File Name: working of pnp and npn transistor .zip
A bipolar junction transistor BJT is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor , uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between two other terminals, making the device capable of amplification or switching.
- Bipolar junction transistor
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- Working of NPN Transistor
- Differences between NPN & PNP Transistors and their Making
Transistors are one of the very important components used in electronic circuit constructions.
Bipolar junction transistor
Transistors are one of the very important components used in electronic circuit constructions. These humble components can almost be found everywhere; from simple relay driver circuits to complex motherboard circuits, transistors prove their presence.
In fact, your microcontrollers and microprocessors are nothing but a collection of a large number of transistors synthesized to perform a collective operation. But, the most basic oldest of the transistor is the BJT Transistor, hence in this article, we get into details of that, you can use the links to learn more about other power switches. BJT is the short form of Bipolar Junction Transistor , it is a solid-state current-controlled device which can be used to electronically switch a circuit, you can think of it as your normal Fan or Light switch, but instead of you turning it on manually it can be controlled electronically.
Technically speaking, BJT is a three-terminal device with an Emitter, collector, and a base pin, the current flow through the emitter and collector are controlled by the amount of current applied to the base. Again you can think of emitter and collector as the two ends of your switch and instead of pressing the switch, we have the base pin which can receive the control signal.
But how exactly does it work? And how to use a transistor to build interesting circuits? That's exactly what we are going to answer in this Tutorial.
Let's start with the symbol of transistors so that you can identify them in a circuit. The below diagram shows the symbols of the two types of transistors. As I said, you will be able to see the three terminals Emitter, Collector, and Base for both the type of Transistor. The difference between the PNP and NPN transistors is that the arrow mark at the emitter end if you have noticed, the arrow in the PNP transistor is mentioned as moving from the emitter to the base whereas in the NPN transistor the arrow will be moving from the base to the emitter.
The Direction of the arrow represents the direction of current flow in the transistor, in PNP the current will be flowing from emitter to base, similarly in the NPN transistor current will be flowing from the base to emitter. Another important difference is that an NPN transistor remains open until it receives a signal on the base pin while a PNP transistor remains closed until a control signal is provided to the base pin as shown in the above GIF file.
The BJT is formed by three layers of semiconductor materials, if it is a PNP transistor, it will have two P-type regions and one N-type region, likewise, if it is an NPN transistor, it will have two N-type regions and one P-type region.
The two outer layers are where the collector and emitter terminals are fixed and the base terminal is fixed at the center layer. The construction can simply be explained with a two diode analogy for transistor as shown in the above image, if you want to learn more about diodes , you can consider reading his article.
Consider the two diodes connected with each other using the cathode, then the meeting point can be extended to form the base terminal and the two anodes end acts as the collector and emitter of a PNP transistor.
Similarly, if you connect the anode ends of the Diode then the meeting point of the anodes can be extended to for the base terminal and the two cathode ends act as the collector and emitter of the NPN transistor. Practically the working of a transistor is very simple, it can be used as a switch or as an amplifier.
But for basic understanding lets start with how transistor as a switch works in a circuit. When a control voltage is provided to the base pin, the required base current I B flows into the base pin which is controlled by a base resistor. This current turns on the transistor switch is closed and allows the current to flow from collector to emitter. This current is called the collector current I C and the voltage across the collector and emitter is called V BE.
As you can see in the image, we are using a low-level voltage like 5V to drive a higher voltage load of 12V using this transistor. The width of the depletion region at the Junction CB is higher when compared with the depletion region of the Junction BE.
When the BE junction is forward biased it decreases the barrier potential, hence the electrons start flowing from the emitter to the base. The base region is very thin and it is lightly doped when compared with other regions, hence it consists of a very small number of holes, the electrons that are flowing from the emitter will recombine with the holes present in the base region and start to flow out of the base region in the form of the base current.
A large number of electrons that are left will move across the reverse bias collector junction in the form of the collector current.
Similarly, when you consider the PNP Transistor, they operate in the same way as the NPN transistor, but in NPN transistors the majority charge carriers are holes Positively charged particle but in the NPN transistor the charge carriers are the electrons negatively charged particle.
BJT can be connected in three different configurations by keeping one terminal common and using the other two terminals for the input and output. These three types of configurations respond differently to the input signal applied to the circuit because of the static characteristics of the BJT. The three different configurations of BJT are listed below. Among these, the Common Base configurations will have voltage gain, but no current gain, whereas the Common Collector Configuration has current gain, but no voltage gain and the Common Emitter Configuration will have both current and voltage gain.
The Common Base configuration is also called as the grounded base configuration , where the base of the BJT is connected as a common between both the input and output signal. The input current I E flowing through the emitter will be quite higher when compared with both the Base current I B and the Collector Current I C as the emitter current is the sum of both the Base current and Collector current.
Since the collector current output is less than the Emitter current input the current gain of this configuration will be unity 1 or less. Input characteristics. The input Characteristic curve for the Common Base configurations is drawn between the emitter current I E and the voltage between the base and emitter V EB. During the Common base configuration, the Transistor gets forward biased hence it will show characteristics similar to that of the forward characteristics of a p-n diode where the I E increases for fixed V EB when V CB increases.
Output Characteristics. The output characteristics of the Common Base configuration are given between the collector current I C and the voltage between the collector and base V CB , here the emitter Current I E is the measuring parameter. Based on the operation, there are three different regions in the curve, at first, the active region , here the BJT will be operating normally and the emitter junction is reverse biased. Next comes the saturation region where both the emitter and collector junctions are forward biased.
Finally, the cutoff region where both emitter and the collector junctions are reverse biased. The Common Emitter Configuration is also called the grounded emitter configuration where the emitter acts as the common terminal between the input applied between the base and emitter and the output obtained between the collector and the emitter. This configuration produces the highest current and power gain when compared with the other two types of configurations, this is because of the fact that the input impedance is low as it is connected to a forward-biased PN junction whereas the output impedance is high as it is obtained for the reverse-biased PN junction.
Input Characteristics. The input characteristics of the Common Emitter configuration are drawn between the base current I B and the voltage between the base and emitter V BE. Here the Voltage between the Collector and the emitter is the most common parameter. If you could see there will not be much difference between the characteristic curve of the previous configuration except for the change in parameters.
The CE configuration also has the three different regions, in the active region the collector junction is reverse biased and the emitter junction is forward biased, in the cut-off region, the emitter junction is slightly reverse biased and the collector current is not completely cut off, and finally, in the saturation region , both the collector and the emitter junctions are forward biased. The Common Collector Configuration is also called the grounded Collector configuration where the collector terminal is kept as the common terminal between the input signal applied across the base and the emitter, and the output signal obtained across the collector and the emitter.
This configuration is commonly called as the Voltage follower or the emitter follower circuit. This configuration will be useful for impedance matching applications as it has very high input impedance, in the region of hundreds of thousands of ohms while having relatively low output impedance. BJT can be used in various kinds of applications such as logic circuits, amplification circuits, oscillation circuits, multi-vibrator circuits, clipping circuits, circuits of the timer, time delay circuits, switching circuits, etc.
You can also check our different types of IC package articles to know the popular types and their names. Subscribe to stay updated with industry's latest Electronics components and news. The STM32Cube with graphical software configuration tool reduces development efforts, time, and cost. Bipolar Junction Transistor. Symbol of BJT Transistors Let's start with the symbol of transistors so that you can identify them in a circuit.
Working of Transistor BJT Practically the working of a transistor is very simple, it can be used as a switch or as an amplifier. Characteristics of BJT BJT can be connected in three different configurations by keeping one terminal common and using the other two terminals for the input and output.
Common Base CB Configuration The Common Base configuration is also called as the grounded base configuration , where the base of the BJT is connected as a common between both the input and output signal. Common Emitter CE Configuration The Common Emitter Configuration is also called the grounded emitter configuration where the emitter acts as the common terminal between the input applied between the base and emitter and the output obtained between the collector and the emitter.
Input Characteristics The input characteristics of the Common Emitter configuration are drawn between the base current I B and the voltage between the base and emitter V BE. Common Collector CC Configuration The Common Collector Configuration is also called the grounded Collector configuration where the collector terminal is kept as the common terminal between the input signal applied across the base and the emitter, and the output signal obtained across the collector and the emitter.
Application of Bipolar Junction Transistors BJT BJT can be used in various kinds of applications such as logic circuits, amplification circuits, oscillation circuits, multi-vibrator circuits, clipping circuits, circuits of the timer, time delay circuits, switching circuits, etc.
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Both p-n- p and the n- p-n transistors are the basic transistors which come under the category of bipolar junction transistors. These are used in the various amplifications circuits and the modulating circuits. NPN and PNP transistors are bipolar junction transistors, and it is a basic electrical and electronic component which is used to build many electrical and electronic projects. The operation of these transistors involves both electrons and holes. In PNP transistors, majority charge carriers are holes, whereas in NPN transistors, electrons are the majority charge carriers. The formation of these transistors is based on the diodes with the junction p-n.
Thus, we can say that the emitter current is the sum of the collector or the base current. Related terms: Difference Between NPN & PNP Transistor · Difference.
Working of NPN Transistor
Definition: The transistor in which one p-type material is placed between two n-type materials is known as NPN transistor. In NPN transistor, the direction of movement of an electron is from the emitter to collector region due to which the current constitutes in the transistor. Such type of transistor is mostly used in the circuit because their majority charge carriers are electrons which have high mobility as compared to holes. The NPN transistor has two diodes connected back to back. The diode on the left side is called an emitter-base diode, and the diodes on the left side are called collector-base diode.
Differences between NPN & PNP Transistors and their Making
The emitter-base junction of a transistor is forward biased whereas collector-base junction is reverse biased. However, if the emitter-base junction is also present, then forward bias on it causes the emitter current to flow. It is seen that this emitter current almost entirely flows in the collector circuit. Therefore, the current in the collector circuit depends upon the emitter current.
Earlier we have covered its basics in the previous post of transistors where I have explained about what it is and its types. A Transistor is a three layer semiconductor device in which one type of semiconductor Either P-type or N-type is sandwiched between two similar other types of semiconductor. In this type of transistor, n-type semiconductor piece is sandwiched between two pieces of p-type semiconductor layers. The basic block diagram of PNP transistor is shown in the image below:. As the Name suggests, in this type of transistor, p-type semiconductor piece is sandwiched between two pieces of n-type semiconductor layers. Look for the image below for its basic block diagram.
Working of a PNP transistor. At each junction, there is a depletion region which gives rise to a potential barrier. Since the emitter-base junction is forward biased, a large number of holes cross the junction and enters the base. At the same time, very few electrons flow from the base to the emitter. These electrons, when they reach emitter, recombine with an equal number of holes in the emitter. The loss of total number of holes in the emitter is made by flow of an equal number of electrons from the emitter to the positive terminal of the battery. The flow of holes from the emitter to base gives rise to emitter current I E.
This is in contrast to the npn transistor where the majority current carriers are electrons. To support this different type of current (hole flow), the bias batteries are.
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