Bjt and fet transistor pdf

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bjt and fet transistor pdf

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It is so because the operation of BJT is dependent on injection and collection of minority charge carriers that includes both electrons and holes. As against JFET is majority carrier device, thus termed as unipolar. We will discuss some other major differences between BJT and JFET but before proceeding further have a look at the contents to be discussed under this article. BJT is the short form used for bipolar junction transistor. It is a 3 terminal device that is used for switching or amplification purpose.

What’s the difference between MOSFET and BJT?

It is so because the operation of BJT is dependent on injection and collection of minority charge carriers that includes both electrons and holes. As against JFET is majority carrier device, thus termed as unipolar. We will discuss some other major differences between BJT and JFET but before proceeding further have a look at the contents to be discussed under this article. BJT is the short form used for bipolar junction transistor. It is a 3 terminal device that is used for switching or amplification purpose.

The figure below shows the basic construction of a bipolar transistor consisting of 3 terminals emitter, base and collector. It is formed by fusing two p-n junction diodes, that shares a common terminal.

The common terminal can be either p or n as we can see in the figure shown above. It is a current regulating device which controls the current flowing through it.

There exist two different configurations of a BJT, i. Both hold the same operating principle but the difference between the two is their biasing and polarity of power supply voltage. In normal operating conditions, EB junction is always forward biased whereas CB junction is always reverse biased as we can see in the figure shown above.

Due to the forward applied voltage V EB , the electrons in the N region experiences repulsive force and drifts across the lightly doped base region after overcoming the barrier potential. As the base region is lightly doped, only some of the drifted electrons recombine with the holes in the base region.

Now, the increased concentration of electrons in the base region causes more electrons to move across the collector region. As this region is reversed biased, the electrons are immediately collected by this region.

Thus, a proper flow of current is noticed and hence the emitter current is the summation of base and collector current. It is a 3 terminal unipolar device that controls the flow of current through the device by the applied input voltage. Here, the 3 terminals are termed as the source, gate and drain. It is known so because the output current of the device is controlled by the field associated with depletion region. As it is a voltage controlled device thus the applied input potential allows the movement of electrons hence causing current to flow through the device.

The figure below shows an n channel JFET with the positive voltage at the drain terminal. In the absence of any applied input voltage, the two depletion region around the PN junctions is equally wide and symmetrical. However, on applying a positive potential to the drain wrt source, electrons start flowing from source to drain.

Thus, causing the drain current to flow through the drain to source. Another condition exists when the gate terminal is applied with negative potential and drain is positively biased as we can see below:. This reverse biasing of the p-n junction allows a considerable increase in the width of the depletion region. Resultantly, this narrows the channel length and drain current is decreased due to an increase in resistance. Any additional increase in the gate voltage will cause the drain current to cut-off completely.

Conversely, by lowering the negative biasing of the gate terminal, the width of the depletion region reduces. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. On the contrary, JFET is a device whose output current is controlled by the input voltage applied to it. Leave a Reply Cancel reply Your email address will not be published.

Field-effect transistor

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. BJTs use two junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material. The junctions can be made in several different ways, such as changing the doping of the semiconductor material as it is grown, by depositing metal pellets to form alloy junctions, or by such methods as diffusion of n-type and p-type doping substances into the crystal. The superior predictability and performance of junction transistors soon displaced the original point-contact transistor. Diffused transistors, along with other components, are elements of integrated circuits for analog and digital functions.

Latest Articles in "Industry News". Source: Electronic Tutorials. The voltage that is applied across the gate controls how much current flows into the drain. Both of these types can either be in enhancement or depletion mode see figure 1. The gate terminal itself is made from metal and is detached from the source and drain terminals using a metal oxide.


The Field Effect Transistor (FET) is an active device. In simple terms, it is a voltage controlled valve. The gate-source voltage (VGS) controls the drain current (ID).


Classification and Different Types of Transistors | BJT, FET, NPN, PNP

The field-effect transistor FET is a type of transistor that uses an electric field to control the flow of current. FETs are devices with three terminals: source , gate , and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source. FETs are also known as unipolar transistors since they involve single-carrier-type operation. That is, FETs use either electrons or holes as charge carriers in their operation, but not both.

There are many types of transistors in use. Each transistor is specialized in its application. The main classification is as follows. Let us have a look at the BJTs.

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.

These types of devices allow a greater degree of control over their work. The major difference between BJT and FET is that in a field-effect transistor only majority charge carries flows, whereas in BJT both majority and minority charge carriers flow. The BJT is one type of transistor that uses both majority and minority charge carriers.

Chapter 1 " FIELD EFFECT TRANSISTOR "

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In this tutorial, we will learn about the classification and different Types of Transistors. The Transistor became an essential component in modern electronics and we cannot imagine the World without Transistors. Transistor is a semiconductor device which is used to amplify the signals as well as in switching circuits. Generally transistor is made of solid material which contains three terminals such as emitter E , Base B and Collector C for connections with other components in the circuit. Some transistors contains fourth terminal also i. Transistor is one of the active components. From the time of first transistor invention to present days the transistors are classified into different types depending on either construction or operation, they are explained using tree diagram as below.

Key Differences Between BJT and JFET

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Bipolar junction transistor

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