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Part I – Electronics – Unit Unit 1: Power supplies Diodes have many uses in electronics Perhaps their most obvious use is in the area of power supplies Power uses diodes as rectifies, to convert alternating current to direct current They also use diodes as regulators, to stabilize voltage This chapter covers the circuits which use diodes in these ways Power supplies also rely on other components that you have already studied Most electronic circuits use a great variety of devices It is very important to understand how they can perform together as a system As you can begin to understand how systems such as power supplies work in electronics, you can begin to understand the principles of troubleshooting Troubleshooting is an analytical process by which you can determine the cause of circuit problems It is much easier to repair circuits when you know how and why they work THE POWER SUPPLY This chapter marks your beginning study of electronic circuits The power supply is the most fundamental circuit of any electronic system The power supply changes the available electric energy (usually ac) to the form required by the various circuits cannot function One of the first steps in troubleshooting any electronic device is to check the supply voltages at various stages in the circuitry Power supplies can be very simple or very complicated depending on the requirements of the system A simple power supply may be required to furnish 12 V dc A more complicated power supply may provide several voltages, some positive and some negative with respect to the chassis ground Some power supply may have a wide tolerance regarding voltage The actual voltage output may vary ± 20 percent Another power supply may have to keep its output voltage within ± 0.01 percent Obviously, the strict tolerance complicates the design of the supply Figure 5-1 (4-1) shows a power supply as part of an electronic system Drawings of this type are called block diagrams Block diagrams are very useful for showing the various major circuits within electronic systems The power supply in Fig 5-1 (4-1) occupies one of the blocks within the system It is the most critical since it energizes the rest of the system For example, if a problem develops in the power supply, the fuse might “blow” (open) In that case, none of the voltages could be supplied to the other circuits Another type of the problem might involve the loss of only one of the outputs of the power supply Suppose the +12V dc out drops to zero because of a component failure in the power supply Circuits A and circuits B would no longer work Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit The second output of the power supply shown in Fig 5-1 (4-1) develops both positive and negative dc voltages with respects to the common point (usually the metal chassis) This out put could fail, too It is also possible that only the negative output could fail In either case, circuit C would not work normally under such conditions Troubleshooting electronic system can be made much easier with block diagrams If the symptoms indicate the failure of one of the block, the technician can devote most attention to that part of the circuit Since the power supply energizes most or all the other blocks, it is one of the first things to check when troubleshooting SELF TEST Complete the missing word in each statement Power supply will usually change ac to Power supply voltages are usually specified by using the chassis as a reference Drawings such as Fig are called diagrams On the block diagram, the circuit that energizes most or all the other blocks is called the RECTIFICATION Most electronic circuits need dc AC is supply by the power companies The purpose of the power supply is to change ac to dc rectification Alternating current flows in both directions, and direct current is only one direction Since diodes will conduct in only one direction, they are good rectifies Typical ac voltages supplied by the power companies to residential and small commercial customers are 11V, 120V, 208V and 240V Electronic circuits often require much lower voltages Transformers are used to step down the voltage to the level needed Fig 1-2 could be an electronic circuit, a battery being charged, or some other device In this chapter, the power supply circuits will be shown with load resistors (RL) The transformer in Fig 1-2 has a voltage ratio of 10:1 With 120V across the primary, 12V ac is developed across the secondary If it were not for the diode, there would be 12V ac across the load resistor The diode will allow the current to flow through the load only in the direction of the arrow Since current is flowing in only one direction, it can be called direct current When direct current flows through a load, a dc voltage appears across the load Note the polarity across the load in Fig 1-2 Electrons always move from negative to positive through a load The positive end of the load is connected to the cathode end of the rectifier In any rectified circuit, the positive end of the load will be that end which contacts the cathode of the rectifier It can also be stated Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit that the negative end of the load will be in contact with the anode of the rectifier Fig 1-3 shows the negative side of a load resister connected to the anode end of the resister It was stated that to forward bias a diode, the anode must be made positive with respect to the cathode It was also note that diode manufactures often mark the cathode with a plus (+) sign This may seem confusing When the diode acts as a rectifier, the function of the plus sign becomes clear The plus sign is placed on the cathode end to show the technician which end of the load will be positive Look at Fig 1-2 to see if this so Fig 1-4(a) shows the input waveform to the rectifier circuits of Figs 1-2 and 1-3 Two complete cycles are shown In Fig 1-4(b) the waveform that appears across the load resistor of Fig 1-2 is shown The negative half of the cycle is missing since the diode blocks it This waveform is called half-wave, pulsating dc It represents only the positive half of the ac input to the rectifier In Fig 1-3 the diode has been reversed This caused the positive half of the cycle to be blocked Fig 1-4(c) The waveform is also half-wave, pulsating dc Both circuits, Figs 1-2 and 1-3 are classified as half-wave rectifiers The ground reference point will determine which way the waveform will be shown for a rectifier circuit For example, in Fig 1-3 the positive end of the local is grounded If an oscilloscope is connected across the load, the ground lead of the oscilloscope will be positive and the probe top will be negative Most oscilloscopes show positive as ‘up’ and negative as ‘down’ The actual waveform seen on the screen will then appear as that shown in Fig 1-4(c) Waveform can appear up or down depending on circuit polarity, instrument polarity, and the connection between instrument and circuit Half-wave rectifies are usually limited to low power applications They take useful output from the ac source for only half the input cycle They are actually not supplying any load current half the time This limits the amount of electric energy they can deliver over a given period of time High power means delivering large amounts of energy in given time A half-wave rectifier is a poor choice in high power applications TASK Determine whether each statement is true or false Current that flows in both directions is called alternating current Diodes make good rectifiers because they will conduct in only one direction A rectifier can be used in a power supply to step up voltage Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit In a rectifier circuit, the positive end of the load will be connected to the cathode of the rectifier A half-wave rectifier supplies load current only 50 percent of the time Half-wave rectifiers are usually used in high power applications TASK Sentences in a text are held together by grammar links Now mark the grammar links in this paragraph by joining the words in italics with the words they refer to Another very important force in engineering is the one caused by elasticity A good example of this is a spring Springs exert more force the more they are stretched This property provided a way of measuring force A repeated noun becomes a pronoun Springs become they A word replaces an earlier expression Force in engineering becomes one A word replaces a whole sentences or clause Spring exert more force the more they are stretched becomes this property When the AC voltage is applied to the search coil, a magnetic field is produced around it If there is a metal object under ground, the field induces an electric current in the object The induced current in turn creates a magnetic field around the object This induces a voltage in the search coil The induced voltage is converted into an audible note by the circuitry in the box This sound guides the treasure hunter to the buried object Look back in the text and find the reference for the word in italics … , they are good rectifiers … If it were not for the diode … it can be called direct current … end which contacts the cathode of the rectifier … This may seem confusing … It represents only the positive half of … … This causes the positive half of the … … They take useful output from… … electric energy they can deliver TASK Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit Put the word in bracket in the correct word form Alternating current flows in both (direct) Electronic circuits often require much voltage (low) Transformers are used to step down the voltage to the level (need) The positive end of the load to the cathode end of the rectifier (connection) Wave-form can appear up or down on circuit polarity, instrument polarity, and the between instrument and circuit (depend/connect) A half-wave rectifier is a poor in (choose) Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự high power applications Part I – Electronics – Unit Unit 2: Electronics in the home - Find out the meaning of these abbreviations: IC, CD, Hi-fi - Read quickly through the text and write down the items mentioned Electronics began at the start of the twentieth century with the invention of the vacuum tube The first devices for everyday use were radios, followed by televisions, record players, and tape recorders These devices were large and used a lot of power The invention of the transistor in 1947 meant that much smaller, low powered devices could be developed A wide variety of electronic devices such as hi-fi (high fidelity) units and portable radios become common in the home It was not until 1958 that microelectronics began with the development of ICs (Integrated Circuits) on silicon chips This leads to a great increase in the use of electronics in everyday items The introduction of the microprocessor allowed electronics to be used for the control of many common processes Microprocessors are now used to control many household items such as automatic washing-machines, dishwashers, central heating systems, sewing machines and food processors Electronic timers are found in digital alarm clocks, water heaters, electric cookers, and microwave ovens Telephones use electronics to provide automatic dialing and answer phone facilities New entertainment devices have been developed such as video recorders and CD (Compact Disc) players In the future, electronics are likely to become even more common in the home multimedia entertainment systems and computer controlled robots are developed TASK Fill the gaps in this table with the help of the text DATE INVENTION APPLICATIONS IN THE HOME Early 20th century Transistor 1958 Automatic washing machines Future Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit TASK Use the space below to make a list of ways in which you think electronics may be used in the home in the future TASK Adjective and noun formation Use the suffixes in the boxes to write the adjective formed from the nouns and nouns formed form the verbs -ic -es -al -ive Noun -ant -ful Adjective Centre Electricity Portability Digit Constant Use -ion -ment -er/ier -or Verb -ty -ce Noun Invent Record Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit Amplify Entertain Use Vary Resist Collect Complete the sentence with verb and adjective or a noun form the box People change their mind for a of reasons Microelectronics began with the of ICs on silicon chips New entertainment devices have been developed such as video and CD (Compact Disc) player New devices have been developed such as video recorder and CD (Compact Disc) players Electronics timers are found in alarm clocks and water heater The EMF is 1.5V and the internal about 50 Ω Have characteristics that make them very in electronic circuits Batteries are often used for equipment An current, voltage, or charge is one that is produced by 10 The carbon rod is in contact with the positive electrode is called the current 11 NiCad batteries have such as a small internal resistance that the charger must produce a current output 12 John is a regular of Holland’s health-care system Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit Unit 3: Operational amplifiers Integrated circuits technology has had quite an impact on modern electronic design Integrated circuits have given designers high performance for low cost In the linear field, perhaps the best example is the modern operational amplifier There are no perfect amplifiers through modern operational amplifiers approach perfection They have characteristics are as follows: Common-mode rejection This gives them the ability to reduce hum and noise High input impedance They will not ‘load down’ a high-impedance signal source High gain They have ‘gain to burn’ which can be reduced by using feedback Low output impedance They are able to deliver a signal to a low-impedance load No signal-stage amplifier circuit can rate high in all the above characteristics An operational amplifier is actually a combination of several amplifier stages Refer to Fig 3-1 The first section of this combination circuit is a differential amplifier Differential amplifiers have common-mode rejection and high input impedance Some operational amplifiers may use field-effect transistors in this first section for even better input impedance The second section of Fig 3-1 is another differential amplifier This allows the differential output of the first section to be used Thus, common-mode rejection, maximum signal swing, and additional gain are all realized The third section of Fig 3-1 is a common collector, or emitter-follower stage This configuration is known for its low output impedance Notice that the output is a single terminal No differential output is possible This is usually referred to as a single-ended output Most electronic applications require only a single-ended output A single-ended output terminal can show only one phase with respect to ground This is why in Fig 3-1 one input is marked non-inverting and the other is marked inverting The non-inverting input will be in-phase with the output terminal The inverting input will be 180 out of phase with the output terminal Figure 3-2 shows the amplifier in a simplified way Notice the triangle Often triangles are used in schematic diagram to represent amplifiers Also notice that the inverting input is marked with a minus (-) sign and the non-inverting input is marked with a plus (+) sign This is standard practice in linear diagrams Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự Part I – Electronics – Unit Many circuits today are integrated Everything is in one little package A technician can not see inside the package or make any internal measurements Therefore, it is seldom necessary to show the schematic details of the internal circuit Fig 3-3 is an example of the standard way of showing an operational amplifier Modern operational amplifiers approach perfection They have the desirable characteristics listed earlier Such amplifiers were originally used in analog computes They performed mathematical operations This is where they got the name “operational amplifiers”, or “op-amps” Op-amplifiers are very popular, mainly because they are available in compact, integrated form at very reasonable costs TASK Answer the following questions Refer to Fig which section of the amplifier operated as an emitter follower to produce low output impedance? Refer Fig 1A signal is applied to the inverting input terminal What is the phase of the signal that appears at the output terminal as compared to the input signal? Refer to Fig is the output of the amplifier differential or single-ended? TASK Match a line in A with a line in B An operational amplifier Have Most electronic applications Will be a combination of several amplifier stage b common-mode rejection and a high input impedance c a single-ended output A technician can not see Is inside the package or make any internal measurements Op-amps are very popular Require d in-phase with the output terminal The non-inverting input Therefore e it is seldom necessary to show the schematic details of the internal circuitry Differential amplifiers Because f they are available in compact integrated form at very reasonable costs TASK Here are some circuit symbols Label them and describe their function Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 10 Part I – Electronics – Unit Even though power gain seems to be the important idea, some amplifiers are classified as voltage amplifiers In some circuits, only the voltage gain is mentioned This is especially true in amplifiers designed to handle very small electric signals You will run across many voltage amplifiers or small signal amplifiers in electronic devices, you should remember that they provide power gain, too Amplifiers designed to handle large signals are usually called power amplifiers In the electronic system of Fig 5-2 the speaker requires several watts for good volume The signal from the pickup arm is a fraction of a milliwatt (mW) A total power gain of thousands is needed However, only the final largesignal amplifier is called a power amplifier SELF TEST Determine whether each statement is true or false An amplifier needs an input signal and a power supply to develop output signal An amplifier has a voltage gain of 50 If the input signal is mV the output signal should be 50 mV The input signal to an amplifier is mA The output signal is 10 mA The amplifier has a current gain of 10 W A step transformer is a true voltage amplifier All amplifiers have power gain TASK Each of these verbs has a related noun ending in –er or –or which refers to an instrument or component Complete the column of nouns You have met these nouns in this and earlier units Ex: Record → recorder VERBS NOUNS Indicate Transmit Transform Measure Charge Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 17 Part I – Electronics – Unit Rectify Amplify Collect Detect Tune Process Oscillate Transistors Transistors make good amplifiers That can provide the power gain that is needed There are several important types of transistors This chapter will be mainly concerned with the bipolar junction transistors Bipolar junction transistors are similar to junction diodes, but one more junction is included Fig 5-3 shows one way to make a transistor A P-type semiconductors region is located between two N-type semiconductors regions The polarity of thee regions is controlled by the valence of the materials used in the doping process The transistor regions shown in Fig 5-3 are named emitter, base, and collector The emitter is very rich in current carriers Its job is to send its carrier in to base region and then on to the collector The collector collects the carriers The emitter emits the carriers The base acts as the control region As will be seen later, the base can allow few for many carriers to flow from the emitter to the collector The transistor of Fig 5-3 is bipolar because both holes and elections will take part in the current flow through the device The N-type regions contain free electrons which are negative carriers The P-type region contains free holes which are positive carriers Two (bi) polarities carriers are present Note that there are also two PN junctions in the transistor It is a bipolar junction transistor The transistor shown in Fig 5-3 would be classified as an NPN transistor Another way to make a bipolar junction is to make the emitter and collector of Ptype material and the base of N-type material This type would be classified as a PNP transistor Fig 5-4 shows both possibilities and the schematic symbols for each You should memorize the symbols Remember that the emitter lead is always the one with the arrow Also remember that if the arrow is NOT pointing in, the transistor is an NPN type Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 18 Part I – Electronics – Unit The two transistor junctions must be biased properly This is why you can not replace an NPN transistor with a PNP transistor The polarities would be wrong Transistor bias is shown in Fig 5-5 The collector-base junction must be reverse-biased for proper operation In an NPN transistor, the collector will have to be positive with respect to the base In a PNP transistor, the collector will have to be negative with respect to the base PNP and NPN transistors are not interchangeable The base-emitter junction must be forward biased, as shown in Fig 5-5 This makes the resistance of the emitter junction very low as compared with the resistance of the collector-base junction A forward-biased semiconductor junction has low resistance Fig 5-6 compared the two junction resistance The large difference in junction resistance makes the transistor capable of power gain Assume that a current if flowing through the two resistance showns in Fig 5-6 Power can be calculated by P I2 R The power gain from Rbe to Rcb could be established by calculating the power in each and dividing: Pgain I RCB I R BE If the current through RCB were equal to the current through RBE, I2 would be cancelled out and the power gain would be Pgain RCB R BE Actually, the currents are not equal in transistor, but they are very close Thus, we are making only a small error A typical resistance value for RCB might be 10,000Ω It is high since the collector base junction is reverse-biased A typical value for RBE might be 100Ω It is low because the base emitter junction is forward-biased The power gain for this typical would be: Pgain RCB 10,000 100 RBE 100 Perhaps the biggest puzzle is why the current the reverse-biased junction as high as the current through the forward-biased junction Diode theory tells us to expect almost no current through a reverse-biased junction This is true in a diode but not true in the collector-base junction of a transistor Fig 5-7 shows why the collector-base current is high The collector-base voltage VCB produces a reverse bias across the collector-base junction The baseĐiện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 19 Part I – Electronics – Unit emitter voltage VBE produces forward bias across the base-emitter junction If the transistor were simply two diode junctions, the results would be: - IB and IE would be high - IC would be zero The base region of the transistor is very narrow (about 0.0025 cm, or 0.001 in) The base region is lightly doped It has only a few holes It is not likely that an electron coming from the emitter will find a hole in the base with which to combine With so few electron-hole combinations in the base region, the base current is very low The collector is an N-type region but is charged positively by VCB Since the base is such a narrow region, the positive field of the collector is quite strong and the great majority of the electrons coming from the emitter attracted and collected by the collector Thus, - IE and IC high - IB is low The emitter current of Fig 5-7 is the highest current in the circuit The collector current is just a bit less Typically, about 99 percent of the emitter carriers go on to the collector About percent of the emitter carriers combines with carriers in the base and become base current The current equation for Fig 5-7 is IE = I C + I B By using typical percentages it can be stated as 100% = 99% + 1% The base current is quite small but very important Suppose, for example that the base lead of the transistor in Fig 5-7 is opened With the lead open, there can be no base current The two voltages VCB and VBE would add in series to make the collector positive with respect to the emitter You might guess that current would continue to flow from the emitter to the collector, but it does not With no base current, there will be no emitter current and no collector current The base-emitter junction must be forward-biased for the emitter to emit Opening the base lead removes this forward bias If the emitter in not emitting, there is nothing for the collector to collect Even though the base current is very low, it must be present for the transistor to conduct from emitter to collector Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 20 Part I – Electronics – Unit The fact that a flow base current controls much higher currents in the emitter and collector is very important This shows how the transistor is capable of good current gain TASK These verbs in the box are often used in electronics Conduct, emit, rectify, sample, dissipate, process, record, suppress Fill the gaps in these sentences with an appropriate verb from the list above Make sure the verb is in the correct form Computers data You can sound on the tape A bridge circuits is used to alternating current produce direct current All metals, and some non-metals such as carbon, electricity To prevent radio interference, you must any interference such as car ignition systems sources Power transistors ……………… heat Therefore they must be mount on a heat sink The electron gun is a CRT ………………… a stream of electrons When recording a CD, sound is ………………… 44,100 times every second Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 21 Part I – Electronics – Unit Unit 6: Conductors, insulators and semiconductors If we connect a battery across a body there is a movement of free electrons towards the positive end This movement of electrons is an electric current All materials can be classified into three groups according to how readily they permit an electric current to flow These are: conductor, insulator and semiconductor In the first category, metals are substances which provide an easy path for an electric current All metals are conductor However, some metals not conduct well Manganese, for example, is a poor conductor Copper is a good conductor, therefore it is widely used for cables A non-metal which conducts well is carbon Salt water is an example for a liquid conductor A material which does not easily release electrons is called an insulator Rubber, nylon, porcelain and air are all insulators There are no perfect insulators All insulators will allow some flow of electrons, however this can usually be ignored because the flow they permit is so small Semiconductors are midway between conductor and insulator Under certain conditions they allow a current to flow easily but under others they behave as insulators Germanium and silicon are semiconductors Mixtures of certain metallic oxides also act as semiconductors These are known as thermistors The resistance of thermistor falls rapidly as their temperature rises They are, therefore used in temperature – sensing devices TASK Read the text and decide if these statements are true or false in relation to the information in the text Electrons flow from positive to negative Copper provides an easy path for an electric current All metals are good conductors All good conductors are metals Air is not a perfect insulator Rubber readily releases electrons The resistance of a thermistor is higher at low temperatures than at high temperatures TASK Contextual reference Rewrite the following sentences, replacing the words in italics with expressions from the passage that have similar meanings to: The flow of free electrons is an electric current Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 22 Part I – Electronics – Unit Materials in the first group are called conductors Materials providing a path for an electric current are conductors All insulators permit some flow of electrons Germanium sometimes acts as an insulator and sometimes as a conductor TASK Look back in the text and find the reference for the words in italics What the pronouns in these sentences refer to? All materials can be classified into three groups according to how readily they permit an electric current to flow a Three groups b All materials c Free electrons Under certain conditions they allow a current to flow easily but under others they behave as insulators a Conductors b Semiconductors c Insulators These are known as thermistors a Metallic oxides metallic oxides b Semiconductors c mixtures of certain They are therefore used in temperature-sensing devices a Thermistors b Semiconductors Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự c Metallic oxides 23 Part I – Electronics – Unit Language focus Adjective clauses An adjective clause is a dependent clause that modifies a noun It describes, identifies, or gives further information about a noun (An adjective clause is also called a relative clause) Using subject pronouns: who, which, that Who is used for people Which is used for things That is used for both people and things Note: An object pronoun is often omitted from an adjective clause (A subject pronoun, however, may not be omitted) Punctuation of adjective clause: a Don’t use commas if the adjective clause is necessary to identify the noun it modifies b Use commas if the adjective clause simply gives additional information and it is not necessary to identify the noun it modifies Exercise 1: Combine the sentences, using the second structure as an adjective clause Example: - The error sensor output is fed to the controller - The controller sends a signal to the power supply of the motor → The error sensor output if fed to the controller which sends a signal to the power supply of the motor - The rotor contains an armature - Armature is a set of wire loops wound on a steel core (which) - This device provides a 50Ω resistance discharge path for the defibrillator paddles - Discharge path stimulates the torso resistance (That) - The instrument will then perform a calibration and self-test procedure - Self-test procedure consists of checking the position of the feed table (which) - The sequence number is displayed in the centre of the top line of the display - The sequence number will be assigned to the next test (that) - Test results are listed in the package insert - Test results should be obtained (that) Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 24 Part I – Electronics – Unit Exercise 2: Add commas where necessary The display changes to the Test Screen which shows the sequence number of the strip being tested Do not use any material that will scratch the feed table insert The moving coil which gives the instrument its name is composed of fine copper wire wound on a thin rectangular aluminum former The oxygen content of the air flowing into the bellows is controlled by a percentage control valve which regulates the resistance to room air and oxygen appropriately The direction of the air in the pneumatic system is determined by the main solenoid which is switched appropriately by the system electronics The third terminal of the pot is connected to the zero voltage supply rail which is earthed The envelope contains nitrogen which helps to prevent corrosion of the contact Exercise 3: Short relative clauses We can join these sentences by using a relative clause - The lines are arranged in two groups - The lines carry the supply → The lines which carry the supply are arranged in two groups Relative clauses with certain active verbs can be shorten by omitting the relative words and changing the verb to its – ing form These verbs include: Carry Contain Consist of form hold measure We can shorten the relative clause like this: The lines carrying the supply are arranged in two groups The lines are suspended from insulators The insulators are made of porcelain The lines are suspended from insulators which are made of porcelain Relative clause like this with passive verbs can be shortened by omitting the relative word and the verb to be: The lines are suspended from insulators made of porcelain Now link each group of sentences into one sentence Use short relative clause where possible (Number can not be shortened) Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 25 Part I – Electronics – Unit - In Britain electrical energy is fed to the National Grid - The energy is generated in power stations - The energy passes through a transformer - The transformer steps up the voltage to 132, 275 or 400 kV - The transmission lines are usually arranged in groups of three … overhead conductors - The lines carry the supply - The overhead conductors are suspended from porcelain insulators - Energy from power stations is located in built-up areas - The power stations are located in built-up areas - For voltages up to 400 kV cables are used - These cables contain oil under low pressure Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 26 Part I – Electronics – Unit Unit 7: Circuit element Current moves from a point of high potential energy to one of low potential It can only so if there is a path for it to follow This path is called an electric circuit All circuits contain four elements: a source, a load, a transmission system and a control The source provides the electromotive force This establishes the difference in potential which makes currents flow possible The source can be any device which supplies electrical energy For example, it may be a generator or a battery The load converts the electrical energy from the source into some other form of energy For instance, a lamp changes electrical energy into light and heat The load can be any electrical device The transmission system conducts the current round the circuit Any conductor can be part of a transmission system Most systems consist of wires It is often possible, however, for the metal frame of a unit to be one section of its transmission system For example, the metal chassis of many electrical devices are used to conduct current Similarly the body of a car is part of its electrical transmission system The control regulates the current flow in the circuit It may control the current by limiting it, as does a rheostat, or by interrupting it, as does a switch Study figure In this simple flashlight circuit, the source comprises three 1.5V cells in series The load is a 0.3W bulb Part of the transmission system is the metal body of the flashlight, and the control is a sliding switch Compare figure The function of this circuit is to operate a television camera Here the source is a battery of solar cells A solar cell is an electric cell which converts sunlight into the electrical energy The load is the television camera The transmission system is the connecting wires The control is a relay actuated by transmissions from ground control Although the function of this circuit is much more complex than that of the flashlight, it too consists of the four basic elements TASK Decide whether these statements are true or false in relation to the information in the text If you think a statement is false, change it to make it true A difference in potential is required so that current can flow in a circuit A generator is a source of electromotive force Loads convert electrical energy into light and heat Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 27 Part I – Electronics – Unit Transmission systems must consist of wires A rheostat may be used as a control The load in the flashlight circuit is a bulb The source in the satellite circuit is a solar cell The current flow in the satellite circuit is regulated by a relay The flashlight circuit differs basically from the satellite circuit TASK Rewrite the following sentences, replacing the words in italics with expressions from the passage that have a similar meaning too A lamp converts electrical energy into light The generator provides the circuit with electromotive force The metal frame of the oscilloscope is part of its transmission system The rheostat controls the current flow in the circuit A battery of solar cells supplies power to the circuit TASK What the pronouns in italics in these sentences refer to? Current moves from a point of high potential energy to one of low potential a Current b Energy c A point For example, it may be a generator or a battery a The source b A device c Electromotive force It is often possible, however, for the metal frame of a unit to be one section of its transmission system a The metal frame’s b The unit’s c The circuit’s Although the function of this circuit is much more complex than that of the flashlight, it too consists of the four basic elements a The circuit b The function Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự c The flashlight 28 Part I – Electronics – Unit Language focus Passive voice We normally make passive form of a verb by using tenses of the auxiliary “be” followed by the past participle (PP) of the verb (For “Get” as a passive auxiliary) We often choose to use passive structures when we want to talk about an action, but are not interested in saying who or what does/did it Passive without “agents” are common in academic and scientific writing for the reason Example: We use microprocessors to signal processing on an ECG waveform Microprocessors are used to signal processing on an ECG waveform Exercise 1: Read the following sentences and fill in the gaps using the appropriate form of the verb in brackets Information on these four conditions will …………… (feed) in to an AND gate as all four must …………… (satisfy) for the motor to run Various colors of light …………… (produce) depending on the phosphor …………… (use) In 1952 the Pacemaker …………… (use) clinically by Paul M 2011 as a external device If an error …………… (detect) by the instrument, an appropriate error massage …………… (display) Do not attempt to test a new specimen until “START” …………… (display) After the results …………… (print), the prefix will return to the assigned number Test results that should …………… (obtain) are …………… (list) in the package insert Exercise 2: Short relative clause Study these sentences: - A telephone dial consists of a Rota table plate The plate has ten finger holes in it We can link them using a relative clause: A telephone dial consists of a Rota table plate which has ten finger holes in it We can shorten the relative clause in two ways: A telephone dial consists of a Rota table plate having ten finger holes in it A telephone dial consists of a Rota table plate with ten finger holes in it Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 29 Part I – Electronics – Unit Sometimes we can reduce a relative clause to an adjective: Example: High quality instruments use resistors The resistors are wire-wound High quality instruments use resistors which are wire-wound High quality instruments use wire-wound resistors Make this paragraph shorter by reducing the relative clauses Using all the methods of reduction you have learned The telephone is an instrument which enables us to transmit speech via wires The body of the telephone contains an induction coil, capacitors, resistors, a regulator, which controls the sensitivity of the instrument, and a bell The handset contains a microphone and a receiver which are enclosed by screw caps at the ends of the handset The bell contains a hammer which is operated by a solenoid The hammer is set between two domes which are eccentrically mounted The dial is mounted on the face of the telephone It consists of a Rota table plate which has ten finger holes in it A wheel, which has ten slots cut in its edge which match the finger hole, is fitted below the dial When the plate is turned, the wheel causes spring contacts to open and close a number of times which correspond to the number dialed This transmits pulses down the line causing selectors, which connect the calling line to the line which is called, to operate Điện Tử Y Sinh – Học Viện Kỹ Thuật Quân Sự 30 WHAT DO THESE ABBREVIATIONS STAND FOR? ADC Analogue-to-digital converter AC Alternating current AF Audio frequency CT Computer tomography CRT Cathode ray tube CRO Cathode ray oscilloscope CPU Central processing unit CDs Compact discs CAD Computer aided design 10 CMOS Complementary metal oxide semiconductor 11 DC Direct current 12 EST Extended-self-test 13 FAX Facsimile 14 HDTV High definition television 15 I/O Input/output 16 ICs Integrated circuits 17 ISDN Integrated services digital network 18 LANs Local area networks 19 LCD Liquid crystal display 20 LED Light-emitting diode 21 LPs Long-play albums 22 LP Long-play record 23 LDR Light-dependent resistor 24 MS I Medium scale integration 25 POST Power-on self-test 26 PSTN Public switching telephone network 27 ROM Read-only memory 28 RAM Random-access memory 29 RF Radio frequency 30 TTL Transistor-transistor logic 31 UHF Ultra-high frequency 31 ... formed form the verbs -ic -es -al -ive Noun -ant -ful Adjective Centre Electricity Portability Digit Constant Use -ion -ment -er/ier -or Verb -ty -ce Noun Invent Record Điện Tử Y Sinh – Học Viện... approach, - A increased interaction between psychology and other sciences which study people Common cold has several symptoms: - Feel very unpleasant - Your head aches - You sneeze and cough - Your... be positive Look at Fig 1- 2 to see if this so Fig 1- 4 (a) shows the input waveform to the rectifier circuits of Figs 1- 2 and 1- 3 Two complete cycles are shown In Fig 1- 4 (b) the waveform that appears