PRINCIPLES OF. ELECTRONICS. (For B.E/ bestthing.info & other Engg. Examinations). NMM. S FREE CDZ. V.K. MEHTA. ROHIT MEHTA. Z containing S e-Book. and apply the IS principles upon which the Law of Success is based. the foundation of Napoleon Hill's philosophy of pe Load more similar PDF files. pdf book: Problems and Solutions on Solid State Physics, Relativity and Miscellaneous Topics by LIM CLICK HERE TO DOWNLOAD pdf book.
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Download Principles of Electronics By V. K. Mehta, Rohit Mehta – Electronics is a fascinating world of electrical circuits that involve active electrical components. [VK Mehta] Principles of Electronics - Ebook download as PDF File .pdf), Text File .txt) or read book online. Book for Principles of Electronics Engineering by VK. Albert P. Malvino was an electronics technician while serving in the U.S. Navy from to He graduated from the University of Santa Clara Summa Cum .
A gas-filled tube has. The noise in a gas-filled tube is Ionisation of cold cathode diode takes place at.. To stop conduction in a thyratron.. A cold cathode tube is generally used as a. A cold cathode diode is used as.
The gas-filled tubes can handle. The anode-to-cathode potential of a gasfilled tube at which gas deionises and stops conduction is called The cathode heating time of thermionic gas diode is. Conduction in a cold cathode tube is started by The internal resistance of a gas-filled tube is. How does current conduction take place in such a tube? Discuss some applications of glow tubes.
Explain how ionisation takes place in a hot-gas diode. Explain the differences between a gas tube and equivalent vacuum tube. Explain the construction. What is a thyratron? How does it differ from a vacuum triode? Give the schematic symbols of glow tube. What are the advantages of gas tubes over vacuum tubes? What is the difference between the action of thyratron and vacuum triode?
Why cannot thyratrons be used as rectifiers for high voltages? Can gas diodes be used as rectifiers for high voltages? What is the drawback of a gas diode compared to a thyratron? After this. Neils Bohr. Various scientists have given different theories regarding the structure of atom.
Danish Physicist gave clear explanation of atomic structure. According to Bohr: The method consists of studying the properties of atom experimentally. As it falls. The first orbit represents the first energy level. It has 14 electrons.
This state does not last long. The atom is said to be in a state of excitation. The electrons moving in a particular orbit possess the energy of that orbit. When this electron jumps from the second orbit to first.
Each orbit has fixed amount of energy associated with it. The larger the orbit. It becomes clear that outer orbit electrons possess more energy than the inner orbit electrons. The first. If an electron in the first orbit is to be lifted to the second orbit. A convenient way of representing the energy of different orbits is shown in Fig. Atomic Structure 49 ii The electrons can revolve around the nucleus only in certain permitted orbits i.
These electrons can revolve only in permitted orbits i. This is known as energy level diagram. The larger the orbit i. M orbits respectively. Neils Bohr Two electrons revolve in the first orbit. The range of energies possessed by an electron in a solid is known as energy band. Each orbit of an atom has a single energy. The larger the orbit of an electron. Since there are millions of first orbit electrons. The electrons in the first orbit can have any energy range in this band.
This is known as energy band. The result is that the electron in any orbit of such an atom can have a range of energies rather than a single energy. The electrons in the lower energy band are tightly bound to the nucleus and play no part in the conduction process. M etc. In fact. The width of the forbidden energy gap is a measure of the bondage of valence electrons to the atom. No electron of a solid can stay in a forbidden energy gap as there is no allowed energy state in this region.
The difference in the behaviour of solids as regards their electrical conductivity can be beautifully explained in terms of energy bands.
Principles of Electronics
The partially filled band can accommodate more electrons. The electrons in the outermost orbit of an atom are known as valence electrons. There is also an intermediate class of semiconductors. The separation between conduction band and valence band on the energy level diagram is known as forbidden energy gap. The range of energies i.
In certain materials e. Atomic Structure 51 4. This band may Fig. In terms of energy band. Even at ordinary temperature. All electrons in the conduction band are free electrons. In a normal atom. If a substance has empty conduction band. In order to push an electron from valence band to the conduction band i. Insulators e. The greater the energy gap. Though there are a number of energy bands in solids. On the other hand. In short. Conductors e. This shows that electrical conductivity of a semiconductor increases with the rise in temperature i.
At low temperature. As the temperature is increased. Semiconductors e. It is because there are a large number of free electrons available in a conductor. Due to this overlapping. Atomic Structure 53 4. Silicon atom i Fig. For an electron to jump from one orbit to the next higher orbit. The valence electrons in germanium are in the fourth orbit while the valence electrons in silicon are in the third orbit. As the electronic field advanced.
No electron can exist in the energy gap. This is the basic reason why silicon is widely used as semiconductor material. This means that germanium valence electrons require smaller amount of additional energy to escape from the atom and become free electron. Since silicon is the most widely used material in the manufacture of semiconductor devices. What is the effect of this property? This property makes germanium more unstable at high temperatures. There are 4 valence electrons in the outer valence shell.
The atomic number of silicon is 14 so that its 14 electrons are distributed in 3 orbits. The conduction band is shown to have an energy level of 1. Describe the valence band.. When an electron jumps from higher orbit to a lower orbit.
The energy gap between valence and conduction bands in insulators is about.
In a conductor Explain the concept of energy bands in solids As you will see.. In a semiconductor. Give the energy band description of conductors A semiconductor has. In insulators.. Discussion Questions 1. Why is the energy of an electron more in higher orbits? What is the concept of energy band? Why do conduction band electrons possess very high energy? Why are valence electrons of a material so important?
What is the difference between energy level and energy band? The electrons in the conduction band are known as.. Thus for an electron to jump from the valence band to the conduction band The electrons in the third orbit of an atom have.. Such substances are classified as semiconductors. Semiconductor Physics 5. Voltage across pnJunction or Biasing a pn. Semiconductors have some useful properties and are being extensively used in electronic circuits.
Transistors are only one of the family of semiconductor devices. This bonding is due to the fact that it is the tendency of each atom to complete its last orbit by acquiring 8 electrons in it. This shows that resistivity of a semiconductor lies inbetween conductors and insulators. Properties of Semiconductors i The resistivity of a semiconductor is less than an insulator but more than a conductor. Such bonds are called co-valent bonds. This property is most important and is discussed later in detail.
This gave such substances like germanium the name of semiconductors. This makes the atom active to enter into bargain with other atoms to acquire 8 electrons in the last orbit. This shows that electrically germanium cannot be regarded as a conductor or insulator or a resistance material.
It is interesting to note that it is not the resistivity alone that decides whether a substance is semiconductor or not.
The reader may wonder. In semiconductors. The answer shall be readily available if we study the following table: In the formation of a co-valent bond. To do so. The following points may be noted regarding the co-valent bonds: In this business of sharing. In this way. All semi-conductors have crystalline structure.
It is the tendency of each germanium atom to have 8 electrons in the last orbit. The two most frequently used materials are germanium Ge and silicon Si. Semiconductor Physics 57 Fig. Each neighbouring atom shares one valence electron with the central atom.
It is because the energy required to break their co-valent bonds i. First orbit has 2 electrons. Two electrons are in the first orbit. Germanium has become the model substance among the semiconductors. It is recovered from the ash of certain coals or from the flue dust of zinc smelters. Germanium is an earth element and was discovered in It is clear that germanium atom has four valence electrons i.
Mehta V.K., Mehta R. Principles of Electronics
It is clear that silicon atom has four valence electrons i. Like germanium.
As the atoms are arranged in an orderly pattern. Silicon is an element in most of the common rocks. In terms of energy band description. At absolute zero temperature. It is due to the non-availability of free electrons that a semiconductor behaves as an insulator.
Semiconductor Physics 59 5.
This is a very important point to keep in mind. At this temperature. Even at room temperature. It may be seen that forbidden energy gap is very small. The inner orbit electrons are bound whereas the valence electrons are engaged in co-valent bonding. The energy band description is extremely helpful in understanding the current flow through a semiconductor.
It may be added that at room temperature. When the temperature is raised. The breaking of bonds sets those electrons free which are engaged in the formation of these bonds. The result is that a few free electrons exist in the semiconductor. These free electrons can constitute a tiny electric current if potential difference is Fig.
At the. It may be noted that each time a valence electron enters into the conduction band. This shows that the resistance of a semiconductor decreases with the rise in temperature i.
As the temperature is raised. As we shall see in the next article. Thus the hole having a positive charge has moved from L to N i. Now the valence electron at M comes to fill the hole at L. Another valence electron say at N in turn may leave its bond to fill the hole at M. A valence electron say at M from nearby co-valent bond comes to fill in the hole at L. The result is that hole disappears at L and appears at M. This constitutes hole current.
The hole current can be beautifully explained in terms of energy bands.
The ONE Thing: The Surprisingly Simple Truth Behind Extraordinary Results
Suppose the valence electron at L See Fig. Suppose due to thermal energy. This results in the creation of hole at M. This creates a hole in the co-valent bond at L. The current conduction by holes can be explained as follows: The hole shows a missing electron. Semiconductor Physics 61 same time. When a covalent bond is broken due to thermal energy. It is clear that valence electrons move along the path PNML whereas holes move in the opposite direction i.
The reader may wonder why to call it a hole current when the conduction is again by electrons of course valence electrons! The answer is that the basic reason for current flow is the presence of holes in the co-valent bonds. This leaves a vacancy at L. For one electron set free. The amount and type of such impurities have to be closely 8 controlled during the preparation of extrinsic semiconductor. The free electrons are produced due to the breaking up of some covalent bonds by thermal energy.
As the holes reach the negative terminal B. In an intrinsic semiconductor. This is achieved by adding a small amount of suitable impurity to a semiconductor. The purpose of adding impurity is to increase either the number of free electrons or holes in the semiconductor crystal.
It is then called impurity or extrinsic semiconductor. Depending upon the type of impurity added. This creates new holes near the positive terminal which again drift towards the negative terminal.
[VK Mehta] Principles of Electronics
To be useful in electronic devices. When electric field is applied across an intrinsic semiconductor. It may be noted that current in the external wires is fully electronic i. The process of adding impurities to a semiconductor is known as doping. As we shall see. What about the holes? The current conduction in an n-type semiconductor is predominantly by free electrons i. The four valence electrons of pentavalent atom form covalent bonds with four neighbouring germanium atoms.
Semiconductor Physics The addition of pentavalent impurity provides a large number of free electrons in the semiconductor crystal. As the current flow through the crystal is by free electrons which are carriers of negative charge. Typical examples of pentavalent impurities are arsenic At. When p. Arsenic is pentavalent i. The following points may be noted carefully: We know that germanium atom has four Fig.
It is due to this predominance of electrons over holes that it is called n-type semiconductor n stands for negative.. Though each arsenic atom provides one free electron. When a small amount of pentavalent impurity like arsenic is added to germanium crystal. The reason is simple. To understand n-type conductivity. The fifth valence electron of arsenic atom finds no place in co-valent bonds and is thus free as shown in Fig.
An arsenic atom fits in the germanium crystal in such a way that its four valence electrons form covalent bonds with four germanium atoms. The addition of pentavalent impurity has produced a number of conduction band electrons i. Such impurities which produce n-type semiconductor are known as donor impurities because they donate or provide free electrons to the semiconductor crystal.
It may be noted that conduction is just as in ordinary metals like copper. The fifth left over valence electron of the pentavalent atom cannot be accommodated in the valence band and travels to the conduction band.
It is due to the predominance of holes over free electrons that it is called p-type semiconductor p stands for positive. Each atom of gallium fits into the germanium crystal but now only three co-valent bonds can be formed. Such impurities which produce p-type semiconductor are known as acceptor impurities because the holes created can accept the electrons. Gallium is trivalent i. A small amount of gallium provides millions of holes.
Typical examples of trivalent impurities are gallium At. The addition of trivalent impurity has produced a large number of holes. To explain the formation of p-type semiconductor. When a small amount of trivalent impurity like gallium is added to germanium crystal. In the fourth co-valent bond. The addition of trivalent impurity provides a large number of holes in the semiconductor. But the holes far outnumber the conduction band electrons.
This missing electron is called a hole. It is because three valence electrons of gallium atom can form only three single co-valent bonds with three germanium atoms as shown in Fig. An n-type material has its share of electron-hole pairs released due to breaking of bonds at room temperature but in addition has a much larger quantity of free electrons due to the effect of impurity. It follows. The current conduction in p-type semiconductor is predominantly by holes i.
But this conclusion is wrong. The situation with regard to p-type semiconductor is also similar. The extra electrons are free electrons and increase the conductivity of the semiconductor. Semiconductor Physics 65 Fig. The reader may think that n-type material has a net negative charge and p-type a net positive charge. It may be noted that in p-type conductivity. To understand p-type conductivity. It is true that n-type semiconductor has excess of electrons but these extra electrons were supplied by the atoms of donor impurity and each atom of donor impurity is electrically neutral.
When the impurity atom is added. The free electrons in this case are considered majority carriers — since the majority portion of current in n-type material is by the flow of free electrons — and the holes are the minority carriers. These impurity-caused free electrons are not associated with holes. As the holes are positively charged. Formation of pn junction.
This button serves as a suitable base for soldering on leads. In actual practice. Under proper conditions. A thorough knowledge of the formation and properties of pn junction can enable the reader to understand the semiconductor devices.
The temperature is then lowered and puddle begins to solidify. When all germanium has been redeposited. As the process goes on.
One common method of making pn junction is called alloying. The pn junction is of great importance because it is in effect.
Most semiconductor devices contain one or more pn junctions. The addition of indium overcomes the excess of electrons in the n-type germanium to such an extent that it creates a p-type region. The indium and some of the germanium melt to form a small puddle of molten germanium-indium mixture as shown in Fig. This is shown by a black arrow in Fig. The positive and negative charges set up an electric field. Semiconductor Physics 67 5.
This creates a layer of positive charges pentavalent ions near the junction.
The result is that there is a layer of negative charges trivalent ions near the junction. For germanium. It may be noted that depletion layer is formed very quickly and is very thin compared to the n region and the p region. The term depletion is due to the fact that near the junction. These two layers of positive and negative charges form the depletion region or depletion layer.
The typical barrier potential is approximately: For silicon. For clarity. The result is that n region loses free electrons as they diffuse into the junction. The electric field is a barrier to the free electrons in the n-region.
There exists a potential difference across the depletion layer and is called barrier potential V0. The barrier potential of a pn junction depends upon several factors including the type of semiconductor material. As the electrons move across the junction. In relation to a pn junction. Reverse biasing 1. The increased potential barrier prevents the flow of charge carriers across the junction.
To apply reverse bias. As potential barrier voltage is very small 0. Once the potential barrier is eliminated by the forward voltage. To apply forward bias. Forward biasing.
It is clear that applied reverse voltage establishes an electric field which acts in the same direction as the field due to potential barrier. Forward biasing 2. This is called forward current. Reverse biasing. When external d. The magnitude of current depends upon the applied forward voltage. When the external d. Rf to current flow. With reverse bias to pn junction. With forward bias to pn junction.
The applied forward potential establishes an electric field which acts against the field due to potential barrier. When the valence electrons reach the left end of the crystal. From the above discussion.
Principles of Electronics
Under the influence of forward voltage. The valence electrons move towards left in the p-region which is equivalent to the holes moving to right. As valence electrons.
Rr to current flow. Semiconductor Physics ii The junction offers very high resistance called reverse resistance. As the free electrons reach the junction. It repels the free electrons in n-type towards the junction.
When a free electron combines with a hole. When the external voltage is zero. The characteristics can be studied under three heads. It prevents the forward current from exceeding the permitted value.
The forward current through a pn junction is due to the majority carriers produced by the impurity. The curve is almost linear. It may be recalled that there are a few free electrons in p-type material and a few holes in n-type material.
At this stage breakdown of the junction occurs. With reverse bias to the pn junction i. From the forward characteristic.
If reverse voltage is increased continuously. It is the minimum reverse voltage at which pn junction breaks down with sudden rise in reverse current. Diodes and Transistors The diode, a circuit element, encourages current to flow in only one direction.
It has two terminals, unlike the transistor—which has three. In the transistor, current can flow in more than one direction. Both diodes and transistors modulate current direction and voltage. Inductors, Transformers and RLC Circuit Basic electronics circuits often include inductors and transformers as circuit elements.
An inductor is a coil of wire that produces a desired magnetic field, unlike a capacitor, which produces a desired electric field. Transformers, another type of circuit element, can step up a voltage or step it down to desired values.
All these circuit components make up what is generally called "basic electronics. These include analog and digital meters that measure voltages, current, resistance and capacitance; power supplies, which provide stable regulated voltage and current; oscilloscopes, which measure circuit waveforms from circuits; and function generators, which provide standard desired waveforms.
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Trending on EasyEngineering. November Karve, Dr March August July 9. Ritz Book Free June 9.When potential difference is applied across a conductor, the free electrons move towards the positive terminal of supply, constituting electric current. The electrons in the conduction band are known as.. Thus for an electron to jump from the valence band to the conduction band Introduction 17 Fig.
Meissner Oscillators Depending upon the type of impurity added. The equivalent circuit of an a.
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