOSFET encompasses high impedance which is useful in many electrical amplifying circuits.
• If the threshold voltage is greater than gate-source voltage, then the channel will not conduct, it will only conduct when threshold voltage will be less than gate-source voltage Vgs.
• In the conduction or saturation region drain current can be calculated as
• Id= K(Vgs-Vth²)
• It is important to note that values of the threshold voltage Vth and K(conduction parameter) are different for different eMOSFET, these values don't vary physically as they come by default during the composition of the material from which transistors are made.
• It is clear from the figure above that graph on the right side starts as a parabola and then it becomes linear, and it gives the slope of the characteristic curve that increases with the increase in drain current for a fixed value of drain-source voltage Vds.
• In order to put the MOSFET in ON state, the gate of the transistor must be biased from its given threshold level.
• Biasing of gate terminal can be achieved using two different methods i.e. Zener diode biasing, and drain feedback biasing. Before biasing you must take one point into consideration that gate voltage must be greater than source by a value greater than the threshold voltage.

MOSFET as a switch

• It is the most basic and widely known application of the MOSFET.
• Consider the following circuit diagram, an N channel MOSFET is used in the enhanced mode to operate the lamp.
• When the positive voltage VGS is applied to the gate of the MOSFET, a channel is established and the lamp is turned ON.

• Similarly, when the gate voltage is zero the lamp turns off.
• MOSFET can only work as an analog switching circuit if it operates between the cut off region when the gate-source voltage is zero up to the saturated region where the VGS becomes saturated, you can go through the complete process by studying the characteristics curve of the MOSFET we have discussed in the earlier section.
• The circuit which we are discussing has a very small amount of resistive load, if you want to protect your MOSFET from overloading you need to connect it to a relay or a diode. If you are not providing enough protection to your MOSFET, you would eventually damage it.

Comparison of MOSFET with Other Transistors

MOSFET was practically designed to make amends in the performance of Junction Field-effect Transistors because they had very high drain resistance, a very slow processing speed, and they were a bit noisy as well. We have been discussing transistors lately and we are done with the detailed outlook of other transistors such as bipolar junction transistor and field-effect transistor as well, so let us compare all the three main types to summarize the concepts. It would help you revise the previously learned concepts as well.

MOSFET vs BJT

• The major difference between BJT and MOSFET is that BJT is a bipolar device in which conductivity is carried out by the movement of both electrons and holes while MOSFET is a uni-polar device in which conduction is carried out by the movement of electrons or holes.
• The three terminals in BJT called emitter base collector are analogous to MOSFET three terminals called source gate and drain respectively.
• Another area where MOSFET differs from BJT is that there is no direct connection between the gate and conducting channel of source and drain, unlike BJT where a small current at the base side is used to control the large current at the emitter and collector side. That's the reason MOSFET is also named IGFET (Insulated Gate Field Effect Transistor).
• BJT is a current-controlled device meanwhile MOSFET is a voltage-controlled device, for a better understanding you can read the article to know how a MOSFET is a voltage controlled device.
• MOSFET is preferably used in analog circuits and BLDC motors but bipolar junction transistors are not the first choice in this regard.
• We mainly use BJT for performing low current functions on the parallel lines MOSFET are implied in high power applications, don't worry we will discuss the appliances of MOSFET in later sections.

MOSFET vs JFET

Both MOSFET and JFET belong to the same family of field-effect transistors.

• MOSFET has four components meanwhile the JFET has three components, three components namely the base source and drain are the same meanwhile the only different component is the Body of the MOSFET.
• MOSFET has a higher input impedance than the JFET.
• MOSFET has higher drain resistance than JFET because of the already established conduction channel of MOSFET.
• MOSFET make less noise than the JFET
• JFET is less costly and easy to manufacture because of the absence of a metal oxide layer that is present in MOSFET.
• MOSFET can easily be damaged due to low input capacitance meanwhile a higher input capacitance saves the JFET from immediate damage.
• JFET has a higher gate current than the MOSFET.
• MOSFET can work in two modes, depletion-mode as well as enhancement mode, on the other hand, JFET only works in depletion mode.

MOSFET vs IGBT

• IGBT is the insulated Gate Bipolar Transistor meanwhile MOSFET is the metal oxide semiconductor field-effect transistor
• IGBT is the combination of the bipolar junction transistor with the MOSFET, meanwhile, the MOSFET is the true transistor.
• MOSFET are not tolerant to electrostatic discharges meanwhile an IGBT is highly stable in this regard.
• The IGBT is tolerant of overloading meanwhile a MOSFET is susceptible to damage because of overloading.
• IGBT is used in high power applications, on the parallel lines, the MOSFET has a relatively lower capacity to deal with such high power applications like IGBT.

MOSFET Review

• MOSFET is a type of FET that is a unipolar device i.e. single charge carriers are responsible for the conduction between source and drain.
• The voltage applied at the gate side is used to control the current flowing through conducting channel between source and drain.
• MOSFET is a voltage-controlled device, unlike BJT which is a current-controlled device.
• Practically, the gate of the MOSFET draws no current. However, a small amount of initial current is needed to charge the capacitance of the gate terminal.

MOSFET Applications

• MOSFET is mostly used as an electronic automatic switch in both analog & digital circuits.
• It is widely used in applications where high amplification is required.

That's all for today. Hope you have got a clear idea about MOSFET. If you have any questions you can ask me in the comment section below. I'll try my best to resolve your query as soon as possible. Your feedback and suggestion will be highly appreciated. It will allow us to give you quality work based on your needs and expectations. Stay tuned!  

Introduction to JFET

Hello Guys! I hope you are doing great and having fun. I am back to give you a daily dose of knowledge that will enhance your learning skills and put you ahead of others. Today, I am going to give you details on the Introduction to JFET. It is a Junction Field Effect Transistor that consists of three terminals named drain, source and gate. It comes in two configurations called the P-Type channel and the N-Type channel. I'll give you brief details on JFET and try to cover as many aspects as possible. Let's get started:

Introduction to JFET

• JFET (Junction Field Effect Transistor) is a uni-polar voltage-controlled device that consists of three terminals called drain, source and gate.
• Unlike bipolar junction transistors which are bipolar current-controlled devices in which a small amount of base current is used to control a large amount of current at the collector and emitter side, JFET is a uni-polar voltage-controlled device in which voltage applied to the gate terminal allows the current to flow through JFET, resulting in input applied voltage equals to the current flowing through the transistor.

• In JFET, gate is always negatively biased as compared to source.
• As compared to bipolar junction transistors, JFET are uni-polar because current carriers in case of JFET are either electrons or holes while bipolar junction transistors are operated by the movement of both electrons and holes.
• The operation of JFET depends on the electric field created by input applied voltage, hence it is called Field Effect Transistor.

• JFET can be classified into two types on the bases of their operation i.e. N-Type and P-Type JFET.
• In JFET, current carrying path between drain and source is called channel which contains no pn-junction. Channel can be made up of P-Type or N-Type semiconductor.
• Current flowing through this channel widely depends on the input voltage applied to the gate terminal of JFET.
• Field effect transistors generally comes in two types JFET (Junction Field Effect Transistors) and MOSFET( Metal Oxide Semiconductor Field Effect Transistors)
• As stated earlier, JFET contains no pn-junction, instead it comes with channel that consists of N type or P type semiconductor that passes between source and drain terminals of JFET.

JFETs are classified into two main configurations.

1. N-Type Configuration
2. P-Type Configuration

1: N-Type Configuration

• In N-Type configuration current flowing through the channel is negative i.e. current flow is carried out by the flow of electrons which are also termed as donor impurities.

• The measure of conductivity of electron in N-Type configuration is much higher than the holes in P-Type configuration, because electrons come with high level of mobility than holes. Hence, in terms of conductivity, N-Type configuration is more efficient than P-Type configuration.
• Channel is a conducting path between drain and source. Within this channel, there lies a third terminal called Gate at which input voltage is applied that is used to control the current flowing through the JFET.
• As channel is resistive in nature, resulting in creating the voltage gradient which becomes less positive as we move from drain to source terminal. This less positive voltage makes drain terminal high reverse biased and source terminal low reverse biased. This bias creates a depletion region whose width is directly proportional to the bias itself.
• The current carrying path between source and drain is controlled by the voltage applied to the gate terminal. In an N-Type configuration of JFET this gate voltage is negative while in case of P-Type configuration it is positive.
• It is important to note that gate current in reverse biased condition in the JEFT is practically zero, while base current in Bipolar junction transistor always comes with a value greater than zero.

N-Type Channel Biasing

• Following is the figure shows N-Type semiconductor with P-Type material which forms the reverse biased PN-junction that creates a depletion region around the gate terminal of JFET.

• Depletion region will be created in the absence of external voltages. JFET are also termed as depletion mode components.
• The depletion region will create a voltage gradient of some thickness which ultimately limits the flow of current, hence results in increasing the overall resistance of FET.
• It is clear from the figure above that most part of depletion region lies between the gate and drain terminals which least part lies between the gate and source terminals which means resistance between gate and drain terminal appears more than the resistance between gate and source terminals.
• In the absence of external input voltage at gate and small voltage at the drain and source Vds allows the saturation current to flow between drain and source.
• The amount of current flowing through the pn-junction will be restricted by the depletion region around the pn-junction.
• It is important to note, if we apply negative voltage at the gate and source Vgs terminals, it will cause the depletion region to grow which ultimately restricts the flow of current, hence results in decreasing the overall conduction of transistor.
• If the voltage applied at the gate terminal Vgs appears to be more negative, it will allow the depletion region to increase and results in decreasing the overall width of channel. The moment comes when applied voltage at gate terminal appears to be negative to the point that will squeeze the channel and won't allow a fraction of current to flow between source and drain terminals.
• The negative voltage applied to the gate terminal at which no current flows between drain and source terminals is called "Pinch-off Voltage".
• In pinch off region negative voltage at the gate terminal Vgs controls the overall conductivity of the channel. This is the reason JFET are called voltage controlled devices.
• Voltage appears at the gate terminal must not be positive, otherwise it will make resistance zero and allows the current to flow between gate terminal instead of source terminal. Positive voltage at the base terminal can damage the transistor at large.

2: P-Type Configuration:

• In P-Type configuration current flowing through the channel is positive i.e. current flow is carried out by the flow of holes which are also termed as acceptor impurities. Both N-Type and P-Type configurations come with same characteristics with some exceptions.

1. Current carriers in N-Type configuration are electorn, hence current appears to be negative
2. Current carriers in P-Type configuration are holes, hence current appears to be positive.
3. Biasing voltage in P-Type configuration comes with reverse polarity.

• The voltage applied at the gate terminal is used to control the current flowing between source and drain. As JFET is a voltage controlled device and no current flows through gate terminals Ig=0. Hence in that case, current flowing out from source terminal will be equal to the current flowing into the drain terminal i.e. Is=Id

 

V * I Curves of N-Channel JFET

Following figure depicts the four region of operation of JFET.  

• Ohmic Region: Region is called ohmic region when Vgs=0. In this region JFET operates like a voltage controlled resistor.
• Pinch off  or Cut-off Region: It is region at which voltage applied to the gate is negative to the point which causes depletion region to increase and allows the current carrying width to decrease till it disappears, resulting in maximum resistance to appear and current flowing through the channel will be zero.
• Active or Saturation Region: The region that is controlled by gate voltage Vgs and where JFET becomes good conductor is called active region. Vds has no effect on active region.
• Breakdown Region: Region is termed as breakdown region where voltage between source and drain appears to be maximum to the point where it breaks the resistive channel and allows the current to flow between the channel.

V * I Curves for P-Type JFET

• The curves for P-Type configuration appear to be same with one exception i.e. Increase in positive voltage at the gate terminal will decrease the current at the Drain terminal Id.

Formula for Drain Current and Drain-Source Channel Resistance

• Drain current at the saturation region can be calculated as follows:

Id= Idss * [ 1 - Vgs / Vp ]

• Id lies between zero to Idss.
• Similarly, if we know drain source voltage Vds and drain current Id, we can calculate the drain-source channel resistance.

Rds = ?Vds / ? I d = 1 / gm

• Here gm represents the "transconductance gain"

Different Modes of Operation of FETs:

FETs can be classified into three different modes of configuration.

1. Common Source Configuration
2. Common Gate Configuration
3. Common Drain Configuration

1: Common Source Configuration CS:

Common source configuration is an analogous to the common emitter configuration in the bipolar junction transistors. In this configuration input voltage is applied to the gate terminal and output we get is from the drain terminal. This mode of operation comes with amplified voltage and high impedance, hence it is mostly used in high audio frequency amplifies. As this is an amplifying circuit, it allows the output to be diverted 180º from its input.

2: Common Gate Configuration CG:

Common gate configuration is an analogous to the common base configuration in the bipolar junction transistors. In this configuration input voltage is applied to the source terminal and output appears at the drain terminal while gate is connected to ground. In this configuration impedance will be low as compared to common source configuration. This configuration is mostly used in high frequency and impedance matching circuits. Unlike common source configuration, here "output signal is in phase with the input signal"

3: Common Drain Configuration CD:

Common drain configuration is an analogous to the common collector configuration in the bipolar junction transistors. In this configuration input voltage is applied to the gate and output signal is collected from the source. It is important to note there is no signal applied to the drain terminal. Vdd simply depicts the bias voltage. Similar to common gate configuration, here "output signal is in phase with the input signal"

Comparison between BJT and JFET

• • Both, bipolar junction transistors and uni-polar field effect transistors encompass same characteristics with some exceptions.
  • BJT are bipolar devices i.e. they are operated by the movement of both electrons and holes. JFET are unipolar devices i.e. they are operated by the movement of either electrons or holes.

• As compared to Bipolar junction transistors, JFET comes in much smaller form and can be used in many tiny electronic chips.
• One major feature that differentiates between bipolar junction transistors and JFET is the input impedence. It is very high in case of JFET while it appears very low in bipolar junction transistors.

Applications

• JFET are widely used in many electronic appliations. They are mainly used for amplification purpose.
• JFET are used to obtain high frequency audio signal.
• They are useful for obtaining impedance matching circuits.

That's all for today. I hope you have got a clear idea about JFET. However, if still you feel any doubt or query in understanding the concept of JFET, you can ask me in the comment section below. I'll be glad to help you in this regard. Your feedback and suggestion will be highly appreciated. It will help us give you quality work that resonates with your needs and expectations. Stay tuned!