Muthayamma Engineering College Lecture Handouts - Electronic Devices PDF
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Muthayammal Engineering College
Dr. J.Rangarajan
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These lecture handouts are for ECE students at Muthayamma Engineering College. They cover the basics of semiconductor diodes, including drift and diffusion currents, as well as the theory of PN Junction diodes. The handouts include relevant definitions, equations, and diagrams.
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MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu...
MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-1 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Review of Semiconductor physics Introduction: Semiconductors are materials which have a conductivity between conductors (generally metals) and nonconductors or insulators (such as most ceramics). Semiconductors can be pure elements, such as silicon or germanium, or compounds such as gallium arsenide or cadmium selenide. Prerequisite knowledge for Complete understanding and learning of Topic: Atomic structure, Energy band diagram, conductor and insulator Detailed content of the Lecture: In an atom, electrons in the innermost orbits, which are filled, are called Valence electrons. On the other hand, electrons in the outer orbits that do not fill the shell completely are called Conduction electrons. The energy band which includes the energy levels of the valence electrons is called Valence band. Also, the energy band above it is called Conduction band. In case of metallic conductors, conduction band overlaps on the electrons in the valence band. In insulators, there is a large gap between both these bands. Hence, the electrons in the valence band remain bound and no free electrons are available in the conduction band. Semiconductors have a small gap between both these bands. Some valence electrons gain energy from external sources and cross the gap between the valence and conduction bands. Solids can be classified as metals, semiconductors or insulators based on conductivity or resistivity and energy bands in electronics. Semiconductors are materials which have a conductivity between conductors (generally metals) and nonconductors or insulators (such as most ceramics). Semiconductors can be pure elements, such as silicon or germanium, or compounds such as gallium arsenide or cadmium selenide. Semiconductors can be broadly classified into Intrinsic and Extrinsic Semiconductors. An Intrinsic Semiconductor is the purest form of a semiconductor, elemental, without any impurities. Extrinsic Semiconductors are semiconductors which conduct even at room temperature. This is achieved by adding impurities to the pure semiconductor. Doping is the process of adding impurities to intrinsic semiconductors to alter their properties. Crystals of Silicon and Germanium are doped using two types of dopants: Pentavalent (valency 5); like Arsenic (As), Antimony (Sb), Phosphorous (P), etc. Trivalent (valency 3); like Indium (In), Boron (B), Aluminium (Al), etc. An n-type semiconductor is created when pure semiconductors, like Si and Ge, are doped with pentavalent elements. A p-type semiconductor is created when trivalent elements are used to dope pure semiconductors, like Si and Ge. The P stands for Positive, which means the semiconductor is rich in holes or Positive charged ions. The N stands for Negative, which means the semiconductor is rich in electrons or Negative charged ions. Video Content / Details of website for further learning (if any): 1. http://community.wvu.edu/~dwgraham/classes/ee551/slides/semiconductor_overview.pdf 2. https://www.toppr.com/guides/physics/semiconductor-electronics-materials-device-and-simple- circuits/extrinsic-semiconductor/ 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, Jacob Millman, Christos Halkias, McGraw Hill, Third Edition, 2001. (1-7) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-2 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Drift and diffusion currents, Continuity Equation Introduction: Drift current and diffusion current are the two types of currents flowing through the PN junction. Diffusion current flows due to the movement of particles from the region of high concentration towards the region of low concentration. Drift current is the flow of current due to the application of external field. Prerequisite knowledge for Complete understanding and learning of Topic: Energy band diagram, PN junction, Barrier potential Detailed content of the Lecture: Drift Current Drift Current: The applied electric field will accelerate the carrier and produce a net movement of charges. This movement of charge carrier due to the applied electric field is called Drift current. P N Let P be the charge density and Vd be the drift velocity. Then, Drift volume current density due to holes is given by Jp (drift ) = PVdp Where, P = qp q = charge of electron = 1.602 × 10 -19 coulomb. p = Number of holes per cubic cm. Vdp = Average drift velocity of holes = µpE, where µp = mobility of hole Similarly, charge density due to electron is given by, Jn (drift) = q µnnE Therefore, Total drift current J (drift) = q (µnn + µpP) E Diffusion Current Diffusion is the process of flow of particles from the region of high concentration towards the region of low concentration. This movement of charge particles will results in the diffusion current. n(x) n (+l) n (0) n (-l) x = -l x = 0 x = +l x The above graph depicts the variation of electron concentration with respect to distance. Diffusion current due to electron and holes are given by, dn J n diffusion q Dn dx dp J p diffusion q Dp dx The total current density in the semiconductor is due to the sum of the drift and diffusion current density. dp For holes, J p q p PE q Dp dx dn For electron, J n q n nE q Dn dx Video Content / Details of website for further learning (if any): 1. http://www.sciencecampus.com/engineering/electronics/semiconductor_theory 2. https://www.tutorialspoint.com/electronic_circuits 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (84-86) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-3 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Theory of PN Junction Diode, Diode Current Equation Introduction: Diode is a semiconductor device that allows the current to pass through it in one direction and will not allow in other direction. It is formed by joining the P type and N type semiconductor together. The current that is flowing through the diode is governed by the diode current equation. knowledge for Complete understanding and learning of Topic: Atomic structure, Energy band diagram, P type and N type semiconductor Detailed content of the Lecture: PN junction Diode Diode is a semiconductor device that allows the current to pass through it in one direction and will not allow in other direction. The diode which is formed by doping one half by P type impurity and other half by N – type impurity is called PN junction diode. Structure of PN junction Diode Symbol P N A Anode Cathode C PN junction (or) metallurgical junction The interface that separate N and P region is referred to as the PN junction (or) metallurgical junction. Electron in the N region will try to move towards P region and holes in the P region will try to move towards N region, which result in the diffuse of electron on P – side and diffuse of holes on N – side. This process is called Diffusion. Thus, the movement of the mobile charge carriers to the junction due to the difference in the concentration resulting in a region called depletion region. The depletion region (or) space region (or) transition region which is formed near the junction will restricts the movement of electrons and holes towards P region and N region An electrostatic potential difference is created near the metallurgical junction which is known as potential barrier, junction barrier, diffusion potential (or) contact potential (VB). This is due of the diffused oppositely charged ions present on both sides of PN junction. Depletion region is of 0.5 µm thickness and the magnitude of contact potential, potential barrier , junction barrier (or) diffusion potential Vo is of 0.3 v for Ge and 0.7 v for Si. PN junction diode and formation of depletion region P N Holes (+) Electrons (-) Depletion region Potential barrier Voltage V Heigh (v0) t Width Distance Forward biasing: If the positive terminal of the voltage source is connected to the P type side and negative terminal of the voltage source is connected to the N type of the junction diode. Then the biasing is known as forward biasing. Reverse biasing: If the positive terminal of the voltage source is connected to the N side and negative terminal of the voltage source is connected to the P – side of the junction diode. Then the biasing is known as Reverse Biasing. Peak inverse voltage: It is the maximum reverse voltage that can be applied to the PN junction without damage to the junction. Diode current equation The diode current equation relating the voltage V and current I is given by I = I0 * [exp (qV / n*k*T) –1] Where, I – diode current I0 – diode reverse saturation current at room temperature q – charge of electron (1.6x10^-19 C) V – external voltage applied to the diode K – Boltzmann’s constant (1.38066x10^-23 J/K) T – temperature of the diode junction n - n is a junction constant (typically around 2 for diodes, 1 for transistors) Video Content / Details of website for further learning (if any): 1. https://www.tutorialspoint.com/electronic_circuits 2. https://www.electronicshub.org/characteristics-and-working-of-p-n-junction-diode 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (84-98) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-4 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Current Voltage Characteristics Introduction: The current-voltage or VI characteristic of a PN diode is the graphical representation of how the diode behalves in the forward and reverse bias condition. Prerequisite knowledge for Complete understanding and learning of Topic: PN Diode, Depletion Region, Biasing Detailed content of the Lecture: Applying external voltage of proper magnitude is known as Biasing. (i) Forward Bias If the positive terminal of the voltage source is connected to the P type side and negative terminal of the voltage source is connected to the N type side of the junction diode. Then the biasing is known as forward biasing. Positive potential which is applied to the P type side repels the holes towards the junction. Negative potential which is applied to the N type side repels the electrons towards the junction. Current (mA) Depletion Region (v) (mA) P region N Ge Si W Holes flow Electron flow VP Voltage 0.3v 0.7v (v) Characteristics of forward bias When the applied potential (VP) is less than Potential Barrier (VB), the potential barrier prevents the holes and electrons to move on opposite side. Hence there will be no increases in current till threshold voltage. When the applied potential (VP) is greater than Potential Barrier (VB), the potential barrier disappears completely makes the electron to move towards positive terminal and holes towards negative potential results in large current flow. (ii) Reverse Bias If the positive terminal of the voltage source is connected to the N type side and negative terminal of the voltage source is connected to the P type side of the junction diode. Then the biasing is known as Reverse Biasing. Increased Forward current (mA) P depletion region N Breakdown voltage Reverse Forward voltage voltage W (v) (v) Holes Electron s Breakdown Characteristics of reverse bias Reverse current (A) Negative potential which is applied to the P- type side attract the holes towards the negative terminal. Positive potential which is applied to the N type side attract the electrons towards the positive terminal. This results in the increases in the depletion region When the Reverse bias is increased. The depletion region increases. Therefore this offers high resistivity in the region. Theoretically there is no current flow, but practically a small microampere current flows due to minority carrier this is known as reverse saturation currents. The minority carrier obtains enough kinetic energy to break the junction and hence a large reverse current flows after the particular Voltage. This is due to the breakdown at the junction and this voltage is known as Breakdown Voltage. Video Content / Details of website for further learning (if any): 1. https://www.tutorialspoint.com/electronic_circuits 2. https://www.electronicshub.org/characteristics-and-working-of-p-n-junction-diode 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, Jacob Millman, Christos Halkias, McGraw Hill, Third Edition, 2001, (124-126) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-5 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Effect of Temperature on PN Junction diodes Introduction: PN junction diode parameters like reverse saturation current, bias current, reverse breakdown voltage and barrier voltage are dependent on temperature. With the increase in temperature, the intrinsic carrier concentration increases. Therefore, the barrier potential is decreased and in turn the current conduction starts at earlier stage. Prerequisite knowledge for Complete understanding and learning of Topic: PN diode, Barrier potential, Diode Characteristic Detailed content of the Lecture: Forward Bias With the increase in temperature, the intrinsic carrier concentration increases. This pushes the fermi level closer to the intrinsic fermi level (the middle of the band gap). The fermi level in each region moves closer to the middle of the gap, and the built-on potential is decreased. Reverse Bias Intrinsic concentration would increase with increase in temperature and hence minority charges also increase with increase in temperature. The reverse current depends on minority carriers. Hence as the number of minority charge carriers increase, the reverse current would also increase with temperature PN junction diode parameters like reverse saturation current, bias current, reverse breakdown voltage and barrier voltage are dependent on temperature. Mathematically diode current is given by I = I0 * [exp (qV / n*k*T) –1] Where, I – diode current I0 – diode reverse saturation current at room temperature q – charge of electron (1.6x10^-19 C) V – external voltage applied to the diode K – Boltzmann’s constant (1.38066x10^-23 J/K) T – temperature of the diode junction n - n is a junction constant (typically around 2 for diodes, 1 for transistors) Hence, the current should decrease with increase in temperature but exactly opposite occurs. There are two reasons: Rise in temperature generates more electron-hole pair thus conductivity increases and thus increase in current Increase in reverse saturation current with temperature offsets the effect of rise in temperature Reverse saturation current (IS) of diode increases with increase in the temperature. The rise is 7ºC for both germanium and silicon and approximately doubles for every 10ºC rise in temperature. Thus if we kept the voltage constant, as we increase temperature the current increases. Barrier voltage is also dependent on temperature and it decreases by 2mV/ºC for germanium and silicon. Reverse breakdown voltage (VR) also increases with the increase in temperature. Video Content / Details of website for further learning (if any): 1. https://www.electronicshub.org/characteristics-and-working-of-p-n-junction-diode/ 2. https://www.tutorialspoint.com/electronic_circuits/electronic_positive_clipper_circuits.htm 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (111-112) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-6 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Diffusion Capacitance, Applications of diode Introduction: Diffusion capacitance occurs in a forward biased p-n junction diode. Diffusion capacitance is also referred as storage capacitance. The diffusion capacitance occurs due to stored charge of minority electrons and minority holes near the depletion region. In a forward biased diode, diffusion capacitance is much larger than the transition capacitance. Prerequisite knowledge for Complete understanding and learning of Topic: Energy band diagram, Barrier region, PN diode, Biasing Detailed content of the Lecture: In a p-n junction diode, two types of capacitance take place. They are, Transition capacitance (CT) Diffusion capacitance (CD) Transition capacitance (CT) The amount of capacitance changed with increase in voltage is called transition capacitance. The transition capacitance is also known as depletion region capacitance, junction capacitance or barrier capacitance. Transition capacitance is denoted as CT. Just like the capacitors, a reverse biased p-n junction diode also stores electric charge at the depletion region. The depletion region is made of immobile positive and negative ions. In a reverse biased p-n junction diode, the p-type and n-type regions have low resistance. Hence, p-type and n-type regions act like the electrodes or conducting plates of the capacitor. The depletion region of the p-n junction diode has high resistance. Hence, the depletion region acts like the dielectric or insulating material. Thus, p-n junction diode can be considered as a parallel plate capacitor. Diffusion capacitance (CD) Diffusion Capacitance is the capacitance due to transport of charge carriers between two terminals of a device, for example, the diffusion of carriers from anode to cathode in forward bias mode of a diode In the forward biased diode, the potential barrier at the junction gets lowered. As a result, holes get injected from the P-side to the N-side and electron get injected from the N-side to the P-side. These injected charges get stored near the junction just outside the depletion layer, holes in the N-region and electrons in the P-region. Due to charge storage, the voltage lags behind the current producing the capacitance effect. Such a capacitance is called diffusion capacitance or storage capacitance [CD]. In a general case, diffusion constant CD is caused by diffusion of both the holes in the n-regions and electrons in the P-region The diffusion capacitance CD may be defined as the rate of change of injected charge with voltage. CD = dQ / dV Where, CD = Diffusion capacitance dQ = Change in number of minority carriers stored outside the depletion region dV = Change in voltage applied across diode Diffusion capacitance is always smaller than transition capacitance, both are few tens of pico farads. In a forward biased diode, the transition capacitance exist. However, the transition capacitance is very small compared to the diffusion capacitance. Hence, transition capacitance is neglected in forward biased diode. PN Junction diode application: 1. Switching element in logical circuit. 2. In power supplies, it is used as rectifier and voltage regulator. 3. LED and LASER, a form PN junction diode is commonly used in optical communication. 4. It is used as an oscillator in microwave circuit and tuning element in receiver circuit. Video Content / Details of website for further learning (if any): 1. https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits/semiconductor- diodes/junctioncapacitance-transitioncapacitance-diffusioncapacitance.html 2. https://bestengineeringprojects.com/transition-capacitance-and-diffusion-capacitance-of-diode/ 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (109-110) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu LECTURE HANDOUTS L – 7A ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Rectifiers Introduction: An alternating current has the property to change its state continuously. But during the process of rectification, this alternating current is changed into direct current DC. The wave which flows in both positive and negative direction then will get its direction restricted only to positive direction, when converted to DC. Prerequisite knowledge for Complete understanding and learning of Topic: PN Diode, Biasing, Transformer Detailed content of the Lecture: Rectifier Rectifier is a circuit which converts an alternating current into a direct current. There are two main types of rectifier circuits, depending upon their output. They are Half-wave Rectifier and Full-wave Rectifier A Half-wave rectifier circuit rectifies only positive half cycles of the input supply whereas a Full-wave rectifier circuit rectifies both positive and negative half cycles of the input supply. Half-wave Rectifier The name half-wave rectifier itself states that the rectification is done only for half of the cycle. The AC signal is given through an input transformer which steps up or down according to the usage. Mostly a step down transformer is used in rectifier circuits, so as to reduce the input voltage. Input Waveform Rectifier Circuit Output Waveform The input signal is given to the transformer which reduces the voltage levels. The output from the transformer is given to the diode which acts as a rectifier. This diode gets ON and conducts for positive half cycles of input signal. Hence a current flows in the circuit and there will be a voltage drop across the load resistor. The diode gets OFF and does not conduct for negative half cycles. Hence, the output for negative half cycles will be, iD = 0 and Vo = 0. Full-Wave Rectifier A Rectifier circuit that rectifies both the positive and negative half cycles can be termed as a full wave rectifier as it rectifies the complete cycle. The construction of a full wave rectifier can be made in two types. They are (i) Center-tapped Full wave rectifier (ii) Bridge full wave rectifier (i) Center-tapped full wave rectifier A rectifier circuit whose transformer secondary is tapped to get the desired output voltage, using two diodes alternatively, to rectify the complete cycle is called as a Center-tapped Full wave rectifier circuit. Rectifier Circuit Input Waveform When the positive half cycle of the input voltage is applied, the point M at the transformer secondary becomes positive with respect to the point N. This makes the diode D1 forward biased. Hence current i1 flows through the load resistor from A to B. Therefore, positive half cycles flows to the output. When the negative half cycle of the input voltage is applied, the point M at the transformer secondary becomes negative with respect to the point N. This makes the diode D2 forward biased. Hence current i2 flows through the load resistor from A to B. Therefore, the positive half cycles flows in the output, even during the negative half cycles of the input. Disadvantages Location of center-tapping is difficult The dc output voltage is small PIV of the diodes should be high (ii) Bridge Full-Wave Rectifier This is such a full wave rectifier circuit which utilizes four diodes connected in bridge form. There is no need of any center-tapping of the transformer in this circuit. Four diodes called D1, D2, D3 and D4 are used in constructing a bridge type network so that two of the diodes conduct for one half cycle and two conduct for the other half cycle of the input supply. When the positive half cycle of the input supply is given, point P becomes positive with respect to the point Q. This makes the diode D1 and D3 forward biased while D2 and D4 reverse biased. Hence the diodes D1 and D3 conduct during the positive half cycle of the input supply to produce the output along the load resistor. As two diodes work in order to produce the output, the voltage will be twice the output voltage of the center tapped full wave rectifier. When the negative half cycle of the input supply is given, point P becomes negative with respect to the point Q. This makes the diode D1 and D3 reverse biased while D2 and D4 forward biased. The current flows through the load in the same direction as during the positive half cycle of the input. Advantages No need of center-tapping. The dc output voltage is twice that of the center-tapper FWR. PIV of the diodes is of the half value that of the center-tapper FWR. The design of the circuit is easier with better output. Video Content / Details of website for further learning (if any): 1. https://www.tutorialspoint.com/electronic_circuits 2. https://www.electronicshub.org 3. https://nptel.ac.in/courses/117103063 Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (619-628) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L – 7B LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Clippers Introduction: A Clipper circuit is a circuit that rejects the part of the input wave specified while allowing the remaining portion. The portion of the wave above or below the cut off voltage determined is clipped off or cut off. The clipping circuits consist of linear and non-linear elements like resistors and diodes but not energy storage elements like capacitors. Prerequisite knowledge for Complete understanding and learning of Topic: PN Diode, Biasing Detailed content of the Lecture: Clipper Circuits A Clipper circuit is a circuit that rejects the part of the input wave specified while allowing the remaining portion. The main advantage of clipping circuits is to eliminate the unwanted noise present in the amplitudes. These can work as square wave converters, as they can convert sine waves into square waves by clipping. The amplitude of the desired wave can be maintained at a constant leve (i) Positive Series Clipper A Clipper circuit in which the diode is connected in series to the input signal and that attenuates the positive portions of the waveform, is termed as Positive Series Clipper. Positive Cycle of the Input When the input voltage is applied, the positive cycle of the input makes the point A in the circuit positive with respect to the point B. This makes the diode reverse biased and hence it behaves like an open switch. Thus the voltage across the load resistor becomes zero as no current flows through it and hence V0 will be zero. Negative Cycle of the Input The negative cycle of the input makes the point A in the circuit negative with respect to the point B. This makes the diode forward biased and hence it conducts like a closed switch. Thus the voltage across the load resistor will be equal to the applied input voltage as it completely appears at the output V0. (ii)Positive Shunt Clipper (iii)Negative Series Clipper The Clipper circuit that is intended to attenuate negative portions of the input signal can be termed as a Negative Clipper. A Clipper circuit in which the diode is connected in series to the input signal and that attenuates the negative portions of the waveform, is termed as Negative Series Clipper. Positive Cycle of the Input When the input voltage is applied, the positive cycle of the input makes the point A in the circuit positive with respect to the point B. This makes the diode forward biased and hence it acts like a closed switch. Thus the input voltage completely appears across the load resistor to produce the output V0. Negative Cycle of the Input The negative cycle of the input makes the point A in the circuit negative with respect to the point B. This makes the diode reverse biased and hence it acts like an open switch. Thus the voltage across the load resistor will be zero making V0 zero. (iv)Negative Shunt Clipper A Clipper circuit in which the diode is connected in shunt to the input signal and that attenuates the negative portions of the waveform, is termed as Negative Shunt Clipper. (v)Biased Clipper : Positive Clipper with negative Vr (vi)Biased Clipper : Positive Clipper with positive Vr (vii)Negative Series Clipper with positive Vr (viii)Negative Series Clipper with negative Vr Video Content / Details of website for further learning (if any): 1. https://www.tutorialspoint.com/electronic_circuits 2. https://www.electronicshub.org 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (619-628) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-8 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Clampers, Avalanche Breakdown Mechanism Introduction: A Clamper Circuit is a circuit that adds a DC level to an AC signal. Actually, the positive and negative peaks of the signals can be placed at desired levels using the clamping circuits. As the DC level gets shifted, a clamper circuit is called as a Level Shifter. Prerequisite knowledge for Complete understanding and learning of Topic: PN diode, Capacitor, Biasing Detailed content of the Lecture: Clamper circuit Clamper circuits consist of energy storage elements like capacitors. A simple clamper circuit comprises of a capacitor, a diode, a resistor and a dc battery if required. A Clamper circuit can be defined as the circuit that shifts the waveform to a desired DC level without changing the actual appearance of the applied signal. In order to maintain the time period of the wave form, the Ʈ must be greater than, half the time period of the capacitor. [ Ʈ = RC ] The time constant of charge and discharge of the capacitor determines the output of a clamper circuit. The DC component present in the input is rejected when a capacitor coupled network is used as a capacitor blocks dc as a capacitor blocks dc. Hence when dc needs to be restored, clamping circuit is used. Positive Clamper Circuit When a negative peak of the signal is raised above to the zero level, then the signal is said to be positively clamped. A Positive Clamper circuit is one that consists of a diode, a resistor and a capacitor and that shifts the output signal to the positive portion of the input signal. Initially when the input is given, the capacitor is not yet charged and the diode is reverse biased. During the negative half cycle, at the peak value, the capacitor gets charged with negative on one plate and positive on the other. The capacitor is now charged to its peak value Vm. The diode is forward biased and conducts heavily. During the next positive half cycle, the capacitor is charged to positive Vm while the diode gets reverse biased and gets open circuited. The output of the circuit at this moment will be V0 = Vi + Vm Hence the signal is positively clamped as shown in the figure. The output signal changes according to the changes in the input, but shifts the level according to the charge on the capacitor, as it adds the input voltage. Positive Clamper with Positive Vr A Positive clamper circuit if biased with some positive reference voltage, that voltage will be added to the output to raise the clamped level. Positive Clamper with Negative Vr A Positive clamper circuit if biased with some negative reference voltage, that voltage will be added to the output to raise the clamped level. Negative Clamper A Negative Clamper circuit is one that consists of a diode, a resistor and a capacitor and that shifts the output signal to the negative portion of the input signal. During the positive half cycle, the capacitor gets charged to its peak value Vm. The diode is forward biased and conducts. During the negative half cycle, the diode gets reverse biased and gets open circuited. The output of the circuit at this moment will be V0 =Vi + Vm Hence the signal is negatively clamped as shown in the figure. Avalanche Breakdown Avalanche Breakdown occurs due to avalanche multiplication. It occurs when the doping concentration is less of order 1 to 10 8. Under Reverse bias, the thermally generated carrier crosses the depletion region and acquires Kinetic energy from the applied voltage. This carrier collides with the crystal and disrupts the covalent band. This is known as Impact Ionization. The new electron hole pair will be created apart from original carrier. The new carrier in turn collide with another crystal by acquiring enough energy from applied field will create electron hole pair. This process continues result in avalanche multiplication. This causes Breakdown known as avalanche Breakdown. Zener Breakdown This breakdown occurs in the heavily doped P and N region. When the strong electric field is applied, the direct rupture of covalent bond takes place produce new electron hale pair. The new electron hale pair so created will increases the reverse current. This reverse current increase at almost 6 volts for heavily doped diode at the field of order 2×107 v/m. This kind of breakdown occurs in heavily doped PN region is known as zener breakdown. Zener Breakdown occur less than 6 V where as Avalanche Breakdown occur greater than 6V. Video Content / Details of website for further learning (if any): 1. https://www.tutorialspoint.com/electronic_circuits 2. https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (560-563) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L-9 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Teacher : Dr. J.RANGARAJAN Unit I : SEMICONDUCTOR DIODES Date of Lecture: Topic of Lecture: Zener Diode as a Voltage Regulator Introduction: Zener diode is a special purpose semiconductor PN junction device made of silicon, which is designed to operate in reverse biased condition by varying the doping concentration. Prerequisite knowledge for Complete understanding and learning of Topic: PN junction, Diode, Doping , Biasing Detailed content of the Lecture: Zener Diode: The doping concentration of the Zener diode is high than the ordinary diode. The silicon high power dissipation characteristic and doping concentration of the zener diode makes the diode to prefer for Reverse bias condition. When the breakdown occur, the current increases whereas the voltage remain Constant (very small change). This phenomenon makes the Zener diode to work as voltage Regulator. The forward bias characteristics of the zener diode will be similar to the PN junction diode when the cut in voltage reaches, the current starts to increases with respect to the voltage. In the Reverse bias condition, because of high doping concentration the breakdown occurs very quickly and once the breakdown occur the current rises sharply whereas the voltage remains more (or) less constant. Characteristics of Zener Diode Applications: Zener Diode is used as Voltage Regulator, Waveform clipper, Voltage shifter and Reference voltage in electronic circuits. Voltage Regulator: Voltage Regulator is an electronic circuit which provides constant voltage level independent of the current in the load. Line Regulator − A regulator which regulates the output voltage to be constant, in spite of input line variations, it is called as Line regulator. Load Regulator − A regulator which regulates the output voltage to be constant, in spite of the variations in load at the output, it is called as Load regulator. Zener Regulator - Working of Zener Voltage Regulator If the applied input voltage Vi is increased beyond the Zener voltage Vz, then the Zener diode operates in the breakdown region and maintains constant voltage across the load. The series limiting resistor Rs limits the input current. Case 1 − If the load current IL increases, then the current through the Zener diode IZ decreases in order to maintain the current through the series resistor RS constant. The output voltage Vo depends upon the input voltage Vi and voltage across the series resistor RS. Vo = Vin – Is Rs Where Is is constant. Therefore, Vo also remains constant. Case 2 − If the load current IL decreases, then the current through the Zener diode IZ increases, as the current IS through RS series resistor remains constant. Though the current IZ through Zener diode increases it maintains a constant output voltage VZ, which maintains the load voltage constant. Case 3 − If the input voltage Vi increases, then the current IS through the series resistor RS increases. This increases the voltage drop across the resistor, i.e. VS increases. Though the current through Zener diode IZ increases with this, the voltage across Zener diode VZ remains constant, keeping the output load voltage constant. Case 4 − If the input voltage decreases, the current through the series resistor decreases which makes the current through Zener diode IZ decreases. But the Zener diode maintains output voltage constant due to its property. Limitations of Zener Voltage Regulator It is less efficient for heavy load currents. The Zener impedance slightly affects the output voltage. Video Content / Details of website for further learning (if any): 1. https://www.tutorialspoint.com/electronic_circuits 2. https://www.physics-and-radio-electronics.com/electronic-devices-and-circuits 3. https://nptel.ac.in/courses/117103063/ Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar and A.Vallavaraj, Tata McGraw Hill, 2nd Edition, 2008. (123-125) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Teacher Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L 10 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Faculty : Dr. J.Rangarajan Unit : II - Bipolar Junction Transistors Date of Lecture: Lecture Topic of Lecture: Bipolar Junction Transistor T Operation Introduction: Transistor is a three terminal semiconductor devices (Base, emitter and collector) that can be used to switch and amplify plify electronic signals such aass radio and television signals. The amplification in the transistor is achieved by passing input current from a region of low resistance to a region of high resistance, hence it is known as Transfer – resistor (Transistor) Prerequisite knowledge for Complete understanding and learning of Topic: Atomic structure Energy band diagram Diode Bipolar Junction Transistor Operation TYPES OF TRANSISTORS There are two basic types of transistors (i) Unipolar Junction Transistor: In this type, the he current conduction is due to one type of carrier that is majority carrier. carrier (ii) Bipolar junction Transistor: In this type, the current conduction is due to both types of charge carriers that is majority major as well as minority carrier. The Bipolar junction transistors are of two types (a) PNP transistor (b) NPN transistor CONSTRUCTION OF PNP AND NPN TRANSISTOR (a) PNP Transistor: When the transistor is formed by sandwiching a single nn-region region between two p - region, then it is known as PNP transistor. PNP transistor Emitter Collecto E P N P r C B Base Symbol Two diode transistor version E C B C B B (b) NPN Transistor: When the transistor is formed by sandwiching a single p – region between two n – region then it is known as NPN transistor. NPN transistor Emitter Collecto E N P N r C B Base Symbol Two diode transistor version E C E C B B From the above figures, we can understand that the Transistor has two junctions One junction is formed between Emitter and base, and it is called Emitter – Base junction. Other junction is formed between Base and Collector, and it is called Collector – Base junction. It has three terminals. Emitter: The emitter is heavily doped. The main function of the emitter is to inject a large number of charge carriers into the base. The arrow head is always at the collector which indicates the conventional direction of current flow. Base: The Base is lightly doped middle region and very thin. The main function of the base is to pass most of the injected charge carriers into the collector. Collector: The collector is moderately doped. The main function of the collector is to collect the charge carriers. Since it dissipate more power, it is physically larger than emitter region. BIASING Applying external voltage of correct polarity and magnitude to the two junction of the transistor is called Biasing Transistor Biasing Based on the external voltage polarity, the transistor will be operated in three different regions. That is (i) Active region (ii) Cutoff region and (iii) Saturation region Emitter Base Collector Base Region junction junction Application Active Forward biased Reverse biased Amplifier Cut off Reverse biased Reverse biased Open switch Suration Forward biased Forward biased closed switch OPERATION OF AN NPN TRANSISTOR Normally the transistor will be biased in active region. Hence Emitter base is forward biased and collector base is reverse biased. Biasing the NPN Transistor E C N P N B – + – + VEB VEB The applied forward bias causes the lot of electrons from the emitter region to enter into the base region and this causes the forward current flow due to majority carrier electrons. Since the base is lightly doped with P – type impurity, the injected electron from the emitter Combines with the holes in the P – type region to Constitute a base current (IB) Few electron combines with holes and the remaining electrons (more than 95%) crossover the base region into collector region to Contribute Collector Current(IC) Collector is reverse biased and hence they collects the diffused electrons which enters the collector junction. The magnitude of emitter current IE = IB + IC OPERATION OF AN PNP TRANSISTOR Biasing the PNP Transistor E C P N P B + – + – The applied forward bias causes lot of holes from the emitter region to enter into the base region and this causes the forward current flow due to majority carrier holes. Since the base is lightly doped with n type impurity, the injected holes from the emitter combines with the electrons in the n type region to constitute a base current(IB) Few holes combines with electron and the remaining holes (more than 95%) cross over the base region into collector region to Contribute Collector Current Collector is reverse biased and hence they collects the diffused holes which enters the collector junction(IC) The magnitude of emitter Current IE = IB + I Video Content / Details of website for further learning (if any): 1. https://www.elprocus.com/using-transistor-as-a-switch/ 2. httphttps://circuitglobe.com/transistor-as-an-amplifier.html 3. https://nptel.ac.in/courses/117103063/ 4. httphttps://circuitglobe.com/transistor-as-an-amplifier.htmls://www.electronics- tutorials.ws/amplifier/amp_2.htmlbuild-electronic-cir Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar, &A.Vallavaraj Tata McGraw Hill, Second Edition, 2008. (151-152) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Faculty Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L 11 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Faculty : Dr. J.Rangarajan Unit : II - Bipolar Junction Transistors Date of Lecture: Topic of Lecture: Common Base Configuration Introduction: In this configuration, the input is given between emitter and base and output is taken between collector and base The emitter base junction is forward biased and collector base junction is reversed biased. Hence IE (Emitter Current) flows in the input circuit and IC (collector Current) flows in the output circuit. Prerequisite knowledge for Complete understanding and learning of Topic: Diode operation Transistor Operation Common Base Configuration Characteristics cteristics of CB Configuration: The performance of the transistor Configuration can be determined from the static characteristics curves, which relates the different dc currents and voltage of the transistor. Circuit to determine CB static characteristics (Input and Output characteristics) IE (mA) IC (mA) E C A _ A _ + + B _ + _ IB + VEE V V VCC VCB _ _ + + VEB Input Characteristics: The input characteristics of the CB configuration is determined by increasing the emitter current IE from zero by increasing VEB, keeping VCB constant. The input curve is obtained are shown Input characteristics curve IE(mA) VCB> VCB=0 4 1 v 3 2 1 VEB(v) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 For the given value of VCB and increase in the VEB, the emitter base junction is forward biased. The value of IE increases when the values of VEB increase similar to forward biased diode. When VCB increased, the width of the base region will decrease which result in increases in the value of IE much earlier for increases in VEB. This makes the curve to shift left. Output characteristics: The output characteristics of the CB configuration is determined by increasing the collector current IC by increasing VCB, keeping IE constant at a suitable value by adjusting VEB. This step is repeated for various fixed values of IE. The curves obtained are shown below. Output characteristics curve IC Active (mA) region Saturation region IE=2mA IE=1m A IB=0mA VCB(v) Cutoff region Two important characteristics can be observed from the output graph. (i) For a constant value of IE, Ic is independent of VCB and the curves are parallel to the axis of the VCB. (ii) IC flows even when VCB = 0, the majority carrier electron from the emitter base forward biased junction will injected into the collector base junction due to internal potential barrier at the reversed biased collector base junction. Early effect (or) Base width Modulation When the collector voltage is increased, the width of the depletion region increases as the reverse bias voltage increases. This increase in the depletion region decreases the width of the Base. This phenomenon of variation in the Base width with respect to the variation of collector voltage is known as Base width modulation (or) Early effect. The value of increases for large value of VCC (or) early effect. Punch Through When the value of collector voltage is extremely large, the effective base width will reduces to zero leads to the voltage breakdown in the transistor. This phenomenon is known as Punch through. Transistor equation If there is no ac signal, then the ratio of IC to IE is known as dc amplification factor I dc C IE (Since IC flows into transistor & IE flows out of transistor) The ratio of charge in collector current to the change in emitter current is known as current amplification factor (α). IC ac , VCB Constant I E The collector current depends upon two factors (i) amplified emitter current (IE) (ii) leakage current due to movement of minority carrier across output (ICBO) Hence Collector Current IC I E ICBO We know that IE = IB + IC Hence IB = IE – IC ----------- (1) Sub IC in (1) IB = IE – (IE + ICBO) IB = IE – IE - ICBO IB = IE (1-)-ICBO Transistor Parameters: Four transistor parameters can be determined from CB characteristics curve, they are known as common base hybrid parameters (or) h parameters. (a) Input Impedance (hib): It is the ratio of the change in emitter voltage to the change in emitter current, keeping VCB constant. V hib EB , VCB Constant IE (b) Output admittance (hob): It is the ratio of the change in collector current to the change in the collector voltage, keeping IE constant. I C hob , IE Constant VCB (c) Forward current gain (hfb): It is the ratio of the change in the collector current to the change in the Emitter Current keeping V CB constant I hfb C , VCB Constant I E (d) Reverse Voltage gain (hrb): If is the ratio of the change in the Emitter voltage to the change in the collector voltage, keeping IE constant. V hrb EB , I E Constant VCB Video Content / Details of website for further learning (if any): 1. https://www.elprocus.com/using-transistor-as-a-switch/ 2. https://circuitglobe.com/transistor-as-an-amplifier.html 3. https://nptel.ac.in/courses/117103063/ 4. httphttps://circuitglobe.com/transistor-as-an-amplifier.htmls://www.electronics- tutorials.ws/amplifier/amp_2.htmlbuild-electronic-cir Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar, &A.Vallavaraj Tata McGraw Hill, Second Edition, 2008. (172-174) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Faculty Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L 12 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Faculty : Dr. J.Rangarajan Unit : II - Bipolar Junction Transistors Date of Lecture: Topic of Lecture: Common Emitter Configuration Introduction Hence IB (Base In this configuration, the input is given between emitter and base and output is taken between collector and emitter. Emitter base junction is forward biased, whereas the emitter collector junction is reversed biased current) flows in the input circuit and IC (Collector current) flows in the output circuit. Prerequisite knowledge for Complete understanding and learning of Topic: Diode operation Transistor Operation Common Emitter Configuration Characteristics of CE Configuration The circuit diagram for CE configuration is given below Circuit to determine CE static characteristics (Input and Output characteristics) I (mA) _C + A C IB(A) A B + _ E + + + + VBB V V _ _ V IE VCE _ _ VCC BE The performance of the CE configuration can be determined from the static characteristic curve. Input characteristics:- The input characteristics of CE configuration are determined by increasing the base current IB from zero by increasing VEB, keeping VCE constant. This step is repeated for various fixed values of VCE.The input curve obtained are shown below Input characteristics curve IE(A) VCE=0v VCE>0v 200 150 100 50 VBE(v) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 For the given value of VCE and increasing the value of VBE, the base current IB increased, Input characteristics of the CE configuration is similar to CB configuration, where the Emitter base is forward biased. Hence increases in VBE increases IB. But when VCE is increased, the width of the depletion region increases due to reverse bias which makes the effective width of the base to decreases which in turn decreases IE. Therefore the curve shifts to the right. Output characteristics: The output characteristics of the CE configuration is determined by increasing the collector current IC by increasing VCE, keeping IB constant at a suitable value by adjusting VCB. This step is repeated for various fixed values of IB. The curves obtained are shown below. Output characteristics curve IC (mA) Saturation region IB=60A IB=40A IB=20A IB=0A VCE(v) Cutoff region The output characteristics have three regions namely (i) Active region: In this region, curves are uniform in spacing increases in the collector voltage increases I C here for large value of IB, IC is larger than IB. Thus current gain is greater than unity makes the transistor to be uses as an amplifier. (ii) Saturation region: For low values of VCE, the transistor operates in this region. Increase in the base current IB does not cause a corresponding change in IC. (iii)Cutoff Region: In this region, the collector current becomes almost zero and small amount of collector current flows even when IB=0. This is called ICEO. Transistor equation The ratio of change in collector current to change in base current is known as current amplification factor . I C , VCE Constant I B We know that IE = IB+IC IC =IE + ICBO ------------ (1) Sub IE in eqn (1) IC = (IB +IC) + ICBO = IB +IC + ICBO IC - IC = IB + ICBO IC (1- ) = IB + ICBO 1-on both sides I IC IB CBO ------------ (2) 1- 1 We already know IC IB ICEO ----------- (3) Hence comparing (2) & (3) I and I CEO CBO 1- 1 I C I B ( 1)I CBO Transistor Parameters Four transistor parameters can be determined from CE configuration curve. They are known as common emitter hybrid parameters (or) h parameters. (a) Input Impedance (hie) It is the ratio of the change in base voltage to the change in Base current, keeping VCE constant. V h ie BE , VCE Constant I B (b) Output admittance (hoe) It is the ratio of the change in collector current to the change in collector voltage keeping base current constant. I C h oe , I B Constant VCE (c) Forward current gain (hfe) It is the ratio of the change in collector current to the change in the base current, keeping VCE constant. I h fe C , VCE Constant I B (d) Reverse Voltage gain (hre) It is the ratio of the change in the base voltage to the change in the collector Voltage, keeping IB constant. V h re BE , I B Constant VCE Video Content / Details of website for further learning (if any): 1. https://www.elprocus.com/using-transistor-as-a-switch/ 2. httphttps://circuitglobe.com/transistor-as-an-amplifier.html 3. https://nptel.ac.in/courses/117103063/ 4. httphttps://circuitglobe.com/transistor-as-an-amplifier.htmls://www.electronics- tutorials.ws/amplifier/amp_2.htmlbuild-electronic-cir Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar, &A.Vallavaraj Tata McGraw Hill, Second Edition, 2008. (172-174) 2 “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Faculty Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L 13 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Faculty : Dr. J.Rangarajan Unit : II - Bipolar Junction Transistors Date of Lecture: Topic of Lecture: Common Collector Configuration, Current components Introduction In this configuration, the input is given between base and collector and output is taken between collector and emitter. The base – Collector ollector is forward biased, whereas the emitter collector junction is reversed biased Hence IB (Base current) flows in the input circuit and IE (Emitter current) flows in the output circuit. Prerequisite knowledge for Complete understanding and learning of Topic: Diode operation Transistor Operation Common Collector Configuration Characteristics acteristics of CC configuration The circuit diagram for CC Configuration is given below Circuit to determine CC static characteristics (Input and Output characteristics) IE (mA) IC + A _ IB (A) E B A + _ C + _ + _ VBB VBC V V VEC _ _ IE VEE + + lle The performance of CC configuration can be determined from the static characteristic curve. Input characteristics: The input characteristics of CC configuration are determined by increasing the base current IB from zero by increasing VBC keeping VEC constant. This step is repeated for various fixed values of VEC. The curves obtained are shown below. Input characteristics curve 100 IB (A) 80 VEC = 2V VEC = 4V 60 40 20 1 2 3 4 5 6 VCB The characteristics curve of CC is similar to the CE configuration except the VBC in increased instead of VBE. Output Characteristics: The output characteristics of the CC configuration is determined by increasing the Emitter current (IE) by increasing VEC, keeping IB constant at a suitable value by adjusting VBC. This step is repeated for various fixed values of IB. The curves obtained are shown below. Output Characteristics curve IE (mA) 4 IB=60A 3 IB=40A 2 IB=20A 1 IB=0A 1 2 3 4 5 6 VEC(v) Transistor equation The ratio of change in Emitter Current to the change in Base current is known as Current amplification factor (γ) I dc E , Keeping VCE constant I B The Collector Current IC = IE + ICBO Here, IE = IB + IC -------- (1) sub IC in (1) IE = IB + IE + ICBO IE (1-) = IB + ICBO IE (1-) = IB +ICBO I I I E B CBO 1 1 (a) Relationship between and : I I C WKT, C [since IE = IB + IC] I E I C I B IC & I B 1 I C IB 1 1 Hence 1 I C 1 (b)Relationship between, and :- I E I E Current gain = (since IE =IB + IC) I B I E I C Dividing numerator & Denominator by IC I E IC I E 1 IC 1 1 I WKT C I E 1 1 1 1 1 1 COMPARISON OF TRANSISTOR CONFIGURATIONS Characteristic Common Base Common emitter Common Collector Input Resistance Very low (20) Low (1 k ) High (400 k ) Output Resistance Very high (400k) High (45 k ) Low (30) Input Current IE IB IB Output Current IC IC IE Input voltage Emitter Base Base Emitter Base collector applied output voltage Collector Base Collector emitter Emitter collector taken voltage gain About 150 About 500 Less than 1 Current gain Unity Current gain High Very high Current I I I amplification factor dc C dc C dc E IE IB IB Application high frequency Audio frequency Impedance circuit circuits matching circuit Video Content / Details of website for further learning (if any): 1. https://www.elprocus.com/using-transistor-as-a-switch/ 2. httphttps://circuitglobe.com/transistor-as-an-amplifier.html 3. https://nptel.ac.in/courses/117103063/ 4. httphttps://circuitglobe.com/transistor-as-an-amplifier.htmls://www.electronics- tutorials.ws/amplifier/amp_2.htmlbuild-electronic-cir Important Books/Journals for further learning including the page nos.: 1. “Electronic Devices and Circuits”, S.Salivahanan, N.Sureshkumar, &A.Vallavaraj Tata McGraw Hill, Second Edition, 2008. (172-174) 2. “Electronic Devices”, Thomas L.Floyd, Prentice Hall, Ninth Edition, 2012. (Unit 1 and 2) Course Faculty Verified by HOD MUTHAYAMMAL ENGINEERING COLLEGE (An Autonomous Institution) (Approved by AICTE, New Delhi, Accredited by NAAC & Affiliated to Anna University) Rasipuram - 637 408, Namakkal Dist., Tamil Nadu L 14 LECTURE HANDOUTS ECE I / II Course Name with Code : 19GES11 - ELECTRONIC DEVICES Course Faculty : Dr. J.Rangarajan Unit : II - Bipolar Junction Transistors Date of Lecture: Topic of Lecture: Ebermoll’s model Introduction When the collector voltage is increased, the width of the depletion region increases as the reverse bias voltage increases. This increase in the depletion region decreases the width of the B Brase. ase. This phenomenon of variation in the Base width with respect to the variation of collector voltage is known as Base width modulation (or) early effect. The value of increases for large value of VCC (or) early effect. Prerequisite knowledge for Complete understanding and learning of Topic: Transistor Operation Configuration Eber’s moll model Eber’s moll model is commonly used for large signal analysis and switching application It is the steady state model helps to analyze the conduction of the various model of the transistor Current direction and Voltage polarity direction for Ebers moll model E circuit: C Basic Eber’s moll equivalent circuit:- RI FIF IE IC E C VB VB – + + – IF IR eVkTBE 1 eVkTBC 1 I F I ES exp I R ICS exp B According to the current equation referred by Kirchhoff’s current law l I E + I B + IC = 0 ------- (1) &I =-I –I The collector current is given as IC = FIF – IR ------- (2) qVBE Where If =IES [ e kT -1] qVBC and IR = ICS [ e kT -1] Hence sub IF& IR in eqn (2), we get qVBC I C F I ES e kT 1 I CS e kT 1 qVBE ------- (3) ly The Emitter Current is given as R = Common base IE = RIR – IF ------- (4) current in Reverse active Sub IF & IR in equ (4), we get mode qVBC kT qVBE kT I E R ICS e 1 I ES e 1 ------- (5) Equation (3) & (5) are classic Ebers moll – equations Eber’s moll model has four parameters: F, R, IES & ICS a F IES a R ICS ------- (6) In this model, Let us determine the Ebers moll equation for the transistor in saturation mode. We know that, saturation Voltage as VCE sat VBE VBC ------- (7) In the saturation mode, VBE >0, & VBC > 0 since both BE & BC junction are forward bias. VBE Expression From equation (5) qVBC qVBE I E R ICS e kT 1 I ES e kT 1 We know that IE = - (IB + IC), hence sub this in above equation qVBC qVBE (I B I C ) R I CS e kT 1 IES e kT 1 RICS e kT 1 IB IC IES e kT 1 qVBC qVBE I I I e qVBE kT 1 qVBC B C ES e kT 1 ------- (8) R I CS Sub eqn (8) in eqn (3), we get IB IC IES e kT 1 qVBE IC F IES e kT 1 ICS qVBE I R CS ICR FIESR e I I I I eqV kT I qVBE BE kT F ES R B C ES ES eqV kT I I I 1 I I 1 ES F R ES C R B ES F R BE qVBE IC 1 R IB IES 1 F R e kT IES 1 FR Taking ln on both sides, we get qVBE I 1 R I B I ES 1 F R ln C KT IES 1 F R IC 1 R IB I ES 1 F R Hence VBE Vt ln ------- (9) I ES 1 F R KT Vt =Thermal voltage q VBC Expression: From equation (3) IC FIES e 1 ICS e 1 qVBE qVBC kT kT I I eqVBC kT 1 C CS eqVBE kT 1 FIES ------- (10) Sub eqn (10) in (5) and also substituting IE = -IB – IC, we get IES IC ICS e qV BC kT 1 1 qV BC IB IC RICS e kT FIES IB IC F F R ICS e qVBC kT qVBC R ICS F I C I CS e ICS kT qVBC Taking e kT term on left side we get qVBC e kT R F ICS ICS IB F IC ( F 1) ICS (1 R F ) qVBC I B F I C ( F 1) ICS (1 R F ) e kT I CS (1 F R ) Taking ln on both sides qVBC I I ( 1) I CS (1 F R ) ln B F C F KT ICS (1 F R ) KT I B F IC ( F 1) ICS (1 F R ) VBC ln q I CS (1 F R ) I I ( 1) ICS (1 F R ) VBC VT ln B F C F ------ (11) ICS (1 F R ) Now VCE (Sat) = VBE-VBC Sub eqn (9) & (11) by neglecting IES & ICS term we get IC (1 R ) IB I I ( 1) VCE (sat) V
