Saturday, 28 January 2012

Everything You Should Have Learned in School…but Probably Didn’t

Electrical Engineering 101 (Third Edition): Everything You Should Have Learned in School…but Probably Didn’t

by Paul McGoldrick

Electrical Engineering 101 (Third Edition): Everything You Should Have Learned in School… but Probably Didn’t
by Darren Ashby, Published by Newnes (Elsevier)
ISBN 13: 978-0-12-386001-9, paperback, 291 pp, $34.95, September 2011

Darren Ashby is the Electronics Product Line Manager at Icon Health & Fitness (Logan, UT), manufacturers and purveyors of fitness machines such as the NordicTrack; he was also one of our EExperts (together with Robert Ashby) at ChipCenter (the massive content of which – and our previous incarnation as EDTN – has totally disappeared under UBM Electronics management) which was the home of my AnalogAvenue. He regards himself as an EE who has become a “pointy haired” boss and looks to his text as a way of giving the reader an “intuitive understanding and the tools to take their electronics education to the next level.” The Third Edition expands considerably over the previous work.
In Chapter 0 (smacks of digital) Ashby seeks to explain what electricity is all about, looking at atoms and electrons, conductors and insulators. He also gives a fairly complicated analogy of energy to work.
Chapter 1 opens with a lesson after my own heart: the importance of units! You can solve any piece of mathematics, but unless the units track to your working you have solved nothing. Going on there is a comparison of electrical components to physical equivalents, such as resistors to friction, inductors to mass, and capacitors to springs. Ashby also introduces a concept he calls intuitive signal analysis which is his way of describing how he looks at a circuit and breaks it down into manageable chunks. That works fine with the majority of progressive circuits but as soon as you incorporate feedback, clamping, and even the self-start circuits you will find in power supplies it becomes too much of a guessing game for such analysis. Ashby puts forward six fundamental equations, which he then details in Chapter 2, Basic Theory: Ohm’s Law, voltage divider rule (still Ohm’s Law, Darren), capacitors impede changes in voltage, inductors impede changes in current, series and parallel resistors (Ohm’s Law, again), and Thevenin’s (sic) theorem. The latter, as he correctly points out, could be replaced with Norton which, as a current model, is much easier for virtually all semiconductor models in ICs, etc when voltage sources can rarely be deemed as ‘clean’ of any impedance considerations.
Chapter 2 also covers capacitors and resistors in series and parallel as well as ac generation, reactances, and the essences of low-pass and high-pass filters. An explanation of magnetic fields is a little confusing as he suggests that current can flow in an incomplete circuit but charges are well covered in capacitive electric fields. Ashby then invites into an understanding of transfer functions including a ‘metric converter’ of Km (sic) to mile and Ohm’s Law which are neat segues into feedback and gain loops.
Partially Conducting Electricity is the subtitle of Chapter 3 (Pieces Parts) with a jump into semiconductors and simple explanations of N (sic) and P (sic) doping. With the characteristics of a diode graphed the author misses the major point of telling the reader which way current conducts – that is which is forward and which is reverse – in the p-n device. We also have a current “flow across” moment in the diode and a couple of “current applied” moments in the extension of two diodes to a transistor’s physical arrangement. He then explains the transistor – both pnp and npn – used as a switch and gets into linear amplifiers, albeit to excuse himself because “setting up linear amplifiers can be a bit of a trick” and that op amp use is better! HFE (sic) variations? Really? Continuing on with FETs Ashby almost offers them as a form of super BJT… A paragraph on PCBs is followed by a “list” of additional parts, which is actually a brief descriptor of a Darlington (no symbol, although it is alluded to), an SCR (part of “the thyristor family” but with no explanation), a Triac, and an IGBT.
Chapter 3 continues into power and heat management issues with device temperatures, heat sinking and the like. There is then a massive jump into The Magical Mysterious Op-Amp which Ashby approaches with a repeated reminder that the inputs to an op amp are high impedance. He treats the device as a summing block with both a ve and a –ve input plus a gain element. That’s fine. He also points out, quite correctly, that the massive open-loop gain does not produce huge voltage swings – because of the limitation of the voltage rail(s) – but doesn’t emphasize how close to the rails the output can get, and why.
Negative feedback is introduced as well in this Chapter with the usual op amp equations and he also briefly looks at positive feedback while only mentioning oscillators. Ashby then spends time on binary numbers and gets into logic gates and truth tables before considerable pages on microprocessor basics, I/Os, and a bunch of oddball stuff allegedly related to µPs: phototransistors, Hall devices, digital encoders, potentiometers (and ratiometers, without using the word), sensors, grounding, LEDs, multiplexing, and incandescent lamps. All are basic – too basic – and digital pots are obvious by their absence.
After sixty-four pages, nearly one-quarter of the book, Chapter 3 comes to an end!
Chapter 4 is entitled The Real World which argues for the analog and digital worlds, without once pointing out that digital is just a special case of analog… The author uses a comparator model as an example of an ADC and then a low-pass filter as an example of a PWM DAC. I dislike this approach, which will only confuse the beginner. I would much prefer to see a conventional amplitude/sampling analysis of the creation of a digital counterpart and then a straightforward voltage resistive ladder, the model of 90% of practical circuits, as the DAC.
The Chapter continues with a look at parts that are imperfect: capacitors, resistors, semiconductors, and voltage sources (Ohm’s Law would have been a good place for that one). There is then a Robust Design section, which is management theoretical rather than engineering practical, and Some of My Favorite Circuits, which are all rather trivial. These are followed by a section of just six pages on power supplies. There are a myriad of expressions here that grate but among them are the use of “signal” to describe a dc voltage, “center tap bridge rectifier” to describe a half-wave arrangement, and using a filter capacitor to make the output less “bumpy” rather than describing the filtering of the ac component. Linear regulators are treated as just blocks but switching regulators are given a good description, albeit without some nice current drawingsto follow along with. Ashby then follows with about eighteen useful, but not terribly practical, pages on dc and ac motors.
Chapter 5 is entitled Tools and spends about the same number of pages on soldering as it does, in total, on test meters, oscilloscopes, logic analyzers, and simulators. The Chapter then continues with People Tools, which is actually a primer on the sales channels for components.
Chapter 6 is Troubleshooting, which consists of essays on component problems, EMI, and bugs in code. Generic but readable.
Touchy-Feely Stuff is the matter of Chapter 7 and consists of further essays on management, employees, interviewing techniques, and the like. Is it relevant to the text? Why not, I suppose. A very incomplete glossary and an index round out the book.
Electrical Engineering 101 is not really about electrical engineering at all. It is about electronics. Is it the best it could be? Absolutely not; there are huge improvements that could be made that would turn the book into a much more solid and useful text: Newnes should have been on top of that editorially before it reached the Third Edition.
I like the Thumb Rules scattered in each section, although some of them are a little too folksy. Ashby also shows an overfondness for understanding the charging characteristic of a capacitor, something he raises multiple times. There is a screaming need in the book to get the balance better and to delve into some real circuits. And, of course, the idea that discrete transistors should be avoided at all costs when op amps are available could drive any sane analog designer screaming mad!
There are many who would find this book to be a useful primer in many ways; there are others who would find it very confusing. It deserves a buying audience but I look forward to a Fourth Edition that is more carefully structured and balanced for the putative designer.

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