电子工程师必知必会.pdf

Newnes is an imprint of Elsevier 30 Corporate Drive, Suite 400 Burlington, MA 01803, USA Linacre House, Jordan Hill Oxford OX2 8DP, UK Copyright 2009, Elsevier Inc. All rights reserved. No part of this publication may be reproduced, stored in a retri system, or transmitted in any or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Permissions may be sought directly from Elsevier’s Science she was encouraging me to drop out when she made her comment. So good luck, read on, and prove me right It ain’t all that hard vii 1 Just a hint, most of the chuckles are in the footnotes, and if you like those, check out the glossary too Preface Preface viii Well, that about says it all. If you do decide to give this book a chance, I want to say thank you, and I hope it brings you success in all you do OVERVIEW For Engineers Granted, there are many good teachers out there and you might have gotten the basics, but time and too many “status reports ” have dulled the fi nish on your basic knowledge set. If you are like me, you have found a few really good books that you often pull off the shelf in a time of need. They usually have a well-written, easy-to-understand explanation of the particular topic you need to apply. I hope this will be one of those books for you. You might also be a fi sh out of water, an ME thrown into the world of electri- cal engineering, and you would really like a basic understanding to work with the EEs around you. If you get a really good understanding of these principles, I guarantee you will surprise at least some of the “ sparkies ” as I like to call them with your intuitive insights into problems at hand. For Students I don’t mean to knock the collegiate educational system, but it seems to me that too often we can pass a class in school with the “assimilate and regurgi- tate ” . You know what I mean Go to class, soak up all the things the teacher wants you to know, take the test, say the right things at the right time, and leave the class without an ounce of applicable knowledge. I think many students are forced into this mode when teachers do not take the time to lay the groundwork for the subject they are covering. Students are so hard-pressed to simply keep up that they do not feel the light bulb go on over their heads or say, “Aha, now I get it ” The reality is, if you leave the class with a fundamental understanding of the topic and you know that topic by heart, you will be emi- nently more successful applying that basic knowledge than anything from the end of the syllabus for that class. For Managers The job of the engineering manager 2 really should have more to it than is depicted by the pointy-haired boss you see in Dilbert cartoons. One thing many 2 Suggested alternate title for this book from reader Travis Hayes EE for Dummies and Those They Manage . I liked it, but I fi gured the pointy-haired types wouldn’t get it. ix managers do not know about engineers is that they welcome truly insightful takes on whatever they might be working on. Please notice I said “truly insight- ful”; you can’t just spout off some acronym you heard in the lunchroom and expect engineers to pay attention. However, if you understand these basics, I am sure there will be times when you will be able to point your engineers in the right direction. You will be happy to keep the project moving forward, and they will gain a new respect for their boss. They might even put away their pointy-haired doll For Teachers Please don’t get me wrong, I don’t mean to say that all teachers are bad; in fact mostof my teachers barring one or two were really good instructors. However, sometimes I think the system is fl awed. Given pressures from the dean to cover X, Y, and Z topics, sometimes the more fundamental X and Y are sacrifi ced just to get to topic Z . I did get a chance to teach a semester at my own alma mater. Some of these chapters are directly from that class. My hope for teachers is to give you another tool that you can use to fl ip the switch on the “Aha” light bulbs over your stu- dents’ heads. For Everyone At the end of each topic discussed in this book are bullet points I like to call Thumb Rules. They are what they seem those “rule-of-thumb” concepts that really good engineers seem to just know. These concepts are what always led them to the right conclusions and solutions to problems. If you get bored with a section, make sure to hit the Thumb Rules anyway. There you will get the dis- tilled core concepts that you really should know. Preface Darren Coy Ashby is a self-described “techno geek with pointy hair. ” He con- siders himself a jack-of-all-trades, master of none. He fi gures his common sense came from his dad and his book sense from his mother. Raised on a farm and graduated from Utah State University seemingly ages ago, Darren has nearly 20 years of experience in the real world as a technician, an engineer, and a manager. He has worked in diverse areas of compliance; production; testing; and, his personal favorite, R however, those ideas were built on a presumption of a cer- tain amount of knowledge. On the other hand, I realized that the knowledge that was to be presented would make more sense if you fi rst understood these conceptsthus my chicken-vs.-egg dilemma. Suffi ce it to say that I jumped ahead to explaining the chicken the chicken being all about using electricity to our benefi t. I was essentially assuming that the reader knew what an egg was the “ egg ” being a grasp on what electricity is. Truth be told, it was a bit of a cheat on my part, 1 and on top of that I never expected the book to be such a runaway success. Turns out there are lots of people out there who want to know more about the magic of this ever-growing electronic world around us. So, for this new and improved edition of the book, I will digress and do my best to explain the “ egg. ” Skip ahead if you have an idea of what it’s all about, 2 or maybe stick around to see if this is an enlightening look at what electricity really is. 1 What Is Electricity Really CHAPTER 0 CHAPTER 0 1 Do we all make compromises in the face of impossible deadlines Are the deadlines only impossible because of our own procrastination Those are both very heavy-duty questions, not unlike that of the chicken-vs.-egg debate. 2 Thus the whole Chapter 0 idea; you can argue that 0 or 1 is the right number to start count- ing with, so pick whichever chapter you want to begin with of these two and have at it. CHAPTER 0 What Is Electricity Really 2 SO WHAT IS ELECTRICITY The electronwhat is it We haven’t ever seen one, but we have found ways to measure a bunch of them. Meters, oscilloscopes, and all sorts of detectors tell us how electrons move and what they do. We have also found ways to make them turn motors, light up light bulbs, and power cell phones, computers, and thousands of other really cool things. What is electricity though Actually, that is a very good question. If you dig deep enough you can fi nd RSPs 3 all over the world who debate this very topic. I have no desire to that join that debate having not attained RSP status yet. So I will tell you the way I see it and think about it so that it makes sense in my head. Since I am just a hick from a small town, I hope that my explanation will make it easier for you to understand as well. THE ATOM We need to begin by learning about a very small particle that is referred to as an atom . A simple representation of one is shown in Figure 0.1 . Atoms 4 are made up of three types of particles protons, neutrons, and elec- trons. Only two of these particles have a feature that we call charge. The proton carries a positive charge and the electron carries a negative charge, whereas the neutron carries no charge at all. The individual protons and neutrons are much more massive than the wee little electron. Although they aren’t the same size, the proton and the electron do carry equal amounts of opposite charge. Now, don’t let the simple circles of my diagram lead you to believe that this is the path that electrons move in. They actually scoot around in a more ener- getic 3D motion that physicists refer to as a shell. There are many types and shapes of shells, but the specifi cs are beyond the scope of this text. You do need to understand that when you dump enough energy into an atom, you can get an electron to pop off and move fancy free. When this happens the rest of the atom has a net positive charge 5 and the electron a net negative charge. 6 Actually they have these charges when they are part of the atom. They simply 3 RSP Really Smart Person. As you will soon learn, I do hope to get an acronym or two into everyday vernacular for the common engineer. BTW, I believe that many engineers are RSPs; it seems to be a common trait among people of that profession. 4 The atom is really, really small. We can sorta “ see ” an atom these days with some pretty cool instruments, but it is kinda like the way a blind person “ sees ” Braille by feeling it. 5 An atom with a net charge is also known as an ion . 6 Often referred to as a free electron. 3 cancel each other out so that when you look at the atom as a whole the net charge is zero. Now, atoms don’t like having electrons missing from their shells, so as soon as another one comes along it will slip into the open slot in that atom’s shell. The amount of energy or work it takes to pop one of these electrons loose depends on the type of atom we are dealing with. When the atom is a good insulator, such as rubber, these electrons are stuck hard in their shells. They aren’t moving for anything. Take a look at the sketch in Figure 0.2 . The Atom Protons Neutrons FIGURE 0.1 Very basic symbol of an atom. FIGURE 0.2 Electrons are “stuck” in these shells in an insulator; they can’t really leave and move fancy free. In an insulator, these electron charges are “ stuck ” in place, orbiting the nucleus of the atomkinda like water frozen in a pipe. 7 Do take note that there are just as many positive charges as there are negative charges. With a good conductor like copper, the electrons in the outer shells of the atoms will pop off at the slightest touch; in metal elements these electrons bounce around from atom to atom so easily that we refer to them as an electron sea, or you might hear them referred to as free electrons. More visuals of this idea are shown in Figure 0.3 . You should note that there are still just as many positive charges as there are negative charges. The difference now is not the number of charges; it is the fact that they can move easily. This time they are like water in the pipe that isn’t fro- zen but liquidalbeit a pipe that is already full of water, so to speak. Getting the electrons to move just requires a little push and away they go. 8 One effect of all these loose electrons is the silvery-shiny appearance that metals have. No wonder that the element that we call silver is one of the best conductors there is. One more thing A very fundamental property of charge is that like charges repel and opposite charges attract. 9 If you bring a free electron next to another free electron, it will tend to push the other electron away from it. Getting the positively charged atoms to move is much more diffi cult; they are stuck in place in virtually all solid materials, but the same thing applies to positive charges as well. 10 FIGURE 0.3 An electron sea. 7 I like the frozen water analogy; just don’t take it too far and think you just need to melt them to get them to move 8 Analogies are a great way to understand something, but you have to take care not to take them too far. In this case take note that you can’t simply tip your wire up and get the elec- trons to fall out, so it isn’t exactly like water in a pipe. 9 It strikes me that this is somewhat fundamental to human relationships. “ Good ” girls are often attracted to “ bad ” boys, and many other analogies that come to mind. 10 There are defi nitely cases where you can move positive charges around. In fact, it often happens when you feel a shock. It’s just that most of the types of materials, circuits, and so on that we deal with in electronics are about moving the tiny, super-small, commonly easy-to-move electron. For that other cool stuff, I suggest you fi nd a good book on electro- magnetic physics. CHAPTER 0 What Is Electricity Really 4 NOW WHAT So now we have an idea of what insulators and conductors are and how they relate to electrons and atoms. What is this ination good for, and why do we care Let’s focus on these charges and see what happens when we get them to move around. First, let’s get these charges to move to a place and stay there. To do this we’ll take advantage of the cool effect that these charges have on each other, which we discussed earlier. Remember, opposite charges attract, whereas the same charges repel. There is a cool, mysterious, magical fi eld around these charges. We call it the electrostatic fi eld. This is the very same fi eld that creates everything from static cling to lightning bolts. Have you ever rubbed a balloon on your head and stuck it on the wall If so you have seen a demonstration of an elec- trostatic fi eld. If you took that a little further and waved the balloon closely over the hair on your arm, you might notice how the hairs would track the movement of the balloon. The action of rubbing the balloon caused your head to end up with a net total charge on it and the opposite charge on the balloon. The act of rubbing these materials together 11 caused some electrons to move from one surface to the other, charging both your head and the balloon. This electrostatic fi eld can rt a force on other things with charges. Think about it for a moment If we could fi gure out a way to put some charges on one end of our conductor, that would push the like charges away and in so doing cause those charges to move. Thumb Rules Electricity is fundamentally charges, both positive and negative. Energy is work. There are just as many positive as negative charges in both a conductor and an insulator. In a good conductor, the electrons move easily, like liquid water. In a good insulator, the electrons are stuck in place, like frozen water but not exactly; they don’t “ melt ” . Like charges repel and opposite charges attract. 11 Fun side note Google this balloon-rubbing experiment and see what charge is where. Also research the fact that this happens more readily with certain materials than others. Now