Note for ELECTRONIC CIRCUIT ANALYSIS - ECA By JNTU Heroes

Topics ( 8 )

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Electronic Circuits Table of Contents Unit – 1: Transistor, UJT‟s, and Thyristors............................................................................ 3 1.1 Operating Point ........................................................................................................... 3 1.2 The Common Emitter (CE) Configuration ................................................................... 7 1.3 The Transistor as a Switch ......................................................................................... 20 1.4 Silicon-Controlled Rectifiers, or SCRs ...................................................................... 27 1.5 The Gate Turn-Off Thyristors (GTO) ........................................................................ 28 1.6 Recommended Questions .......................................................................................... 37 Unit – 2: Bipolar Junction Transistors ................................................................................. 38 2.1 Bipolar junction transistor (BJT)................................................................................ 38 2.2 The Field Effect Transistor ........................................................................................ 43 2.3 The Junction Field Effect Transistor .......................................................................... 44 2.4 Comparison of connections between a JFET and a BJT ............................................. 44 2.5 JFET Amplifier ......................................................................................................... 49 2.6 CMOS ....................................................................................................................... 50 2.7 Recommended Questions .......................................................................................... 52 Unit – 3: Photodiodes .......................................................................................................... 53 3.1 Photodiodes ............................................................................................................... 53 3.2 PN Photodiode .......................................................................................................... 53 3.3 PIN Photodiode ......................................................................................................... 54 3.4 Schottky Photodiode.................................................................................................. 54 3.5 Phototransistors ......................................................................................................... 56 3.6 Light-Emitting Diodes (LED) .................................................................................... 58 3.7 Cathode Ray Tube Displays....................................................................................... 63 3.8 Emerging Display Technologies ................................................................................ 64 3.9 Optocouplers ............................................................................................................. 65 3.10 Recommended Questions......................................................................................... 67 UNIT – 4: Small Signal Analysis of Amplifiers................................................................... 68 4.1 Basic FET Amplifiers ................................................................................................ 68 4.2 THE MOSFET AMPLIFIER ..................................................................................... 68 4.3 Small-Signal Equivalent Circuit................................................................................. 74 4.4 Problem-Solving Technique: MOSFET AC Analysis ................................................ 76 4.5 Basic Transistor Amplifier Configurations................................................................. 78 4.6 The Source-Follower Amplifer .................................................................................. 87 4.7 Input and Output impedance ...................................................................................... 90 4.8 The Common-Gate Configuration.............................................................................. 91 Page 1

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Electronic Circuits 4.9 The Three Basic Amplifier Configurations: Summary and Comparison ..................... 95 4.10 Recommended Questions......................................................................................... 99 Unit – 5: Large Signal Amplifiers ..................................................................................... 100 5.1 Classification of Large Signal Amplifiers ................................................................ 100 5.2 Large signal Amplifier Characteristics ..................................................................... 102 5.3 Feedback Amplifiers ............................................................................................... 103 5.4 Stability of Gain Factor ........................................................................................... 105 5.5 Feedback Topologies ............................................................................................... 107 5.6 Recommended Questions ........................................................................................ 108 UNIT – 6: Sinusoidal Oscillators....................................................................................... 109 6.1 Principles of oscillators............................................................................................ 109 6.2 Phase shift Oscillator ............................................................................................... 114 6.3 Band Pass Oscillators .............................................................................................. 120 6.4 Wien Bridge Oscillator ............................................................................................ 123 6.5 Colpitts and Hartley Oscillators ............................................................................... 126 6.6 Piezoelectric Crystal Oscillators .............................................................................. 133 6.7 Recommended Questions ........................................................................................ 146 UNIT – 7: Linear Power Supplies, Switched mode Power Supplies ................................... 147 7.1 Regulated power supply .......................................................................................... 147 7.2 POWER SUPPLY FILTER ..................................................................................... 147 7.3 Fixed Positive Linear Voltage Regulators ................................................................ 149 7.4 The Regulated Dual Voltage DC Power Supply ....................................................... 153 7.5 Recommended Questions ........................................................................................ 155 UNIT – 8: Operational Amplifier ...................................................................................... 156 8.1 Operational Amplifier (Op-Amp) ............................................................................ 156 8.2 Ideal Op-Amp.......................................................................................................... 157 8.3 Applications of Opamp ............................................................................................ 159 8.4 Instrumentation Amplifier ....................................................................................... 167 8.5 Relaxation Oscillator ............................................................................................... 169 8.6 Current-to-Voltage Converter .................................................................................. 169 8.7 Voltage-to-Current Converter .................................................................................. 170 8.8 Exercise Problems ................................................................................................... 171 8.9 Recommended Questions ........................................................................................ 173 Page 2

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Electronic Circuits Unit – 1: Transistor, UJT’s, and Thyristors In the Diode tutorials we saw that simple diodes are made up from two pieces of semiconductor material, either silicon or germanium to form a simple PN-junction and we also learnt about their properties and characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series that share a common P or N terminal. The fusion of these two diodes produces a three layer, two junctions, and three terminal devices forming the basis of a Bipolar Junction Transistor, or BJT for short. 1.1 Operating Point Operating Regions The pink shaded area at the bottom of the curves represents the "Cut-off" region while the blue area to the left represents the "Saturation" region of the transistor. Both these transistor regions are defined as: 1. Cut-off Region Here the operating conditions of the transistor are zero input base current (IB), zero output collector current (IC) and maximum collector voltage (VCE) which results in a large depletion layer and no current flowing through the device. Therefore the transistor is switched "FullyOFF". Page 3

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Electronic Circuits Cut-off Characteristics The input and Base are grounded (0v) Base-Emitter voltage VBE < 0.7V Base-Emitter junction is reverse biased Base-Collector junction is reverse biased Transistor is "fully-OFF" (Cut-off region) No Collector current flows ( IC = 0 ) VOUT = VCE = VCC = "1" Transistor operates as an "open switch" Then we can define the "cut-off region" or "OFF mode" when using a bipolar transistor as a switch as being, both junctions reverse biased, IB < 0.7V and IC = 0. For a PNP transistor, the Emitter potential must be negative with respect to the Base. 2. Saturation Region Here the transistor will be biased so that the maximum amount of base current is applied, resulting in maximum collector current resulting in the minimum collector emitter voltage drop which results in the depletion layer being as small as possible and maximum current flowing through the transistor. Therefore the transistor is switched "Fully-ON". Saturation Characteristics The input and Base are connected to VCC Base-Emitter voltage VBE > 0.7V Base-Emitter junction is forward biased Base-Collector junction is forward biased Transistor is "fully-ON" (saturation region) Max Collector current flows (IC = Vcc/RL) VCE = 0 (ideal saturation) VOUT = VCE = "0" Transistor operates as a "closed switch" Then we can define the "saturation region" or "ON mode" when using a bipolar transistor as a switch as being, both junctions forward biased, IB > 0.7V and IC = Maximum. For a PNP transistor, the Emitter potential must be positive with respect to the Base. Then the transistor operates as a "single-pole single-throw" (SPST) solid state switch. With a zero signal applied to the Base of the transistor it turns "OFF" acting like an open switch and zero collector current flows. With a positive signal applied to the Base of the transistor it turns "ON" acting like a closed switch and maximum circuit current flows through the device. An example of an NPN Transistor as a switch being used to operate a relay is given below. With inductive loads such as relays or solenoids a flywheel diode is placed across the load to dissipate the back EMF generated by the inductive load when the transistor switches "OFF" and so protect the transistor from damage. If the load is of a very high current or voltage nature, such as motors, heaters etc, then the load current can be controlled via a suitable relay as shown. Page 4