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BASIC ELECTRONIC COMPONENTS MODEL ECK-10 Coils Capacitors Resistors Others Transformers (not included) Semiconductors Instruction Manual by Arthur F. Seymour MSEE It is the intention of this course to teach the fundamental operation of basic electronic components by comparison to drawings of equivalent mechanical parts. It must be understood that the mechanical circuits would operate much slower than their electronic counterparts and one-to-one correlation can never be achieved. The comparisons will, however, give an insight to each of the fundamental electronic components used in every electronic product. ELENCO® Copyright © 2016, 1994 by ELENCO® Electronics, Inc. All rights reserved. Revised 2016 REV-O 753254 No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
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RESISTORS RESISTORS, What do they do? The electronic component known as the resistor is Electrons flow through materials when a pressure best described as electrical friction. Pretend, for a (called voltage in electronics) is placed on one end moment, that electricity travels through hollow pipes of the material forcing the electrons to “react” with like water. Assume two pipes are filled with water each other until the ones on the other end of the and one pipe has very rough walls. It would be easy material move out. Some materials hold on to their to say that it is more difficult to push the water electrons more than others making it more difficult through the rough-walled pipe than through a pipe for the electrons to move. These materials have a with smooth walls. The pipe with rough walls could higher resistance to the flow of electricity (called be described as having more resistance to current in electronics) than the ones that allow movement than the smooth one. electrons to move easily. Therefore, early experimenters called the materials insulators if they Pioneers in the field of electronics thought electricity had very high resistance to electon flow and was some type of invisible fluid that could flow conductors if they had very little resistance to through certain materials easily, but had difficulty electron flow. Later materials that offered a medium flowing through other materials. In a way they were amount of resistance were classified as correct since the movement of electrons through a semiconductors. material cannot be seen by the human eye, even with the best microscopes made. There is a When a person designs a circuit in electronics, it is similarity between the movement of electrons in often necessary to limit the amount of electrons or wires and the movement of water in the pipes. For current that will move through that circuit each example, if the pressure on one end of a water pipe second. This is similar to the way a faucet limits the is increased, the amount of water that will pass amount of water that will enter a glass each second. through the pipe will also increase. The pressure on It would be very difficult to fill a glass without the other end of the pipe will be indirectly related to breaking it if the faucet had only two states, wide the resistance the pipe has to the flow of water. In open or off. By using the proper value of resistance other words, the pressure at the other end of the in an electronic circuit designers can limit the pipe will decrease if the resistance of the pipe pressure placed on a device and thus prevent it increases. Figure 1 shows this relationship from being damaged or destroyed. graphically. SUMMARY: The resistor is an electronic component that has electrical friction. This friction opposes the flow of electrons and thus reduces the Water Tank voltage (pressure) placed on other electronic components by restricting the amount of current that Low Resistance High Pressure can pass through it. Pipe Through Same Size Opening High Resistance Pipe (rough walls) Low Pressure Figure 1 -1-
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RESISTORS RESISTORS, How are they made? There are many different types of resistors used in The value of wirewound resistors remain fairly flat electronics. Each type is made from different with increasing temperature, but change greatly with materials. Resistors are also made to handle frequency. It is also difficult to precisely control the different amounts of electrical power. Some value of the resistor during construction so they resistors may change their value when voltages are must be measured and sorted after they are built. placed across them. These are called voltage dependent resistors or nonlinear resistors. Most Ceramic Rod resistors are designed to change their value when the temperature of the resistor changes. Some resistors are also made with a control attached that allows the user to mechanically change the Wire resistance. These are called variable resistors or Protective Coating End Cap potentiometers. Figure 2 shows physical shapes of some different types of resistors. Carbon Composition Figure 3 THE CARBON COMPOSITION RESISTOR By grinding carbon into a fine powder and mixing it with resin, a material can be made with different resistive values. Conductive leads are placed on Carbon Film each end of a cylinder of this material and the unit is then heated or cured in an oven. The body of the Variable resistor is then painted with an insulating paint to Figure 2 prevent it from shorting if touched by another component. The finished resistors are then measured and sorted by value (Figure 4). If these THE WIREWOUND RESISTOR resistors are overloaded by a circuit, their resistance will permanently decrease. It is important that the The first commercial resistors made were formed by power rating of the carbon composition resistor is wrapping a resistive wire around a non-conducting not exceeded. rod (see Figure 3). The rod was usually made of some form of ceramic that had the desired heat properties since the wires could become quite hot Insulating Paint Carbon & Resin during use. End caps with leads attached were then Mixture placed over the ends of the rod making contact to the resistive wire, usually a nickel chromium alloy. Conductive Wire Figure 4 -2-
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RESISTORS CARBON FILM RESISTORS THE VARIABLE RESISTOR Carbon film resistors are made by depositing a very When a resistor is constructed so its value can be thin layer of carbon on a ceramic rod. The resistor is adjusted, it is called a variable resistor. Figure 6 then protected by a flameproof jacket since this type shows the basic elements present in all variable of resistor will burn if overloaded sufficiently. Carbon resistors. First a resistive material is deposited on a film resistors produce less electrical noise than non-conducting base. Next, stationary contacts are carbon composition and their values are constant at connected to each end of the resistive material. high frequencies. You can substitute a carbon film Finally, a moving contact or wiper is constructed to resistor for most carbon composition resistors if the move along the resistive material and tap off the power ratings are carefully observed. The desired resistance. There are many methods for construction of carbon film resistors require constructing variable resistors, but they all contain temperatures in excess of 1,000OC. these three basic principles. Thin Layer Non-conductive Carbon Film of Resistive Base Material Material Wiper Movable Contact Ceramic Rod Flameproof Jacket Arm Figure 5 Stationary Contact METAL OXIDE RESISTORS Metal oxide resistors are also constructed in a Leads similar manner as the carbon film resistor with the exception that the film is made of tin chloride at Figure 6 temperatures as high as 5,000OC. Metal oxide resistors are covered with epoxy or some similar plastic coating. These resistors are more costly than other types and therefore are only used when circuit constraints make them necessary. METAL FILM RESISTORS Metal film resistors are also made by depositing a film of metal (usually nickel alloy) onto a ceramic rod. These resistors are very stable with temperature and frequency, but cost more than the carbon film or carbon composition types. In some instances, these resistors are cased in a ceramic tube instead of the usual plastic or epoxy coating. -3-
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RESISTORS RESISTOR VALUES AND MARKINGS The unit of measure for resistance is the ohm, which Note: If the third ring is gold, you multiply the first is represented by the Greek letter W. Before two digits by 0.1 and if it is silver, by 0.01. This technology improved the process of manufacturing system can identify values from 0.1W to as high as resistors, they were first made and then sorted. By 91 x 109, or 91,000,000,000W. The amount of power sorting the values into groups that represented a 5% each resistor can handle is usually proportional to change in value, (resistor values are 10% apart), the size of the resistor. Figure 8 shows the actual certain preferred values became the standard for size and power capacity of normal carbon film the electronics industry. Table 1 shows the standard resistors, and the symbols used to represent values for 5% resistors. resistors on schematics. 10 11 12 13 15 16 18 20 Resistor Symbols 22 24 27 30 33 36 39 43 1/8 Watt 47 51 56 62 68 75 82 91 1/4 Watt Table 1 1/2 Watt Regular Variable Resistors are marked by using different colored rings around their body (see Figure 7). The first ring Figure 8 represents the first digit of the resistor’s value. The second ring represents the second digit of the resistor’s value. The third ring tells you the power of ten to multiply by. The final and fourth ring represents the tolerance. For example, gold is for 5% resistors and silver for 10% resistors. This means the value of the resistor is guaranteed to be within 5% or 10% of the value marked. The colors in Table 2 are used to represent the numbers from 0 to 9. COLOR VALUE Red Orange Black 0 Brown 1 Red 2 Orange 3 Violet Gold Yellow 4 Green 5 27 X 103 = 27,000 W, Blue 6 with 5% Tolerance Violet 7 Gray 8 Figure 7 White 9 Table 2 -4-
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RESISTORS SELF TEST THEORY Circle the letter that best fits the description. 1. A flow of electrons through a material: 6. A resistor that is made by wrapping a wire around a a) Voltage c) Current ceramic rod: b) Resistance d) Conductance a) Carbon Film c) Thermistor b) Carbon Composition d) Wirewound 2. The pressure that pushes electrons through a material: 7. A resistor made by heating powder and resin in an a) Voltage c) Conduction oven: b) Current d) Resistance a) Carbon Film c) Thermistor b) Carbon Composition d) Wirewound 3. A material that has very high resistance to electron flow: 8. A resistor made by depositing a very thin layer of a) Conductor c) Resistor resistive material on a ceramic rod: b) Semiconductor d) Insulator a) Carbon Film c) Thermistor b) Carbon Composition d) Wirewound 4. A material that allows electrons to flow easily: a) Conductor c) Resistor 9. One of the preferred values for a 5% resistor: b) Semiconductor d) Insulator a) 4000W c) 77W b) 560W d) 395W 5. A material that produces electrical friction and restricts the flow of electrons: 10. The amount of wattage a resistor can handle is a) Conductor c) Resistor determined by: b) Semiconductor d) Insulator a) Value c) Current b) Voltage d) Size PRACTICE Open the bag marked “resistors” and fill in the table below. Color 1 Color 2 Color 3 Color 4 Value Percent Wattage EXTRA CREDIT Using a razor blade or sharp knife, scrape away the paint on the body of one resistor and determine the type of construction used to make it. Try and determine all of the materials used including the metals used to make the leads. -5-
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CAPACITORS CAPACITORS, What do they do? Capacitors are components that can store electrical Capacitors act the same as the pipe in Figure 9. pressure (Voltage) for long periods of time. When a When a voltage (Electrical Pressure) is placed on capacitor has a difference in voltage (Electrical one lead with respect to the other lead, electrons Pressure) between its two leads it is said to be are forced to “pile up” on one of the capacitor’s charged. A capacitor is charged by forcing a one plates until the voltage pushing back is equal to the way (DC) current to flow through it for a short period voltage applied. The capacitor is then charged to the of time. It can be discharged by letting an opposite voltage. If the two leads of that capacitor are direction current flow out of the capacitor. Consider shorted, it would have the same effect as letting the for a moment the analogy of a water pipe that has a plunger in Figure 9 move freely. The capacitor would rubber diaphragm sealing off each side of the pipe rapidly discharge and the voltage across the two as shown in Figure 9. leads would become zero (No Charge). What would happen if the plunger in Figure 9 was Pipe Filled with Water wiggled in and out many times each second? The water in the pipe would be pushed by the diaphragm then sucked back by the diaphragm. Since the movement of the water (Current) is back and forth (Alternating) it is called an Alternating Current or AC. The capacitor will therefore pass an alternating Plunger Rubber Diaphragm current with little resistance. When the push on the Sealing Center of Pipe plunger was only toward the diaphragm, the water on the other end of the diaphragm moved just Figure 9 enough to charge the pipe (transient current). Just as the pipe blocked a direct push, a capacitor clocks If the pipe had a plunger on one end, as shown in direct current (DC). An example of alternating Figure 9, and the plunger was pushed toward the current is the 60 cycle (60 wiggles each second) diaphragm, the water in the pipe would force the current produced when you plug something into a rubber to stretch out until the force of the rubber wall outlet. pushing back on the water was equal to the force of the plunger. You could say the pipe is charged and SUMMARY: A capacitor stores electrical energy ready to push the plunger back. In fact, if the when charged by a DC source. It can pass plunger is released it will move back to its original alternating current (AC), but blocks direct current position. The pipe will then be discharged or with no (DC) except for a very short charging current, called charge on the diaphragm. transient current. -6-
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CAPACITORS CAPACITORS, How are they made? There are many different types of capacitors used in pressure (low capacitance, but high working electronics. Each type is made from different voltage). By making the pipe larger and keeping the materials and with different methods. Capacitors are stiff rubber we can achieve a device that holds a also made to handle different amounts of electrical large amount of water and withstands a high amount pressure or voltage. Each capacitor is marked to of pressure (high capacitance, high working voltage, show the maximum voltage that it can withstand large size). These three types of water pipes are without breaking down. All capacitors contain the illustrated in Figure 12. The pipes follow the rule that same fundamental parts, which consist of two or the capacity to hold water, (Capacitance) multiplied more conductive plates separated by a by the amount of pressure they can take (Voltage) nonconductive material. The insulating material determines the size of the pipe. In electronics the between the plates is called the dielectric. The basic CV product determines the capacitor size. elements necessary to build a capacitor are shown in Figure 10. Paper or Plastic Insulator Lead 1 Conductive Plate Lead 2 Lead 1 Conductive Foil Lead 2 Nonconductive Material Figure 10 Figure 11 Soft Rubber Stiff Rubber THE METAL FOIL CAPACITOR Perhaps the most common form of capacitor is constructed by tightly winding two foil metal plates that are separated by sheets of paper or plastic as Large Capacity Low Capacity shown in Figure 11. By picking the correct insulating Low Pressure but can withstand material the value of capacitance can be increased High Pressure greatly, but the maximum working voltage is usually Stiff Rubber lowered. For this reason, capacitors are normally identified by the type of material used as the insulator or dielectric. Consider the water pipe with the rubber diaphragm in the center of the pipe. The Larger Size diaphragm is equivalent to the dielectric in a capacitor. If the rubber is made very soft, it will stretch out and hold a large amount of water, but it will break easily (large capacitance, but low working High Capacity and can withstand High Pressure voltage). If the rubber is made very stiff, it will not stretch far, but will be able to withstand higher Figure 12 -7-
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CAPACITORS DIELECTRIC CONSTANT, What is it? THE VARIABLE CAPACITOR The dielectric (rubber diaphragm in the water pipe To make a variable capacitor, one set of stationary analogy) in a capacitor is the material that can aluminum plates are mounted to a frame with a withstand electrical pressure (Voltage) without small space between each plate. Another set of appreciable conduction (Current). When a voltage is plates are mounted to a movable shaft and applied to a capacitor, energy in the form of an designed to fit into the space of the fixed plates electric charge is held by the dielectric. In the rubber without touching them. The insulator or dielectric in diaphragm analogy the rubber would stretch out and this type of variable capacitor is air. When the hold the water back. The energy was stored in the movable plates are completely inside the fixed rubber. When the plunger is released the rubber plates, the device is at minimum capacitance. The would release this energy and push the plunger shape of the plates can be designed to achieve the back toward its original position. If there was no proper amount of capacitance versus rotation for energy lost in the rubber diaphragm, all the energy different applications. An additional screw is added would be recovered and the plunger would return to to squeeze two insulated metal plates together its original position. The only perfect dielectric for a (Trimmer) and thus set the minimum amount of capacitor in which no conduction occurs and from capacitance. which all the stored energy may be recovered is a perfect vacuum. The DIELECTRIC CONSTANT (K) Trimmer is the ratio by which the capacitance is increased when another dielectric replaces a vacuum between Fixed Plates two plates. Table 3 shows the Dielectric Constant of various materials. Shaft Air, at normal pressure 1 Mica 7.5 Alcohol, ethyl (grain) 25 Paper, manila 1.5 Beeswax 1.86 Paraffin wax 2.25 Movable Plates Castor Oil 4.67 Porcelain 4.4 Frame Glass flint density 4.5 10 Quartz 2 Glycerine 56 Water, distilled 81 Table 3 Figure 13 -8-
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CAPACITORS CAPACITANCE, How is it calculated? The amount of charge a capacitor can hold (capacitance) is measured in Farads. In practice, one farad is a very large amount of capacitance, 0.01 inch making the most common term used micro-farad or one millionth of a farad. There are three factors that Glass K=10 determine the capacitance that exist between two conductive plates: 1. The bigger the plates are (Surface Area), the higher the capacitance. Capacitance (C) is directly proportional to Area (A). 2. The larger the distance is between the two plates, the smaller the amount of 1 inch capacitance. Capacitance (C) is indirectly proportional to distance (d). 1 inch 3. The larger the value of the dielectric constant, the more capacitance (Dielectric constant is equivalent to softness of the Figure 14 rubber in our pipe analogy). The capacitance (C) is directly proportional to the Dielectric Constant (K) of the insulating material. From the above factors, the formula for capacitance in Farads becomes: CAPACITOR VALUES AND MARKINGS C = 0.244K A(N-1) Picofarads * The older styles of capacitors were marked with d colored dots or rings similar to resistors. In recent years, the advances in technology has made it C = Capacitance in Picofarads (Farad x 10-12) easier to print the value, working voltage, tolerance, and temperature characteristics on the body of the K = Dielectric Constant capacitors. Certain capacitors use a dielectric that A = Area of one Plate in square inches requires markings to insure one lead is always kept N = Number of Plates at a higher voltage than the other lead. Figure 15 shows typical markings found on different types of d = Distance between plates in inches capacitors. Table 4 gives the standard values used and the different methods for marking these values. Example Calculation for Capacitor shown in Figure 14. C = 2.24 x (1 x 1)(2 - 1) / (.01) = 224 Picofarads or 0.000224 Microfarads. +16V B * If A and d are in centimeters change 0.224 to +10 682K F 25V K m 0.0885. 2200 F 25Vm 10 Tantalum Disc Radial Axial Chip Electrolytic Electrolytic Electrolytic (no markings) Figure 15 -9-
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CAPACITORS Voltage Code Cap. Value Typical Markings Tolerance (%) Markings 1 2 3 4 5 6 7 4 0G 100pF 100pF 101 +5% J 5.5 0L .001mF .001 102 +10% K 6.3 0J .015mF .015 152 +20% M 10 1A .002mF .002 202 –10% +30% Q 16 1C .0022mF .0022 222 –10% +50% T 25 1E .003mF .003 302 –20% +80% Z 35 1V .033mF .033 333 SPECIAL A 50 1H .047mF .047 473 63 1J .05mF .05 R05 Temperature 80 1K .068mF .068 R068 Markings 100 2A .1mF .1 104 NP0 {<10ppm / OC} 110 2Q .15mF .15 154 N100 {<100ppm / OC} 125 2B .2mF .2 204 N220 {<220ppm / OC} 160 2C 2.2mF 2.2 2R2 N820 {<820ppm / OC} 180 2Z 22mF 22 22 Y5F 200 2D 100mF 100 100 Y5T 220 2P 220mF 220 220 Y5V 250 2E 470mF 470 470 X5F 315 2F 1000mF 1000 1000 Z5U Capacitor markings vary greatly from one manufacturer may use an R to represent the manufacturer to another as the above table shows. decimal point. The tolerance is usually printed Voltages may be marked directly (200V) or coded directly on the capacitors. When it is omitted, the (2D). The value of capacitance may be marked standard tolerance is assumed to be +80% to –20% directly on the part as shown in columns 4 and 5 for electrolytics. Capacitance change with (note that .001mF and 1000mF have the same temperature is coded in parts per million per degree marking, but the difference in size makes the value C, {N220 = 220/1,000,000 or .022%}, or by a obvious). The number 102 may also be used to temperature graph. See manufacturers represent 1000 (10+2 zeros). In some instances the specifications for complete details. CAPACITOR SYMBOLS Figure 16 shows the schematic symbols used to represent capacitors. The + symbol indicates that the capacitor is Figure 16 + polarized and the lead marked with the + sign must always – have a higher voltage than the other lead. The curved plate, plate with sides, and minus sign also indicate the capacitor is polarized and these leads must always be at a lower voltage than the other lead. The arrow crossing through the capacitor indicates of capacitance is variable. Standard Polarized Variable -10-
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CAPACITORS SELF TEST THEORY Circle the letter that best fits the description. 1. A flow of electrons in one direction: 7. When electrons are forced onto one plate of a a) AC Voltage c) Alternating Current capacitor: b) Direct Voltage d) Direct Current a) Polarization c) Storage b) Discharging a) Charging 2. When two conductive plates are moved closer together Capacitance will: 8. A capacitor lead that is marked with a + must always be: a) Increase c) Stay the Same a) Grounded c) At higher voltage than b) Decrease d) Vary Downwards the other lead b) At highest voltage d) b & c 3. The name given to the material between a capacitor’s plates: 9. A small disc capacitor marked 100 has a value of: a) Air c) Conductor a) 100mF c) 100pF b) Dielectric d) Insulator b) .00001F d) 100F 4. Electrons flowing in and out of a wire: 10. A large electrolytic capacitor marked 100 has a value a) AC Voltage c) Alternating Current of: b) Direct Voltage d) Direct Current a) 100mF c) 100pF b) .00001F d) 100F 5. If the size of the conductive plates is increased, capacitance will: 11. If a dielectric is changed from air to distilled water the a) Increase c) Stay the Same capacitance will: b) Decrease d) Vary Downwards a) remain the same c) decrease b) increase 81 times d) drop in half 6. A capacitor will block: a) AC Voltage c) Alternating Current 12. A dielectric that stores energy with no loss: b) Direct Voltage d) Direct Current a) Does not exist c) Pure Glass b) Air d) A perfect vacuum PRACTICE Open the bag marked “capacitors” and fill in the table below. Type Capacitance Working Polarized Other Value Voltage (Y/N) Markings Table 4 EXTRA CREDIT 10mF What happens to the total capacitance if you connect two ? mF capacitors as shown in Figure 17. Hint, use water pipe analogy and try to calculate equivalent if one water pipe. 20mF Figure 17 -11-
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INDUCTORS INDUCTORS, What do they do? The electronic component known as the inductor is Since Inductors are made by coiling a wire, they are best described as electrical momentum. In our water often called Coils. In practice the names Inductor pipe analogy the inductor would be equivalent to a and Coil are used interchangeably. From the above very long hose that is wrapped around itself many analogy, it is obvious that a coiled hose will pass times (see Figure 18). If the hose is very long it will Direct Current (DC), since the water flow increases contain many gallons of water. When pressure is to equal the resistance in the coiled hose after an applied to one end of the hose, the thousands of elapsed period of time. If the pressure on the gallons of water would not start to move instantly. It plunger is alternated (pushed, then pulled) fast would take time to get the water moving due to enough, the water in the coil will never start moving inertia (a body at rest wants to stay at rest). After a and the Alternating Current (AC) will be blocked. while the water would start to move and pick up The nature of a Coil in electronics follows the same speed. The speed would increase until the friction of principles as the coiled hose analogy. A coil of wire the hose applied to the amount of pressure being will pass DC and block AC. Recall that the nature of applied to the water. If you try to instantly stop the a Capacitor blocked DC and passed AC, the exact water from moving by holding the plunger, the opposite of a coil. Because of this, the Capacitor momentum (a body in motion wants to stay in and Inductor are often called Dual Components. motion) of the water would cause a large negative Table 5 compares the properties of capacitors and pressure (Suction) that would pull the plunger from inductors. your hands. Large Hose Filled with Water Plunger Water Pipe Figure 18 Capacitor Inductor Blocks Direct Current Blocks Alternating Current Passes Alternating Current Passes Direct Current Voltage in Capacitor cannot change instantly Current in an Inductor cannot change instantly Quick Voltage change produces large Current Quick Current change produces large Voltage Stores Energy in Electric Field Stores Energy in Magnetic Field Current leads Voltage Voltage leads Current Table 5 -12-
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INDUCTORS INDUCTORS, How are they made? In order to understand how inductors are made, we the coil is increased, it will take more hose to form a have to change our water pipe analogy slightly to loop, and the amount of water will therefore include the effect of magnetic fields. Consider two increase. More water means a larger “apparent pipes filled with water and small magnets attached mass”. Inductance will also increase in a coil if the to the walls of the pipes with rubber bands as shown cross sectional area increases. Inductance is in Figure 19. The moving magnets, due to the directly proportional to area. original current, pull the magnets in the second pipe and force a small current to flow in the same direction as the original current. When the rubber bands are fully stretched, the induced current will stop, even though the initial DC current is still flowing. If the original current is an AC current however, it will induce a continuous AC current in Coil 1 the second pipe because the magnets will move back and forth, pulling the magnets in the second pipe back and forth. Coil 2 Figure 20 Induced Consider the affect of adding more turns to coiled Current pipe. The amount of material to push (mass) is increased and the amount of linkage is increased due to more magnets available. This causes the “apparent mass” to increase at a greater rate than would be expected. When making an inductor, the actual inductance is directly proportional to the square of the number of turns. The final factor to consider when making a coil is the core material at the center of the coil. If our pipe wrapped around a material that contained many Initial magnets, they would also link to the magnets in the Current pipe. This would increase the “apparent mass” of the water in Figure 19 the pipe. The tiny magnets in the core Consider the two coiled pipes shown in Figure 20. would rotate as shown When the pipe is stretched out (increased length) as in Figure 21 and force in coil 1, the adjacent turns have little affect on each the water to keep other. In coil 2 (decreased length) the magnets in moving in the same each turn of the pipe are linking and the amount of direction. Placing an “apparent mass” in the pipe seems to increase. In iron core at the center Many tiny an inductor, pushing the coiled wire closer together of an inductor will magnets causes the inductance of the coil to also increase, directly increase the OUT and stretching the coil out will lower the inductance inductance by an of the coil. In other words, the inductance of a coil is amount equal to the IN indirectly proportional to its length. If the diameter of permeability of the core material. Figure 21 -13-
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INDUCTORS INDUCTANCE, How is it calculated? Reviewing how coils are made will show the Where: following: L = Inductance in microhenrys 1. Inductance of a coil is indirectly proportional to N = Number of turns the length of the coil. m = Permeability of core material 2. Inductance is directly proportional to the cross sectional area. A = Cross-sectional area of coil, in square inches l = Length of coil in inches 3. Inductance is proportional to the square of the number of turns. This formula is good only for solid core coils with 4. Inductance is directly proportional to the length greater than diameter. permeability of the core material. From the above information the formula for inductance of a simple iron core would be: L = N2mA 10l TRANSFORMERS, How are they made? Placing different coils on the same iron core as forcing the core magnet rotation (Called flux by the shown in Figure 22 produces the electronic Pros) to push the current in the opposite direction component known as the Transformer. If a DC and produce a voltage of the opposite polarity. Since current is forced through the center coil, the other the number of turns in the top coil are the same as two coils will only produce a current when the the generator coil, the voltage and current (Power original current is changing. Once the DC current that can be taken from the coil) will also be equal. reaches a constant value, the other two coils will This ability to transform AC voltages and AC “unlink” and produce no flowing current if loaded. If currents influenced early experimenters to call this the generator voltage is continuously changing as in device a Transformer. Figure 22, it will produce a current that changes with time. This changing current in the center coil will produce similar currents in both of the end coils. Voltage Iron Core –V Generator Since the bottom coil has twice the number of turns (twice the magnetic linkage), the voltage across this i Opposite coil will be twice the generator voltage. The power in i Voltage an electronic device is equal to the voltage across N Turns the device times the current through the device (P=VI). If the voltage doubles on the bottom winding, then the current must become 1/2 due to Direction of ½i Core Magnet the law of conservation of power (Power cannot be Rotation Due created or destroyed, but can be transformed from to Current i 2N Turns one state to another). Since the bottom coil is 2V wound in the same direction as the generator coil, the voltage across the coil (top wire to bottom wire) will be the same polarity as the generator voltage. Figure 22 The top coil is wound in the opposite direction -14-
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INDUCTORS TWO MORE LAWS ABOUT INDUCTORS THE Q FACTOR IN COILS X L r Faraday’s Law states that any time a conductor The Q (figure of merit) of a coil is the ratio of the moves through a magnetic field (Figure 23) a inductive reactance to the internal series resistance voltage is generated. Because of this principle, it is of the coil. Since the reactance and resistance can possible to attach a magnet (or coil) to a rotating both change with frequency, Q must be measured at device and produce large amounts of electrical the desired frequency. Anything that will raise the power (the Hoover Dam for example). inductance without raising the series resistance will increase the Q of the coil; for example, using an iron Lenz’ Law states that the induced currents in a core. Lowering the series resistance without conductor passing through a magnetic field will lowering the inductance will also raise the Q, more produce a magnetic field that will oppose the motion turns of larger wire for example. Q is important when between the magnet and the conductor. To produce the inductor is used in a resonant circuit to block or a large amount of electrical power, a large select desired frequencies. The higher the Q, the mechanical force is required (conservation of tighter the selection of frequencies become. power). SUMMARY Lines of Flux The Inductor prevents current from making any S N sudden changes by producing large opposing voltages. Magnetic coupling can be used to transform voltages and currents, but power must remain the same. Coils and transformers can be Wire used to select frequencies. Motion of Magnet Figure 23 INDUCTANCE SYMBOLS AND MARKINGS Most inductors are custom made to meet the requirements of the purchaser. They are marked to match the specification of the buyer and therefore carry no standard markings. The schematic symbols for coils and transformers are shown in Figure 24. These symbols are the most commonly used to represent fixed coils, variable coils, and transformers. Iron Core Transformer Fixed Coils Variable Coils Figure 24 Tunable Transformer -15-
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INDUCTORS SELF TEST THEORY Circle the letter that best fits the description. 1. The inductor is best described as: 7. When an iron core is placed into the center of a coil, the a) Induced Voltage c) Electrical Storage Device inductance will: b) Long Wire d) Electrical Momentum a) Increase c) Stay the Same b) Decrease 2. When wires in a coil are moved closer together, the inductance will: 8. If voltage in a transformer is stepped down, the current a) Increase c) Stay the Same will: b) Decrease a) Increase c) Must Stay the Same b) Decrease 3. Another word used to represent an inductor: a) Wire c) Transformer 9. When a conductor is moved through a magnetic field: b) Coil d) Conductor a) Power is created c) Magnetic field is reduced 4. If the diameter of a coil is increased, the inductance will: b) A voltage is d) a & c a) Increase c) Stay the Same generated on the wire. b) Decrease 10. The Q factor of a coil is equal to: 5. If the number of turns in a coil is decreased, the a) Wire quality c) Ratio of inductance inductance of that coil will: b) Ratio of reactance to resistance a) Increase c) Stay the Same to resistance b) Decrease 11. If windings on a straight rod are in the same direction, 6. An inductor will block: the induced voltage will have: a) Alternating Voltage c) Alternating Current a) Same amplitude c) Same polarity b) Direct Voltage d) Direct Current b) Different amplitude d) Different polarity 12. An inductor stores energy in its: a) Electric field c) Core b) Magnetic field d) Wires PRACTICE Using the coil supplied, answer the following questions. Is the coil wound on an iron form? Yes ____ No ____ What prevents the wire from shorting? ________________________________________ How many turns are on the coil? _____________________ Example: Using a length of 0.1”, a radius of 0.02”, permeability of 14 for the iron core, and 56 turns, calculate the inductance of the coil and record here: ________________________ EXTRA CREDIT 10mH 20mH What happens to the total inductance if you connect two coils as shown in Figure 25. Hint, remember the coiled ? mH hose analogy and try to calculate equivalent if one coiled hose. Figure 25 -16-
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SEMICONDUCTORS THE DIODE, what is it? THE TRANSISTOR, what is it? The diode can be compared to the check valve The transistor is best described as a device that shown in Figure 26. The basic function of a check uses a small amount of current to control a large valve is to allow water to flow in only one direction. amount of current (Current Amplifier). Consider a Once the force of the spring is exceeded, the plate device fabricated as shown in Figure 28. A small moves away from the stop allowing water to pass amount of “Base Current” pushes on the L portion 1 through the pipe. A flow of water in the opposite of the lever arm forcing check valve D to open, 1 direction is blocked by the solid stop and plate. If it even though it is “reverse biased” (pressure is in took a pressure of 0.7lb to exceed the spring force, direction to keep check valve shut). Keep in mind the flow of water versus pressure might look like the base current would not start to flow until the Figure 27. In electronics, this curve would represent check valve D allowed current to flow (0.7lb). If the 2 the typical silicon diode if pounds per square inch current ratio through D and Base was equal to the 1 equaled volts and gallons per minute equaled lever arm advantage, then I / I = L / L . Call this 1 b 1 2 amperes. Of course, the amount of current that flows ratio Beta (b) and let L = 1 inch and L = 0.01 inch. 1 2 through the diode must be limited or the device could Then b = 100 and I will be 100 times I . Since both 1 b be damaged. Just as too much water through the currents must pass through D , I = I + I . These 2 2 1 b check valve could destroy the plate (shorted diode). same principles apply to a silicon NPN transistor. I 1 If the diode is made of Gallium Arsenide, it would becomes collector current (I ), and I would be C 2 take approximately twice the voltage to produce a emitter current (I ). b = I / I and I = I + I . E C B E B C flow of current (spring in Figure 26 is twice as strong). The energy level required to “turn on” a Gallium Arsenide diode is so high, that light is generated when current starts to flow. These diodes are called “Light Emitting Diodes”, or simply LEDs. I1 D1 Water-tight Pivot Pivot L2 Spring Base Current L Lever Solid Stop I 1 Arm b Movable Plate Figure 26 NPN Transistor D2 I2 Figure 28 Current (gals. per min.) 0.7 Pressure (lbs per square inch) Figure 27 -17-
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SEMICONDUCTORS THE PNP TRANSISTOR Figure 29 represents the water pipe equivalent of a Since there are no check valves, the current can PNP transistor. The emitter releases current that flow in either direction. In other words, this device splits into two paths. The base current “forces open” acts like a variable resistor. The Field Effect the collector check valve which collects all the Transistor (FET) also controls current between current except the small amount that goes into the source and drain by “pinching off” the path between base. The direction of current in the PNP transistor them. The level of voltage on the gate controls the is opposite that of the NPN transistor. Because of amount of current that will flow. Since no DC current these differences, the emitter of the PNP is usually flows in or out of the gate (only momentarily a small referenced to the power supply voltage and the amount will flow to adjust to new pressures as in a emitter of the NPN is usually referenced to ground capacitor), the power used by the gate is very close or zero voltage. In both transistors, the current to zero. Remember, power equals voltage times amplification factor (I /I ) is called Beta (b). current, and if the current is zero, the power is zero. c b This is why FETs are used in the probes of test equipment. They will not disturb the circuit being tested by removing power during a measurement. When a second gate section is added (pipe and Emitter rubber) between the source and drain it is called a Dual Gate FET. In our water pipe analogy of the FET IE transistor, the rubber must be very thin and flexible in order to “pinch off” the current from the source to the drain. This means it could be easily damaged by a small “spike” of high pressure. The same is true of IB an electronic FET. A high voltage “spike” (Static Electricity) can destroy the gate and ruin the FET. To protect the FET, they are sometimes packaged with Base metal rings shorting their leads, and a fourth lead may be added to the metal case containing the transistor. I = I + I IC E B C PNP Transistor Source Collector Figure 29 THE FIELD EFFECT TRANSISTOR Gate In Figure 30 the center of a small section of a pipe is made of thin, flexible rubber and that rubber is surrounded by water from a third pipe called the gate. When pressure is applied to the gate, the rubber pinches off the current from the source to the Drain FET Transistor drain. No current flows from gate to drain or source. This device uses a change in gate pressure to control the current flowing from source to drain. Figure 30 -18-
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SEMICONDUCTORS THE INTEGRATED CIRCUIT If the water pipe analogies of the resistor, diode, on a piece of silicon no larger than the head of a pin. transistor, and very small capacitors could be Photographic reduction techniques are used to etched into a single block of steel you would have generate the masking needed to isolate each part. the equivalent of the Integrated Circuit in These masks are then stepped and repeated in Electronics. Figure 31 represents such a device. order to make many separate integrated circuits at This block of steel would have to be very large to the same time on a single substrate. Using mass include all the mechanical parts needed. In production techniques, these circuits are electronics, the actual size of a diode or transistor is manufactured, packaged, and sold at prices much extremely small. In fact, millions can be fabricated lower than the equivalent discreet circuit would cost. 8 The Integrated Circuit 7 14 1 Figure 31 SEMICONDUCTOR SYMBOLS Figure 32 shows the common symbols used in electronics to represent the basic components. Integrated Circuits are usually drawn as blocks with leads or as a triangle for operational amplifiers. The Zener diode (voltage reference diode) is used in the reverse direction at the point of breakdown. Diode LED Zener PNP NPN FET Diode Figure 32 -19-
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