Basic Electronics Fundamentals (Part 66–B04) PDF - Air Service Training Oct 2024

B2-04 Basic Electronic Fundamentals Air Service Training © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals © Air Service Training (Engineering) Ltd Aeronautical Engineering Training Notes These training notes have been issued to you on the understanding that they are intended for your guidance, to enable you to assimilate classroom and workshop lessons and for self-study. Although every care has been taken to ensure that the training notes are current at the time of issue, no amendments will be forwarded to you once your training course is completed. It must be emphasised that these training notes do not in any way constitute an authorised document for use in aircraft maintenance. Document Quality Air Service Training (Engineering) Limited are committed to improving their product and service. Consequently, if you find any errors with this document then please forward them to the document owner at the e-mail address below. [email protected] Initial Issue AL1 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Amendment History Commission Implementation Regulation 2023/989 – Initial Issue Amendment Details of Change Date List (AL) 0 Commission Implementation Regulation 2023/989 June 2024 1 CAA finding NC 26892 – Document detail on EASA/CAA Split Oct 2024 Initial Issue AL1 1 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Material has been added to the notes below to retain compliance with both CAA and EASA post Regulation 2023/989, no content from previous regulations have been removed. Each chapter details the requirements from each authority and the table below details the additions required for EASA post Regulation 2023/989. Students will be taught to the higher level and content then will sit separate exams for each authority, they will only be examined to the relevant syllabus. B1 Sub-module Additions/Level changes 4.1.1a Semiconductors - Materials, Electron configuration, Electrical properties Diodes 4.1.1a Semiconductors - P/N type materials, effects of impurities on conduction, majority and minority characteristics Diodes 4.1.1a Semiconductors - P-N junction in a semi-conductor, development of potential across P-N junction in unbiased, Diodes forward-biased and reverse-biased conditions 4.1.1a Semiconductors - Diode parameters: peak inverse voltage, maximum forward current, temperature, frequency, Diodes leakage current, power dissipation 4.3a Servomechanisms All Sub-module B2 Sub-module Additions/Level changes 4.1.1a Semiconductors - Materials, Electron configuration, Electrical properties Diodes 4.1.1a Semiconductors - P/N type materials, effects of impurities on conduction, majority and minority characteristics Diodes 4.1.1a Semiconductors - P-N junction in a semi-conductor, development of potential across P-N junction in unbiased, Diodes forward-biased and reverse-biased conditions Initial Issue AL1 1 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals 4.1.1a Semiconductors - Diode parameters: peak inverse voltage, maximum forward current, temperature, frequency, Diodes leakage current, power dissipation 4.1.1b Semiconductors - Functional testing of diodes. Diodes 4.1.1b Semiconductors - including types of FET Diodes 4.1.1b Semiconductors - Operation and amplifier stages connecting methods: resistive, capacitive, direct, inverting, non- Diodes inverting and adding. 4.1.3a Semiconductors – All sub-module Integrated circuits 4.3a Servomechanisms All Sub-module 4.3b Servomechanisms Construction, operation and use of servomechanism and PID controller 4.3b Servomechanisms Fault-finding of servo defects, reversal of synchro leads, hunting Initial Issue AL1 2 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Module 4 Basic Electronics Aim The aim of this module is to introduce basic electronic concepts and give an understanding of the components listed in the objectives below. Initial Issue AL1 1 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Objectives Section 1 Diodes 1 Describe the following: a Diode symbols. b Diode characteristics and properties. c Diodes in series and parallel. 2 Describe the characteristics and use of a: a Rectifier diode. b Varistor diode. c Silicon Controlled Rectifier. d Light Emitting Diode. e Photo Conducting Diode. 3 Describe the functional testing of diodes. Section 2 Transistor 1 Describe the following: a Transistor symbols. b Component description and orientation. c Transistor characteristics and properties. Section 3 Integrated Circuits 1 Describe and explain the operation of: a Logic circuits. b Linear circuits. c Operational Amplifiers. Section 4 Printed Circuit Boards 1 Describe Printed Circuit Boards. 2 Explain use of Printed Circuit Boards. Initial Issue AL1 2 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 5 Servo Mechanisms 1 Describe the following: a Open Loop System. b Closed Loop System. c Feedback and Follow up. d Analogue Transducers. 2 Describe the Principle and use of: a Torque Synchros. b Control Synchros. c Differential Synchros. d Transformer Synchros. e Capacitance Transducers. f Inductance Transducers. g Transmitter/Receiver Synchros. Initial Issue AL1 3 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Glossary of Acronyms Used Symbol Description Symbol Description +ve positive Op Amp operational amplifier -ve negative PCB printed circuit board µA micro amp R resistance µV micro volt R1 rotor winding 1 mCd milli candelas R2 rotor winding 2 r polar co-ordinate (distance) RF feedback resistance  polar co-ordinate (angle) RIN input impedance (of operational amplifier) Ω ohms S1 synchro winding 1 ac alternating current S2 synchro winding 2 CMOS Complimentary Metal Oxide S3 synchro winding 3 Semiconductor cos cosine SCR silicon controlled rectifier D diode sin sine dc direct current sw switch DIP dual in-line package tan tangent FET field effect transistor TG tacho-generator Hz Hertz TR transistor I current TTL transistor transistor logic ∆ IB change of input current V voltage ∆ Ic change of output current VFB feedback voltage IC integrated circuit VDS drain/source voltage ID drain current Vf diode voltage If supply current VGS gate/source voltage JUGFET junction gate field effect VIN input voltage transistor K kilo VOUT output voltage LED light emitting diode Vs supply voltage M mega x cartesian co-ordinate (horizontal) max maximum y cartesian co-ordinate (vertical) min minimum MOS metal oxide semiconductor MOSFET metal oxide semiconductor field effect transistor MOV metal oxide varistor Initial Issue AL1 4 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Contents Chapter 1: Diodes.................................................................................................... 7 EASA 2023/989 4.1.1................................................................................................ 7 CAA 1321/2014 4.1.1................................................................................................. 7 Section 1: General Diodes..................................................................................... 7 Section 2: Junction Diodes.................................................................................. 12 Section 3: Rectifier Diode.................................................................................... 27 Section 4: The Varistor........................................................................................ 32 Section 5: Silicon Controlled Rectifier.................................................................. 35 Section 6: Light Emitting Diodes.......................................................................... 39 Section 7: Photo Conductive Diode..................................................................... 49 Chapter 2: Transistors.......................................................................................... 50 EASA 2023/989 4.1.2.............................................................................................. 50 CAA 1321/2014 4.1.2............................................................................................... 50 Section 1: Bi-Polar Transistor.............................................................................. 50 Section 2: Field Effect Transistors (FET)............................................................. 58 Section 3: Photo Transistor................................................................................. 61 Chapter 3: Integrated Circuits.............................................................................. 62 EASA 2023/989 4.1.3.............................................................................................. 62 CAA 1321/2014 4.1.3............................................................................................... 62 Section 1: Integrated Circuit Devices Specifications............................................ 62 Section 2: Integrated Circuit Construction........................................................... 68 Section 3: Integrated Circuit Packages................................................................ 71 Section 4: Linear Integrated Circuits.................................................................... 74 Section 5: Digital Integrated Circuits.................................................................... 85 Chapter 4: Printed Circuit Boards........................................................................ 93 EASA 2023/989 4.2................................................................................................. 93 CAA 1321/2014 4.2.................................................................................................. 93 Section 1: Printed Circuit Board Description........................................................ 93 Section 2: PCB Modular Construction................................................................. 94 Section 3: PCB Construction............................................................................... 96 Section 4: PCB Types.......................................................................................... 97 Section 5: PCB Coatings................................................................................... 100 Chapter 5: Servomechanisms............................................................................ 101 EASA 2023/989 4.3............................................................................................... 101 CAA 1321/2014 4.3................................................................................................ 101 Initial Issue AL1 5 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 1: Transducers...................................................................................... 101 Section 2: Torque Synchros.............................................................................. 105 Section 3: Torque Synchro System................................................................... 107 Section 4: Torque Differential Synchro System................................................. 109 Section 5: Control Synchros.............................................................................. 112 Section 6: Resolver Synchros............................................................................ 116 Section 7: Sensors and Switches...................................................................... 121 Section 8: Capacitor Displacement Transducer................................................. 126 Section 9: Inductance Displacement Transducer.............................................. 129 Section 10: Synchro Identification...................................................................... 130 Chapter 6: Supplementary – Revision Questions............................................ 132 Chapter 1....................................................................................................... 132 Chapter 2....................................................................................................... 134 Chapter 3....................................................................................................... 136 Chapter 4....................................................................................................... 138 Initial Issue AL1 6 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Chapter 1: Diodes EASA 2023/989 4.1.1 CAA 1321/2014 4.1.1 Section 1: General Diodes Introduction to Diodes Diodes are electronic devices that allow the passage of current in only one direction. The first such device was a vacuum-tube diode (valve), consisting of evacuated glass or steel envelope containing two electrodes – the anode and the cathode. Electrons flow from the cathode to the anode. Diodes most commonly used in electronic circuits today are semiconductor diodes. This module deals exclusively with semiconductor devices. Atomic Structure of Semiconductors In order to understand how a diode functions, it is necessary to describe how semiconductor materials are used. The two materials used in semiconductors are: Silicon. Germanium. The electrical properties of a semiconductor material are determined by its atomic structure. In a crystal of pure silicon or germanium, each atom in the crystal has four valence electrons in the outer shell. An atom requires eight electrons in the outer shell in order to form a stable structure. The atoms therefore have a valence of 4. The silicon and germanium crystals require 4 electrons to stabilise the structure. Each atom interacts with the electrons of neighbouring atoms and form a strong crystal lattice. This interaction between atoms gives a very stable arrangement and because the electrons are not free to move, pure silicon and germanium are very good insulators at low temperatures being a perfect insulator at absolute zero (- 273.15°C) At room temperature the atoms vibrate in the lattice causing a few bonds to break producing free valence electrons. When this happens a valence or hole is left behind, by each free electron, in the outer shell. Free electrons are attracted to the holes resulting in a neutral or stable structure again. Doping To improve conductivity of the semiconductor material, the silicon and germanium crystals are doped with impurity atoms. Such impurities function in one of two ways, donor or acceptor impurities. Initial Issue AL1 7 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Donor Impurity An impurity element such as phosphorous, antimony, or arsenic is called a donor impurity because it contributes, or donates, excess electrons. This group of elements has five valence electrons, only four of which bond with the silicon or germanium atoms. Thus, when an electric field is applied to the semiconductor, the remaining electrons are free to move through the crystalline material. This is called a negative or N-TYPE SEMICONDUCTOR Acceptor Impurity An impurity element such as gallium and indium have only three valence electrons. This is one less than is required to complete the inter-atomic bond within the crystal. Such impurities are known as acceptor impurities because these elements accept electrons from neighbouring atoms to satisfy the deficiency in the valence bond. The resultant deficiencies, or holes, are filled by other electrons and so on. These holes behave as positive charges, appearing to move under an applied voltage in a direction opposite to that of the electrons. This is called a positive or P-TYPE SEMICONDUCTOR. P-Type and N-Type Semiconductors When a single crystal containing both N-type and P-type regions is manufactured, this results in a P-N junction where the two crystals are joined. (Fig 1) P N PN Junction (Barrier Layer) FIG 1 When an external voltage is applied, the P-N junction acts as a rectifier, i.e. current can only flow in one direction. Initial Issue AL1 8 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals If the P-Type region is connected to the positive terminal of a battery and the N-Type to the negative terminal, as in Fig 2, a large current flows through the material across the junction. This is called forward bias and the voltage necessary to make the diodes conduct is called the junction voltage. It is approximately 0.2V for germanium and 0.6V for silicon type semiconductors. + - P N FIG 2 If the battery is connected in the opposite manner, as in Fig 3, then current does not flow. This is called reverse bias where the voltage increases the P-N junction or barrier layer which becomes wider. - + P N FIG 3 This type of device is called a junction diode or general purpose diode. Initial Issue AL1 9 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Majority and Minority Carriers N Type Semiconductor In a doped N Type semiconductor, the impurity atoms produce a large supply of free electrons. The electrons produce a large forward current called the majority carriers. A small current is also produced due to the movement of holes in the material. The holes produce a small reverse current called the minority carriers or leakage current. P Type Semiconductor In a doped P type semiconductor, the impurity atoms produce a large supply of free holes. The holes produce a large forward current called the majority carriers. A small current is also produced due to the movement of electrons in the material. The electrons produce a small reverse current called the minority carriers or leakage current. The majority carriers and minority carriers produce currents in opposite directions. Fig 4 shows carriers when forward biased. + - P N Majority Carriers Minority Carriers FIG 4 Initial Issue AL1 10 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Even when reverse biased, a small leakage current exists as shown in Fig 5. FIG 5 The minority carriers or leakage current in a semiconductor increases with an increase of temperature. Silicon produces significantly less leakage current than germanium. Operating conditions, such as temperature variations, often determine the selection of silicon or germanium semiconductor devices. Initial Issue AL1 11 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 2: Junction Diodes Introduction A junction diode is an extremely useful device in both digital and analogue circuits and is made from a P-N semiconductor. Symbols The diode may be drawn using the symbols shown in Fig 1. In Fig 1a a circular envelope surrounds the diode symbol. In Fig 1b the dot indicates that diode casing is connected to the cathode. The dot could also be shown at the anode. In Fig 1c and 1d, it is usual to omit the circle and only show the diode symbol. Anode Cathode Anode Cathode (a) (b) (c) (d) FIG 1 In Fig 2a the cathode is indicated on the diode components as either a black or white band. In Fig 2b on larger diodes, where there is sufficient area, a diode symbol may be printed on the casing. (a) (b) FIG 2 Initial Issue AL1 12 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Other types of diode packages are shown in Fig 3. FIG 3 Initial Issue AL1 13 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Characteristics of a Junction Diode Fig 4 shows the output characteristics of a silicon junction diode whilst Fig 5 shows the output characteristics of a germanium junction diode. Silicon Diode FIG 4 When the forward bias reaches 0.6V conduction occurs. Leakage current of about 1µA is due to minority carriers. Germanium Diode FIG 5 The same action occurs as for the silicon diode except conduction occurs at 0.2V forward bias and the leakage current is about 1mA. Initial Issue AL1 14 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Parameters There are many different types of diode produced, however, there are several parameters we must consider when selecting the correct diode to use. These parameters will be specified by the manufacturer on the component’s datasheet and include: Peak Inverse Voltage Maximum Forward Current Temperature Frequency Leakage Current Power Dissipation Peak Inverse Voltage The Peak Inverse Voltage (PIV) or Maximum Reverse Voltage is the maximum allowable operating voltage that can be applied across the diode, in reverse bias, without breakdown and damage occurring to the device. The PIV is usually less than the “avalanche breakdown” level on the reverse bias characteristic curve (refer to Fig 4 and 5 above). Typical values of PIV range from a few volts to thousands of volts depending on the diode. This must be considered and understood when replacing a diode. Generally, the PIV is larger in a silicon diode than a germanium. Maximum Forward Current As the name suggests the Maximum Forward Current is the largest current that a PN junction or diode can carry without damaging the device. The more current a diode allows to pass through it the greater the power and therefore the heat that is generated. Excessive current means too much heat leading to breakdown of the component. Temperature When we pass current through a diode it gets hot and, as suggested earlier, too much heat will cause the device to fail. An ideal diode will have zero current when off (reverse bias), and therefore the power being dissipated when not conducting will also be zero, allowing the device to cool. In reality there is leakage current when reverse biased and therefore some heat we be generated. As the leakage current doubles for every 10°C increase in temperature, a rise in temperature leads to more leakage current, potentially leading to thermal runaway. Consequently, controlling the temperature is critically important. Because of this each diode will have a Maximum Operating Temperature stated and will be typically: 150 to 200°C for a silicon diode 80 to 100°C for a germanium diode Initial Issue AL1 15 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Frequency Because a diode is constructed similar to that of a capacitor, it will exhibit what is known as Junction Capacitance. This capacitance places a limitation on the frequency under which a diode can operate for two main reasons. At low frequencies, the capacitive reactance of the device is high and will therefore have little impact on the reverse bias leakage current. However, at higher frequencies, the reactance will be low and therefore the leakage current will increase. Consequently, at too high a frequency the device will not be able to stop conducting in reverse bias. The second impact of the junction capacitance is on the switching time. Reversing the voltage will take time to achieve as a capacitor cannot change the voltage across it instantaneously. Leakage Current As stated earlier, because of minority carriers we have leakage current flowing in reverse bias which will increase with an increase in temperature. The reverse current of a silicon diode, at a given temperature, is about 1/1000th that of a similar germanium diode. As a result, as seen on the characteristic curves in Fig 4 and 5 this is a few micro-amps for silicon and milli-amps for germanium. Total Power Dissipation Signal diodes have a Total Power Dissipation rating. This rating is the maximum possible power dissipation of the diode when it is forward biased and conducting. When current flows through the diode the biasing of the PN junction is not perfect and offers some resistance to the flow of current resulting in power being dissipated in the diode in the form of heat. To find the power that will be dissipated by a diode, the volt drop across it must be multiplied by the current flowing through it. Comparison of Silicon and Germanium Diodes To summarise some of the points made above: Silicon diodes can withstand higher reverse voltages than the equivalent germanium diode before breakdown occurs. Leakage current for a silicon diode is approximately 1/1000th that of a germanium diode. A silicon diode can be used at higher temperature levels about 150 to 200°C whereas a germanium diode has an upper limit of about 80 to 100°C Analogue Circuit Configuration The following examples use silicon diodes with a forward bias of 0.6V. As it takes 0.6V to start to conduct, the diode effectively drops 0.6V across the diode. Example 1 Fig 6 shows a configuration to pass positive voltages. Initial Issue AL1 16 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Input Voltage Output Voltage 2 1.4 1 0.4 0 0 -1 0 -2 0 FIG 6 It can be seen that conduction takes place when the anode is at least 0.6V higher than the cathode. Example 2 Fig 7 shows a configuration to pass negative voltages. Input Voltage Output Voltage 2 0 1 0 0 0 -1 -0.4 -2 -1.4 FIG 7 Conduction takes place when cathode is at least 0.6V less than anode. Conclusion When the anode is at least 0.6V above the cathode, the diode is forward biased and conducts. Initial Issue AL1 17 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Example 3 Fig 8 shows positive limiting. Input Voltage Output Voltage 2 0.6 1 0.6 0 0 -1 -1 -2 -2 FIG 8 The diode conducts when the anode is at least 0.6V more than the cathode so limiting the output voltage. The maximum voltage positively is +0.6V due to the diode conducting to 0V. Example 4 Fig 9 shows negative limiting. Input Voltage Output Voltage 2 2 1 1 0 0 -1 -0.6 -2 -0.6 FIG 9 The diode conducts when the cathode is at least 0.6V less than the anode so limiting the output voltage. The maximum voltage negativity is –0.6V due to the diode conducting to 0V. Initial Issue AL1 18 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Digital Circuit Configuration Example 1 Input Voltage Output Voltage A B 0 0 0 0 5 4.4 5 0 4.4 5 5 4.4 FIG 10 Fig 10 shows a circuit that has two inputs, ‘A’ and ‘B’, from fault detection sensors. If either ‘A’ or ‘B’ or both produce an input voltage of 5V, then the alarm will sound. If the two inputs were connected directly to the alarm and ‘A’ produced a 5V output, this would send a 5V to the ‘B’ sensor and vice versa. The diodes isolate the two inputs producing an output when ‘A’ or ‘B’ senses a fault. Initial Issue AL1 19 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Test - Multimeters A diode can be tested using special diode testers or a multimeter. Many digital multimeters have a diode test facility built in, however, a diode resistance can be measured to ascertain the serviceability. Fig 11 shows one type of multimeter with the diode test mode selected. This type of multimeter also emits a tone if a short circuit is detected. FIG 11 Initial Issue AL1 20 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Test - Connections To test a diode fully, it must be tested in forward and reverse bias using the positive and common multimeter connections. Forward Bias 1. The positive is connected to the anode. 2. The common is connected to the cathode. Reverse Bias 1. The common is connected to the anode. 2. The positive is connected to the cathode. Different multimeters may display the results differently but are carrying out the same test. When testing a diode the output display is a measure of how much voltage, from the multimeter, is developed across the diode under test. The higher the resistance of the diode, the more voltage is developed across the diode, the higher the multimeter reading. The lower the resistance of the diode, the less voltage is developed across the diode, the lower the multimeter reading. On some multimeters a high reading may be displayed as a 1 on others OL for Out Limits. A low reading is generally between 0.5 and 0.9V dependent upon the diode under test. NOTE: Care must be taken to ensure that you are not in contact with the diode connections during a test. The reading will be affected by the resistance of the body making a parallel circuit with the diode. Initial Issue AL1 21 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Test – Serviceable Diode Fig 12 shows a serviceable diode under test when forward biased. FIG 12 The reading is 00.6 indicating a low reading. Initial Issue AL1 22 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Fig 13 shows a serviceable diode under test when reverse biased. FIG 13 The reading is OL indicating a high reading. Any reading other than low for forward biased and high for reverse biased indicates an unserviceable diode. A diode may be damaged due to excessive currents or voltages that breaks down the P-N material of the diode. Initial Issue AL1 23 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Test – Open Circuit Diode If a diode is open circuit it has an extremely high resistance value. All the supplied voltage for the test is developed across the diode in both forward and reverse biasing. This produces high readings for forward and reverse bias. Fig 14 shows an open circuit diode under test. FIG 14 Initial Issue AL1 24 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Test – Short Circuit Diode If a diode is short circuit, it has an extremely low resistance value. Only a small amount of the supply voltage is developed across the diode in both forward and reverse bias. This produces a low reading for forward and reverse bias. Fig 15 shows a short circuit diode under test. FIG 15 Initial Issue AL1 25 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diode Test – Resistive Diode A diode may become resistive where it is somewhere between open and short circuit. The resistance of the diode will be the same for forward and reverse biases giving a reading between low and high. Fig 16 shows a resistive diode under test. FIG 16 Diode Test - Consolidation Fig 17 shows a table of expected readings for different serviceability states of a diode. READINGS State Forward Bias Reverse Bias Serviceable LOW HIGH Open Circuit HIGH HIGH Short Circuit LOW LOW Resistive Between LOW and HIGH FIG 17 Initial Issue AL1 26 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 3: Rectifier Diode Introduction The function of rectifier diodes is to convert an alternating current (ac) to a dc output. Half-Wave Rectification Using one diode gives half-wave rectification as shown in Fig 1. FIG 1 Only the positive half cycles are allowed through the rectifier diode, the negative cycles are blocked. By adding a capacitor to the output, the positive half cycles charges up the capacitor to produce a dc voltage as shown in Fig 2. FIG 2 Initial Issue AL1 27 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Full-Wave Rectification To achieve full wave rectification of an ac input, four diodes are used as a bridge rectifier. The bridge rectifier is often housed in a single component. Fig 3 shows a typical schematic of a bridge rectifier. FIG 3 Action: Positive Half Cycle As the input signal is on the positive half cycle a positive is seen at the junction between ‘D1’ and ‘D2’, whilst a negative is seen at the junction between ‘D3’ and ‘D4’. Therefore: Because of the positive on the junction of ‘D1’ and ‘D2’, D1’s cathode is more positive than the anode and therefore is reversed biased and is OFF D2’s anode is more positive than the cathode so is forward biased and is ON Because of the negative on the junction of ‘D3’ and ‘D4’, D3’s cathode is more negative than the anode and therefore is forward biased and is ON D4’s anode is more negative than the cathode so is reverse biased and is OFF Conventional current is then allowed to flow DOWN through RL developing a positive half cycle across the load. Negative Half Cycle During the negative half cycle the opposite is true. A negative is seen at the junction between ‘D1’ and ‘D2’, whilst a positive is seen at the junction between ‘D3’ and ‘D4’. Therefore: Because of the negative on the junction of ‘D1’ and ‘D2’, Initial Issue AL1 28 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals D1’s cathode is more negative than the anode and therefore is forward biased and is ON D2’s anode is more negative than the cathode so is reverse biased and is OFF Because of the positive on the junction of ‘D3’ and ‘D4’, D3’s cathode is more positive than the anode and therefore is reversed biased and is OFF D4’s anode is more positive than the cathode so is forward biased and is ON This ensures that conventional current is still flowing DOWN through RL and therefore still developing a positive half cycle across the load. So both half cycles will allow current to only flow in one direction through the load, converting the ac into dc. The output then goes to smoothing circuits to remove any ripple present. Initial Issue AL1 29 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diodes in Series Rectifier diodes may be used for HIGH VOLTAGE RECTIFICATION where the reverse bias exceeds the level that would damage it. To overcome this, rectifier diodes are placed in series to equally share the high REVERSE VOLTAGE. High value resistors (about 100KΩ) are placed in parallel to the diodes to swamp any differences in diode reverse resistance. This is typically between 1 and 10 MΩ for a silicon rectifier diode. Fig 4 shows a typical layout. FIG 4 When the diodes are forward biased, the overall parallel resistance is low, as the high value resistors have little effect on the circuit. When the diodes are reverse biased, the high resistance of a diode is in parallel with the high value resistor producing a resultant resistance in which the high voltage is shared between the 3 circuits in series. Initial Issue AL1 30 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Diodes in Parallel Several rectifier diodes may be used where there is a large output current required that may damage a single diode. Rectifier diodes are placed in parallel to equally share the forward currents. In order to ensure that all the diodes equally share the forward current, low value resistors are placed in series with the diode to swamp any differences in the forward resistance of each diode. Fig 5 shows a typical layout. FIG 5 Initial Issue AL1 31 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 4: The Varistor Introduction The varistor is a semiconductor device used for reducing or clipping noise spikes from ac and dc voltages. Heavy duty motors and relays can generate very large voltage spikes which interfere with power supplies. The noise spikes have such a short duration and large amplitude that they can be difficult to filter out. In rectification circuits these noise spikes can be superimposed upon the dc regulated output voltage which is an undesirable condition. The solution is to attenuate the high frequency spikes before the ac is rectified by using a varistor device. Symbol The symbol for a varistor is shown at Fig 1. FIG 1 Characteristics of a Varistor The metal oxide varistor (MOV), is a semiconductor resistor made of zinc oxide semiconductor crystals. When the voltage across this resistor reaches a breakdown voltage, it changes from being a resistor to a very good conductor. It performs like a switch that has a positive and negative switching voltage preset. Fig 2 shows how a varistor set at positive 200V and negative 200V and switches extremely fast. -200 v +200 v 0 FIG 2 Initial Issue AL1 32 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Circuit Configuration Fig 3 shows a typical circuit layout with the varistor placed before rectification takes place. FIG 3 The input ac voltage has noise spikes superimposed upon it as shown by Fig 4. These noise spikes are random and of different amplitudes. FIG 4 The varistor has a breakdown voltage that is sufficiently higher than the ac voltage to make sure that the signal is not clipped, only the noise is reduced. Initial Issue AL1 33 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Fig 5 indicates the breakdown voltage level of the varistor. FIG 5 The resultant ac voltage for rectification is shown in Fig 6. The noise spikes have been reduced and are easier to eliminate or filter during rectification. FIG 6 Initial Issue AL1 34 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 5: Silicon Controlled Rectifier Introduction The Silicon Controlled Rectifier (SCR), also called a Thyristor, is a current controlled semiconductor device that has three terminals: Anode. Cathode. Gate. The gate is used to control or switch on the diode when required and allow current to flow through the device. This is achieved by a current pulse to the gate, and may be positive or negative depending upon the type of SCR. P-Gate SCR The symbol for a P-Gate SCR is shown at Fig 1. FIG 1 In a P-Gate or cathode controlled SCR, the gate requires a positive current to switch it on. Without the trigger, the diode is off and no current can flow. If the anode is more positive than the cathode and a POSITIVE CURRENT, sufficient to trigger the gate, is applied, then current will flow through the SCR. The SCR will continue to conduct, even after the gate current has been removed. The SCR will switch off only when the current flowing through the device drops below a specific level called the HOLDING CURRENT. Initial Issue AL1 35 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals N-Gate SCR The symbol for a N-Gate SCR is shown at Fig 2. FIG 2 In a N-Gate or anode controlled SCR, the gate requires a negative current to switch it on. Without the trigger, the diode is off and no current can flow. If the anode is more positive than the cathode and a NEGATIVE CURRENT, sufficient to trigger the gate, is applied, then current will flow through the SCR. As in the P-Gate SCR, the SCR will continue to conduct, even after the gate current has been removed and will switch off when the holding current drops below a specific level. Initial Issue AL1 36 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Circuit Application Fig 3 shows an example of a SCR used to light a lamp. The switch ‘SW1’ allows voltage to be applied to the circuit. The push switch ‘SW2’ allows when operated, a positive voltage to be applied to the gate of the SCR. The SCR is a P-Gate cathode controlled device requiring a positive input. The lamp indicates if the SCR is conducting by providing current through the lamp. FIG 3 With the switch open no voltage is applied to the SCR, therefore there is no current around the circuit and the lamp is off. When the switch ‘SW1’ is closed: 6V is applied to the anode of the SCR. When the switch ‘SW2’ is pressed (closed): The positive voltage through ‘SW2’ puts a positive voltage to the gate of the SCR. The SCR is triggered into conduction allowing current to flow through to the lamp. The lamp lights. When ‘SW2’ is released (open) The SCR continues to conduct. When the switch ‘SW1’ is opened again: The supply voltage is removed from the anode of the SCR. The current through the SCR drops below the holding current. The SCR switches off. The lamp goes off. Initial Issue AL1 37 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Overall View The SCR conducts when the anode is more positive than the cathode and is triggered dependent upon the type of SCR. It will continue to conduct, even after the gate current has been removed, until the current drops low enough to stop conduction. This is where the term controlled rectifier comes from. A second method of conduction is where the anode voltage increases high enough above the cathode voltage to make the SCR break down into conduction. This is known as the breakover voltage and may damage the device The SCR has many advantages over mechanical switching devices such as: No moving parts No contact arcing on switching No poor contacts due to corrosion or dust Usually smaller than an equivalent mechanical device Consumes less energy for switching Initial Issue AL1 38 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 6: Light Emitting Diodes Introduction A Light Emitting Diode (LED) is a semiconductor device that gives out light when forward biased and a small current of around 10 to 30 mA flows through it. LEDs are used extensively as electronic indicators. They are available in a range of sizes and shapes and a variety of colours. Symbol of a Basic LED The symbol for a basic LED is shown in Fig 1. FIG 1 What is Light? Light is a form of energy. The most basic unit of light is a particle known as a photon. Photons do not have mass; however, they do contain energy and momentum. How are Photons Produced? We understand that electrons move in shells orbiting around the nucleus. Electrons in different shells have differing energies dependent on their distance from the nucleus and generally speaking, electrons with greater energy orbit farther away from the nucleus. Therefore, for an electron to move or from an inner to an outer orbit, or indeed break orbit to become a free electron, it must gain energy. Moving the other way it must release energy. This release of energy is the photon and is created when a free electron fills a hole and joins an orbit. For an electron to jump from a lower orbital to a higher orbital, something has to boost its energy level. Conversely, an electron releases energy when it drops from a higher orbital to a lower one. This energy is released in the form of a photon. Indeed a greater energy drop releases a higher-energy photon, which is characterized by a higher frequency of light. By considering the E-M spectrum (covered in the physics module) then differing frequencies means differing colour of light produced. This phenomenon happens in any diode, but you can only see the photons when the diode is composed of certain material. For example, the atoms in a normal P-N junction diode made of silicon are arranged in such a way that the electron drops a Initial Issue AL1 39 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals relatively short distance. As a result, the photon's frequency is so low that it is invisible to the human eye - it is in the infrared portion of the light spectrum. LED Construction LEDs however are made of materials that have a wider gap between where the electrons can break free (the outer shell) and the inner shell. One example is gallium arsenide phosphide. The size of the gap determines the frequency of the photon and therefore the colour of the light produced. FIG 1 - INSIDE A LIGHT EMITTING DIODE In terms of light emission ordinary PN diodes are very inefficient and most of the released energy is absorbed in the diode itself in the form of heat. LEDs however are specially constructed to release a large number of photons outward. Additionally, they are housed in a plastic bulb that concentrates the light in a particular direction. As you can see in Fig 2, most of the light from the diode bounces off the sides of the bulb, travelling on through the rounded end. LEDs can be damaged by too high a reverse voltage. A reverse voltage of 5V is sufficient to damage an LED. Different shapes and sizes of LED can be manufactured by adjusting the lens construction. There are 2 ways to determine which lead on an LED is anode and cathode, they are: The cathode lead is shorter than the anode lead. The case of the LED may have a flat side by the cathode. Initial Issue AL1 40 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals LED Bias Voltages Basic LEDs are available in a variety of colours. Fig 3 gives examples of the forward bias voltage required for each type of LED with the current limited to 20mA. INFRA- RED ORANGE YELLOW GREEN BLUE WHITE RED 1.7V 2V 2V 2.1V 2.2V 3.3V 3.4V FIG 3 Viewing Angle Basic LEDs are available in a variety of output brightness, measured in millicandelas (mCd). The type of LED also determines the viewing angle of the output light. Fig 4 shows the output viewing angle of an LED. FIG 4 Fig 5 shows typical output viewing angles for different types of LEDs, the angles will vary with application required. The brighter LEDs have the light output concentrated into a narrower beam. HIGH SUPER ULTRA HYPER TYPE STANDARD BRIGHTNESS BRIGHT BRIGHT BRIGHT Viewing 60° 40° 30° 25° 25° angle FIG 5 Initial Issue AL1 41 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Circuit Application Fig 3 showed the different operating voltages dependent upon the type of LED. A practical circuit must have a resistor included to drop the supply voltage to the required level. Fig 6 shows a simple circuit. FIG 6 Vs is the supply voltage Vf is the diode voltage If is the supply current The LED requires 2V supply R is required to drop the supply voltage leaving 2V for the LED To supply the LED with the required voltage, all except 2V needs to be dropped V Vs − Vf across R. By Ohms Law R = so R = I If Initial Issue AL1 42 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Example If Vs = 9V Vf = 2V 9−2 If = 10mA then = 700Ω 10 ×10 −3 The LED must be connected so that it is forward biased, which means the anode is positive with respect to the cathode. Fig 7 shows the LED is forward biased with a switched positive supply voltage. 700Ω FIG 7 Fig 8 shows the LED forward biased with a switched zero volts supply voltage. FIG 8 Initial Issue AL1 43 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Bi-Colour LED LEDs are also available where the single package can produce two different colours dependent upon how the LED is connected. It can be used for a GO/NO-GO indicator. Fig 9 shows the connections to the LED. FIG 9 If a positive voltage, with respect to B, is applied to A, then the green LED illuminates. If a positive voltage, with respect to A, is applied to B then the red LED illuminates. If there is no forward bias then the LEDs are off. Initial Issue AL1 44 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Multicolour LED LEDs are also available where a single package can produce 3 different colours. Fig 10 shows the connections to the LED. FIG 10 With the cathode at zero volts and If anode 1 has a positive voltage then the green LED illuminates If anode 2 has a positive voltage then the red LED illuminates If both anode 1 and anode 2 have positive voltages applied then both the green and red LEDs illuminate producing yellow. An example of usage in a circuit is where: Green for good. Yellow for a warning. Red for failure. Initial Issue AL1 45 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals 7 Segment LED Display LEDs are also constructed for specific uses as in a 7 segment display. The display consists of seven LEDs arranged in a figure of eight as in Fig 11. This allows numbers from 0 to 9 to be displayed by switching on a combination of segments a to g. a a b c b f g d e f g c e d Cathode FIG 11 In a COMMON CATHODE 7 segment display, all seven LEDs have their cathodes connected together internally. Applying a positive voltage to each segment lights the appropriate LED. Example 1 If the cathode is connected to zero volts and a positive voltage to segments a, c, d, f and g, then the number 2 is displayed. In a COMMON ANODE 7 segment display, all seven LEDs have their anodes connected together internally. With the anode at a positive voltage then a zero volts on each segment lights the appropriate LED. Example 2 With the anode connected to 2V and zero volts to segments b, e, f and g, then the number 4 is displayed A test to ensure all the LEDs in the display are working is to illuminate all the segments at once, displaying the number 8. Initial Issue AL1 46 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Multisegment LED Displays In order to display letters as well as numbers, the amount of LEDs on displays can be increased, the figure below shows the layouts of some multi-segment LED displays. The segments are lit by the same principle as the 7 segment display. FIG 12 Example To display the letter A in a 14 segment display, the segments in Fig 13 are illuminated. FIG 13 Advantages of LEDs LEDs have several advantages over conventional incandescent lamps: They don't have a filament that will burn out, so they last much longer. The plastic bulb makes them a lot more durable. They are mountable on PCB’s and therefore fit more easily into modern electronic circuits. They are very efficient - Incandescent bulbs give out significant amounts of heat. Initial Issue AL1 47 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Technology Up until recently, LEDs were too expensive to use for most lighting applications because they're built around advanced semiconductor material. However as the price of semiconductors has fallen significantly LEDs are used in more and more applications. Christmas tree lights, Torch bulbs, car side and brake lights are just a few examples that have transferred to LEDs in the last few years. Initial Issue AL1 48 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 7: Photo Conductive Diode Introduction The structure of a photo conductive diode is similar to a normal junction diode except the junction is exposed via a transparent window. Photo diodes are operated in REVERSE BIAS and the minority current (leakage current) increases in direct proportion to the light intensity applied to the PN junction. The light illuminates the PN junction causing the bonds holding the crystal lattice to break down producing current flow. Symbol for Photo Diode The symbol for a photo diode is shown at Fig 1. FIG 1 Construction Photo diodes are normally constructed of silicon with the top of the package having a see-through window. The maximum response is in the infra-red region of light. The current produced is very small and needs to be amplified before use. Application Photo diodes are used in various ways such as: Sensing when a beam of light is interrupted, for example: o Smoke detector. o Camera trigger. o Alarm systems. Sensing the ambient light level, for example: o Automatic control of cockpit lighting. Sensing levels of fluid in a container. Initial Issue AL1 49 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Chapter 2: Transistors EASA 2023/989 4.1.2 CAA 1321/2014 4.1.2 Section 1: Bi-Polar Transistor Introduction to Transistors The transistor was invented in 1948 at Bell Laboratories in America and revolutionised electronic design. Transistors are utilised inside many electronic devices such as computers, audio and video equipment and communication system. Its name is derived from ‘trans resistor’ meaning that it can transfer its internal resistance from low ‘R’ in the base/emitter circuit to a much higher ‘R’ in the collector base circuit. Symbol for an NPN Transistor Fig 1 shows the symbol for an NPN transistor. FIG 1 The arrow points outwards for a P type base. NPN Transistor Construction The NPN transistor consists of a very thin layer of P-type material between 2 sections of N-type material arranged as shown in Fig 2. N Collector P Base N Emitter Initial Issue AL1 50 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals FIG 2 Initial Issue AL1 51 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals NPN Transistor Operation To permit the forward flow of current across the PN junction, between base and emitter, the base must be more POSITIVE than the emitter. (as in a diode, about 0.6v). The N-type material in the output circuit serves as the collector element, which has a large positive voltage with respect to the base, to prevent reverse current flow. Electrons moving from the emitter to the base, are attracted to the positively charged collector and flow through the output circuit. The input impedance, or resistance to current flow, between the base and emitter is low, whereas the output impedance between collector and base is high. Therefore, small changes in the voltage applied to the base causes large changes in the voltage drop across the collector resistance, making this type of transistor an effective current amplifier. NPN Transistor Switching Action When used as a switch, the transistor conducts into saturation. If the base is more positive than the emitter by 0.6V or greater then the transistor is ON This causes the collector to connect internally to the emitter (like closing a switch) If the base/emitter is reverse biased then the transistor is OFF. The collector/emitter is open circuit. (like opening a switch) Figs 3 and 4 show typical transistor switching circuit layouts. Input Output Transistor Voltage Voltage State 2 0 On 1 0 On 0 9 Off -1 9 Off -2 9 Off FIG 3 With an input below 0.6V, reverse biasing the base/emitter junction, the output is 9V (collector voltage). With an input above 0.6V, forward biasing the base/emitter junction, the output is 0V (emitter voltage) because 9 volts is developed across the load resistor. Initial Issue AL1 52 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals With a square wave input to the transistor, as in Fig 4, a square wave is produced on the output, switching between the supply voltage and the emitter voltage. The output is antiphase to the input. FIG 4 NPN Transistor Amplifier Action When used as a SWITCH the transistor conducts to SATURATION. When used as an amplifier the circuit is constructed to ensure that the transistor does not saturate as distortion may occur to the output signal. An amplifier produces an output greater than the input. The gain of an amplifier is calculated as the ratio of change of output current to change of input current. Current Gain = Change of Output Current ∆Ι C Change of Input Current = ∆Ι B ∆Ι C = 4mA Example ∆Ι B = 20 µA 4 × 10 −3 gain = = 200 20 × 10 − 6 Initial Issue AL1 53 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Example Fig 5 shows an input signal of 1mV peak to peak on the input. (Additional circuitry not shown). FIG 5 With a gain of 200, the output is 200 x 1mV = 200mV The output is antiphase to the input. An amplifier can be used to amplify ac or dc signals. Initial Issue AL1 54 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Symbol for a PNP Transistor Fig 6 shows the symbol for a PNP transistor. FIG 6 The arrow points in for an N Type base. PNP Transistor Construction The PNP transistor consists of a very thin layer of N-Type material between 2 sections of P-type material arranged as shown in Fig 7. P Collector N Base P Emitter FIG 7 Initial Issue AL1 55 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals To permit the forward flow of current across the PN junction, between base and emitter, the base must be more negative than the emitter (as in a diode, about 0.6V). The P-Type material in the output circuit serves as the collector element. As in the NPN transistor small changes in voltage on the base cause large changes in the voltage drop across the collector resistance. PNP Transistor Switching Action When the base is more negative than the emitter by 0.6V – The transistor is ON. This causes the collector to connect to the emitter voltage (like closing a switch) If the base/emitter is reverse biased the transistor is OFF and the emitter/collector is open circuit Figs 8 and 9 shows a typical layout of a transistor switching circuit. Input Output Transistor Voltage Voltage State 9 0 Off 8.5 0 Off 8 9 On 7.5 9 On FIG 8 If the emitter voltage is less than 0.6V above the input voltage, the base/emitter junction is reverse biased and the output is at the collection voltage (OV). If the emitter voltage is more than 0.6V above the input voltage, the base/emitter junction is forward biased and the output is at the emitter voltage (9V). Initial Issue AL1 56 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals In Fig 9, the input square wave switches the output between 0V and 9V in antiphase to the input FIG 9 PNP Transistor Amplifier Action A PNP transistor amplifier gain is calculated in the same way as the NPN transistor amplifier. The output is also antiphase to the input as shown in Fig 1. FIG 10 Initial Issue AL1 57 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 2: Field Effect Transistors (FET) A field effect transistor (FET) is a unipolar device. This means that it will conduct a current using only one kind of charge carrier. If based on an N-type bar of semiconductor the carriers are electrons and a P-type device uses only holes. Junction Gate FET The Junction Gate Field Effect Transistor is abbreviated to either JUGFET or JFET and in its basic form is a bar of silicon whose conducting properties are controlled by the depletion layer of a reverse biased P-N junction. These devices have three terminals named SOURCE, DRAIN and GATE that can be compared to the EMITTER, COLLECTOR and BASE of a BJT. The bar of semiconductor forms a conducting channel between the SOURCE and the DRAIN connections. The resistance of this channel can be controlled from very low resistance (short circuit) to very high resistance (open circuit) by applying a relatively small voltage to the GATE connection. In an N-channel device, a P-type region near the centre of the bar serves as a control electrode, the gate. Symbol for an N-Type JUGFET The symbol for an N-Type JFET is shown at Fig 1, Note the arrow points in towards the N-Type material. FIG 1 Initial Issue AL1 58 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals JFET Operation FIG 2 A properly biased N-channel JFET is shown in Figure 2. The gate forms a diode junction to the source and is reverse biased. If a voltage (or an ohmmeter) were applied between the source and drain the N-type bar would conduct in either direction because of the doping. No gate bias is required for conduction. If a gate junction is formed as shown, conduction can be controlled by the degree of reverse bias voltage VGS. As the level of reverse bias is increased (Figure 3) the depletion layer widens between the gate and the source and effectively increases the resistance between the source and the drain. This reverse bias voltage on the gate may be increased to a point that completely blocks the flow of current between the source and the drain. This point is known as ‘pinch off’. FIG 3: DEPLETION LAYER INCREASING WITH INCREASED VGS N-channel JFET: (a) Narrow depletion layer at gate. (b) Reverse biased gate increases depletion region. (c) Increasing reverse bias enlarges depletion region. (d) Increasing reverse bias pinches-off the Source-to-Drain channel. Initial Issue AL1 59 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Key Points: The unipolar junction field effect transistor (FET or JFET) is so called because conduction in the channel is due to one type of carrier The JFET source, gate, and drain correspond to the BJT's emitter, base, and collector, respectively. Application of reverse bias to the gate varies the channel resistance by expanding the gate depletion region. The value of VGS that causes current ID to cease is known as ‘pinch-off’. Bipolar Junction Field Effect Transistor Transistor (BJT) (FET) Connections Emitter, Base, Collector Source, Gate, Drain Normal OFF (not conducting) ON (conducting) Condition Voltage VGS Control Current IBE (Forward Bias) (Reverse Bias) Initial Issue AL1 60 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 3: Photo Transistor Introduction A photo transistor is a P-N junction device that is constructed in a similar manner to an ordinary bi-polar transistor. It is used in a similar manner to the photo diode however due to the transistors ability to amplify there is a substantial increase in output current produced. It is constructed like a photo diode with a window to allow lights in but has 3 legs, instead of only 2 as in a photo diode. Symbol for a Photo Transistor Fig 1 shows the symbol for an NPN Photo-Transistor. FIG 1 Construction The photo-transistor has a base, emitter and collector connections but the base is only used in a few applications. The base can be used to bias the transistor to set the switch on operating point. Photo Transistor Operation The output current of the photo transistor is controlled by the intensity of light striking the photo transistor through the device’s window. The greater the light, the more the transistor switches on the current to the collector. Photo Transistor Details The differences between a Photo Transistor and a Photo Diode are: The Photo-Transistor can produce a much higher output for the same amount of light intensity. The Photo Transistor has a higher sensitivity for use over a wider range of applications. The Photo Diode responds faster to changes in light intensity and is more suitable for fast switching applications. Photo Transistor Uses Often used in applications such as, Tachometers, Photographic exposure controls, Smoke detectors and Positional adjustments of objects. Initial Issue AL1 61 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Chapter 3: Integrated Circuits EASA 2023/989 4.1.3 CAA 1321/2014 4.1.3 Section 1: Integrated Circuit Devices Specifications Introduction The integrated circuit (IC) is actually a group of extremely small solid-state components which have been formed within or on a piece of semiconductor material and then appropriately interconnected to form a complete circuit. The IC is therefore a solid-state circuit and not an individual solid-state component like a diode or a transistor. Integrated circuits are constructed in basically four different ways: Monolithic. Thin-film. Thick-film. Hybrid. ICs may also be divided into 2 major groups according to their mode of operation: Linear. Digital. The Importance of ICs Since its creation in the late 1950s, the integrated circuit has had a tremendous effect on the electronics’ industry. Before the IC was developed, all electronic circuits were constructed with individual (discrete) components which were wired together. The early vacuum tube circuits (fig 1) were quite large for the simple functions that they performed and the newer transistorised circuits, although quite small and highly efficient by comparison, still did not offer the ultimate solution. It was the integrated circuit that finally made it possible to construct extremely small but highly efficient electronic circuits. FIG 1 The integrated circuit offered in a single package, often no larger than a conventional bipolar transistor, is a complete electronic circuit consisting of Diodes, Transistors, Resistors, and Capacitors. Initial Issue AL1 62 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals The IC was produced with basically the same technology that had produced the transistor and other types of solid-state components. The same basic materials and techniques that are used to construct a bipolar transistor are used to construct an integrated circuit. Initial Issue AL1 63 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Size The small size of the integrated circuit is its most apparent advantage. A typical IC can be constructed on a piece of semiconductor material that is less than one tenth of an inch square (1/10 in2). The first standard IC package was approximately one quarter of an inch (1/4 in) long and one eighth (1/8 in) wide. However, it later became apparent that, in most applications, this package was smaller than was actually necessary because the final size of the equipment was often dictated by other components which were much larger. Therefore, the ICs that are used today come in packages that are somewhat larger than the first ones that were developed. Fig 2 shows a standard 14 pin IC. FIG 2 Fig 3 shows a package with a monolithic chip connected internally. FIG 3 Integrated circuits have been used extensively in the aerospace industry to reduce the size and weight of equipment, and complex computer systems. In most applications where size and weight must be reduced to an absolute minimum, the IC can make a significant contribution. Initial Issue AL1 64 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals The smaller circuits consume less power than conventional circuits and they cost less to operate. They generate less heat and therefore generally do not require elaborate cooling or ventilation systems. The smaller circuits are also capable of operating at higher speeds because it takes less time for signals to travel through them. This is an important consideration in the digital field where thousands of decision-making circuits are used to provide rapid solutions to various types of problems. Reliability The integrated circuit is also more reliable than a conventional circuit that is formed with discrete components. This greater reliability results because the component within the IC is a solid-state device and these components are permanently connected together with thin layers of metal. They are not soldered together like the components and faults are less likely to occur. Testing Integrated circuits are also thoroughly tested after they are assembled and only those devices which meet the required specifications are considered suitable for either military and space or industrial and commercial applications. This extensive testing of ICs, combined with the construction techniques previously described, produces a device that is highly reliable. In fact, when the IC is compared with conventional circuitry, it is often found to be thirty or even fifty times more reliable. This high degree of reliability has made the IC an important component for use in aerospace equipment and in complex digital computer systems. In each of these applications, a tremendous amount of circuitry is used and this circuitry must be reliable, as a highly complex digital computer can be rendered inoperative if just one component fails to operate properly. Cost The use of integrated circuits can also result in a substantial cost savings. When ICs are manufactured in large quantities, they can often be sold at prices which are well below those of conventional circuits. Manufacturers of ICs usually offer a standard line of devices which are produced in large quantities. If designers can utilise those standard ICs in their equipment and if they purchase them in large quantities, they can often save a considerable amount of money. However, there are situations where the cost of an integrated circuit can be higher than that of a conventional circuit. This can occur when the designer needs a special purpose IC or one that is specially constructed by the IC manufacturer to suit the needs of the designer. Under these conditions, the cost might be prohibitive, especially when only a few ICs are purchased. Any equipment which utilises ICs, instead of conventional circuitry, will have a fewer number of parts which must be assembled. Therefore, less wiring is required and less time is needed to assemble the equipment. This can mean a considerable cost reduction when a large number of units are to be produced. Also, the equipment manufacturer only has to procure and stock a relatively small number of ICs as compared to the relatively large inventory of discrete components that would be required if conventional circuitry was used. Initial Issue AL1 65 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Limitations Integrated circuits have certain limitations which make them unsuitable for certain applications, the IC is an extremely small device, it cannot handle large currents or voltages. High currents generate heat within the device and the tiny components can be easily damaged if the heat becomes excessive. High voltages can break down the insulation between the components in the IC because the components in the IC are very close together. This can result in shorts between adjacent components, which would make the IC completely useless. Therefore, most ICs are low power devices, which have low voltages (5 to 20 volts). Also, most ICs have power dissipation ratings of less than 1 watt. Components There are only four types of component constructed within an IC. Diodes and Transistors are the easiest to construct using P and N Type semiconductor material. Resistors occupy more space as the resistor value increases. Diodes and transistors are often used to produce resistor values using the resistive properties of the barrier layers. Capacitors occupy even more space. Only small values of capacitance are constructed within an IC. It is normal to use discrete capacitors external to the IC to save space. Fault Finding Integrated circuits cannot be repaired because their internal components cannot be separated. When one internal component becomes defective the whole IC becomes defective and must be replaced. Although this means that good components must be thrown away with the bad, however, this disadvantage is not as bad as it might first appear because it is offset by other factors which tend to compensate. First of all, the task of locating trouble within a system is simplified because it is only necessary to trace the problem to a specific circuit instead of an individual component. This greatly simplifies the task of maintaining highly complex systems and reduces the demands that are placed on the maintenance personnel. Also, it is possible to reduce the time required to repair the equipment and the spare parts inventory can usually be smaller. Initial Issue AL1 66 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Conclusion When all the factors are considered, the disadvantages associated with the use of integrated circuits are outweighed by their advantages. ICs are making it possible to reduce the size, weight, and cost of electronic equipment but at the same time increase its reliability. As manufacturing techniques improve, ICs are becoming more sophisticated and are capable of performing a wider range of functions in the aerospace and commercial industries. Initial Issue AL1 67 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Section 2: Integrated Circuit Construction Introduction There are 4 basic types of integrated circuits. They are classified as: Monolithic Thin-film Thick-film Hybrid Devices Each type has certain advantages over the others and also certain limitations. Monolithic ICs A Monolithic IC is constructed in basically the same way as a bipolar transistor, although the process’s requires additional steps due to the complexity of the IC. The fabrication of the IC begins with a very thin wafer of semiconductor material (usually silicon). This wafer serves as a base on which the tiny integrated circuits are formed and is commonly referred to as a Substrate. A single monolithic IC is never constructed alone, many ICs are formed on the substrate and cut to produce ‘chips’. Fig 1 shows a wafer with many monolithic ICs formed on the substrate and ready to be sliced into individual ICs. FIG 1 Initial Issue AL1 68 Oct 2024 © Air Service Training (Engineering) Limited Part 66–B04 Basic Electronics Fundamentals Fi

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