Develop a "feel" for electronics - Page 1
Forum section: electronics / beginners

author: PerranOak
author_rank: Frequent Contributor
timestamp: January 31, 2016, 04:52:05 pm
content: I am determined to learn electronics from the ground up and to be completely familiar with all the concepts.It understand all the maths but it still doesn't give me a real "feel" for the concepts.One writer I came across talked about thinking of the capacitors in a circuit as actually rising and falling (in space!) as a way of intuitively understanding what's occurring.This is the kind of intuitive feel tha tI want to have.Does anyone have suggestions as to books/authors/resources that could help here please?Cheers.

author: Gyro
author_rank: Super Contributor
timestamp: January 31, 2016, 05:21:06 pm
content: That sort of 'feel' comes from experience... and maybe to some small extent, just ability to visualize that way. From what I've observed some engineers never 'get it'.The legendary Bob Pease maintained that the best way to understand things was to fix them when they broke. His book 'Troubleshooting Analog Circuits' is very readable and full of tips and lesser known wisdom on components and circuit behavior.

author: IconicPCB
author_rank: Super Contributor
timestamp: January 31, 2016, 09:52:41 pm
content: Do not resort to a wet finger... might end up with more than a "feel"

author: miguelvp
author_rank: Super Contributor
timestamp: January 31, 2016, 10:08:42 pm
content: There is always the Hydraulic analogy:https://en.wikipedia.org/wiki/Hydraulic_analogy

author: tggzzz
author_rank: Super Contributor
timestamp: January 31, 2016, 11:09:15 pm
content: There are very very very few people that understand all the concepts. E.g. I have heard of one person that was authoratative on radar systems from the antenna through RF front end through signal processing to cockpit human factors, but I never met them!The best technique is to pick a project, understand what are the important theoretical concepts and equations, then build it antest it to see where theory and practice do and don't match. Change some aspect of the design and predict the change in performance, and measure it again.Then repeat with a different project.

author: uncle_bob
author_rank: Unknown
timestamp: February 01, 2016, 01:02:48 am
content: HiNo two people ever learn things in the same way. Most Electrical Engineering is the application of established principles. Physics is the study of those principles. Applied Physics is the boundary between theoretical physics and the more engineering oriented end of things.Each discipline is has it's own emphasis and it's blind spots. You can easily take the "routine" of any one of those areas and befuddle the practitioners in one of the other areas.By far the best way to "get" this stuff in the fashion you are talking about is in a college or university setting. Quite possibly with a dual major.That said, a far more practical way to "get it" is to build stuff and see what happens. Analyze the result and try again. You will have big gaps in your understanding. That's just something you will have to live with.Bob

author: f5r5e5d
author_rank: Frequent Contributor
timestamp: February 01, 2016, 07:00:41 am
content: resistors, caps, ect. are fairly inscrutable to the naked eyeball (when working, not exploding) - so really you are developing mental modeling and model testing skills to guess where to put probe of multimeter or oscilloscope and then interpret what you're seeing on them means for you understanding of the circuit, mental modelschematic reading is critical - there are commonly occurring subcircuits that you grow to recognize, quickly categorize at a "circuit function" levelfor quickly getting started with circuit understanding don't forget simulation - various free and commercial Spice derived circuit simulators with schematic entry gui and waveform viewers can help learn - of course some of the learning is about the sim sw, model limitations, program syntax...but the ability to quickly change the circuit or part values, move, add probes and learn the waveform interpretation can give a big boost over just working on real world circuit aloneand as the math ramps up the software for that can help too Computer Algebra Systems, Numerical/Matrix Solvers - some useful free versions there too - but for Symbolic CAS the best paid versions are way ahead of any free ones I've tried

author: rs20
author_rank: Super Contributor
timestamp: February 01, 2016, 07:06:19 am
content: For me, the hydraulic analogy got me started. I'm not thinking about water anymore, but I still think about the electricity flowing around. But, as mentioned, everyone learns differently, you just have to learn using whatever resources help you understand best, and the intuition might follow.

author: PerranOak
author_rank: Frequent Contributor
timestamp: February 01, 2016, 01:27:38 pm
content: Thank you all for the feedback.I did use the hydro-analogy and this helped. However, I'm in a "mid-phase" where I think I get all that but have not yet progressed to the stage where I can view sub-circuits like sub-routines in a programme.For example, I get the hydro idea about a capacitor but when there's talk of grounding one lead of the capacitor which makes the other lead drop to -Vcc and all that, I get lost! Another thing I can't get over (I think this is a physics vs engineering issue as mentioned) is the idea that current flow "creates" a voltage drop! This is talked of all over but I just can't "feel" it. I can only think of a potential difference creating a current not that a current magically flows then poof! a voltage is thereby created!Maybe it's true that I am theorising too much and experimenting too little.

author: rs20
author_rank: Super Contributor
timestamp: February 01, 2016, 01:37:01 pm
content: Well, if you have a pipe with a partial blockage (resistance), then force water (current) through it, the pressure (voltage) will be higher before the blockage than after. There's a traffic jam behind the blockage, if the pipe bursts, then it would obviously be before the blockage, etc.The water analogy is not always brilliant, especially when there's no current involved. A capacitor tends to hold the relative voltage across its two terminals constant; if terminal A is at 5V at terminal B is at 0V, then terminal B is 5V lower than terminal A. If you set terminal A to 0V, terminal B tends to stay that 5V lower than terminal A, which makes it 5V less than 0V: negative 5V.Having said that, the hydraulic analogy still holds for this case, although really to make that claim I use my knowledge of electronics together with the hydraulic analogy to know that fact about hydraulics, so obviously the analogy is not really helping there!

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 01, 2016, 01:48:14 pm
content: Current flow doesn't "CREATE" a voltage drop. A voltage drop is the RESULT of current flowing through a non-perfect conductor.If you had a 1000 foot extension cord with a large load at the end, you can be sure that you won't see the same voltage out at the load as you started with back at the source. The difference between the source voltage and the voltage out at the end is the "voltage drop".But your "grounding one lead of the capacitor which makes the other lead drop to -Vcc" leaves me scratching my head, also. I have a hard time learning things in the abstract, but can easily see how practical examples work. Do you have an actual circuit where you see this condition?

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 02:04:37 pm
content: I won't get into too many details, but I'll have a go at the two things you've mentioned.1. The capacitor. When a capacitor is charged up and is not in any circuit, there will be a DC voltage across the two terminals, which will tend to stay there (except for leakage - but let's ignore that for the moment and assume we are talking about a high quality one).If you want to measure the voltage, then you have to choose a reference point and measure the voltage with respect to that reference point. For a solitary capacitor, that means picking one of the contacts as the reference point and connecting your meter to that (usually the 'common' or black coloured lead). It is generally assigned a voltage value of 0v because if you put the other lead of your meter on thesamepoint, it's obviously not going to measure anything! Now, having connected the 'common' lead of your meter to this reference point, you then take the other meter lead and touch the other contact of the capacitor - which will give you a reading on your meter of however many volts the capacitor is charged to.BUT is the measured voltage positive or negative? The answer is - it depends on which contact you used as your reference point. Say we have 10v on the capacitor. If you connect the meter common to the negative terminal (using that as the reference point), you will measure the other (positive) contact as being +10v - but if you use the positive terminal as your reference point, then you will measure the other (negative) contact as being -10v.All voltage measurements (not just for capacitors) are measuredwith respect toa particular reference point. (Often this is 'ground' or 'chassis' - but not always.)2. Creating a voltage drop. In one sense - this is stating the process a bit 'back to front'. First you have to remember, there has to be a potential difference (voltage) from a supply (of whatever sort) for any current to flow. Once you have a circuit that connects across this potential difference, the voltage around the circuit has to go from the highest voltage of the supply to the lowest voltage of the supply - so, in fact, those 'voltage drops' are already going to happen - just exactly where and how much they will be across each component in the circuit is the fun bit!Lets take a simple case: a resistor. A voltage drop 'appears' across it when a current passes through it. (How much is defined by Ohm's law: V=IR.) I think 'appears' is a better word than 'create' in this context for understanding - but electrical designers have a pretty firm grip on this stuff and might use the word 'create' - because that's what they meant to happen.

author: retrolefty
author_rank: Super Contributor
timestamp: February 01, 2016, 02:16:30 pm
content: QuoteAnalogies can be very useful, however everyone's head is wired differently so you have to find what works for you. For capacitance I use the analogy in physics of a spring, a thing that can charge or discharge energy.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: February 01, 2016, 10:32:38 pm
content: Quote from: PerranOak on February 01, 2016, 01:27:38 pmWhich analogy are you using? I prefer to think of a capacitor as a stretchy diaphragm in the pipe. A pressure difference will flex the diaphragm until the force of the diaphragm pushing back matches the pressure applied to it. I find this model has a lot in common with real capacitors (like water doesn't need to pass through the membrane for current to flow) and can even have the various real parasitics added to it.So if you take a capacitor like that, and charge it up, you've now stored energy in the diaphragm which will exist even out of circuit (with the ends sealed, obviously.) You could measure the pressure difference between the two sides. If you now attach the high pressure side of the capacitor to your circuit's "0" pressure point, the low pressure side will still be "sucking" and create an even lower pressure region than "0". The capacitor isn't "dropping" voltage, the negative plate is at a lower potential.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: February 01, 2016, 11:04:51 pm
content: Quote from: f5r5e5d on February 01, 2016, 07:00:41 amThis is a place I'm currently struggling. I know the components well enough that I can figure a circuit out eventually, but something like the circuits inside a LM399 (bottom of page 6 on thedatasheet) are prohibitively slow to understand. I even know what the reference section does, which should make it easier!Are there common ways to facilitate building that mental pattern recognition? I feel like I want a desk calendar with a schematic a day to read.

author: rs20
author_rank: Super Contributor
timestamp: February 01, 2016, 11:24:24 pm
content: Quote from: Richard Crowley on February 01, 2016, 01:48:14 pm

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 02, 2016, 01:03:07 am
content: Ah, so you are talking about a voltage inverter circuit.It is the design of the ENTIRE CIRCUIT that produces a negative voltage.The simple connection of the 100 uF capacitor to ground does not "make the other lead drop to -Vcc"It takes the other parts of the output circuit (the two diodes and the 22 uF capacitor also) to accomplish the inversion. And the 555 is used only to generate an alternating (AC) signal.Did you read the description on the page?http://pencho.my.contact.bg/start/comp/555/scheme/555.htm

author: PerranOak
author_rank: Frequent Contributor
timestamp: February 02, 2016, 05:56:21 pm
content: Thanks all, this is very useful.As I begin a new area of "study" I like to develop a feel, an intuition really. Physical analogies, water, diaphragms, etc. are great.Trouble is, I don't know when to let go - I tried to visualise a complex amplifier circuit as water flows, etc.!However, I suspect that I have skipped or misunderstood some things. For example, a BJT current mirror: I can see how the current setting side works, I can see how the varying load side works but how does the first side transmit the "information" to the second side? Is it the small increase in base voltage - this varies very little from the 0.6-0.7V as both BJTs (npn) have grounded emitters. I'm definitely missing something!It could be to do with this current-to-voltage and voltage-to-current converter idea. To me, this sounds like converting apples to oranges!

author: TimFox
author_rank: Super Contributor
timestamp: February 02, 2016, 08:51:32 pm
content: Two elementary concepts I learned in day 1 of my first electronics course:1. The voltage across a capacitor cannot change instantaneously.2. The current through an inductor cannot change instantaneously.This can give a feel for the function of capacitors and inductors, before one calculates more realistic cases with finite rates of change or sinusoidal variation.

author: rs20
author_rank: Super Contributor
timestamp: February 02, 2016, 09:31:02 pm
content: Quote from: PerranOak on February 02, 2016, 05:56:21 pmYes. This is why the two NPNs must be well-matched, and why they are sometimes thermally bonded together.

author: IconicPCB
author_rank: Super Contributor
timestamp: February 02, 2016, 09:46:10 pm
content: At the risk of bursting your bubble ( to use a water analogy) the feel comes from understanding.. understanding comes from studystudy results in knowledge and the knowledge need s to become CRYSTALISED KNOWLEDGE.Crystalised knwoledge is that knowledge which is the kind of knowledge possesed when quized about times tables.. you know 7 x 7 =49 kind of knowledge.This means understanding the maths behind the physics and then compressing that knowledge into the "gut feel" kind of understanding.So comit yourself to improving your theoretical knowledge. Let it become second nature and You to will have visions akin to Tesla's.

author: orolo
author_rank: Frequent Contributor
timestamp: February 02, 2016, 10:17:55 pm
content: In order to learn, you must burn. Start small: resistors, caps, LEDs... passives offer little resistance (to the right voltage). Then graduate to actives: zap MOSFETs, crack JFETs, puncture BJTs, make SCRs explode, watch tubes implode. But don't get lost in the discrete jungle: while frying a tunnel diode, or any other member of a dying race, is an enlightening experience, even the the most purist gourmet indulges in a good MCU bricking from time to time. The moment you sit there, watching the smoke come out of some precious multibuck IC, you'll start to feel it. Burn your way up the food chain. By the time you burn your first 'scope, you'll most definitely feel it. BURN.Just be careful, and don't burn yourself (or others) too much. Safety first.

author: Kilrah
author_rank: Unknown
timestamp: February 02, 2016, 10:21:46 pm
content: Quote from: IconicPCB on February 02, 2016, 09:46:10 pmNot sure that's a compliment, since from the references I have while he was clever in many ways he also seemed to lack the most basic understanding in fields that were extremely important to his endeavors, which caused all the trouble he had during his life...

author: cobbler
author_rank: Unknown
timestamp: February 02, 2016, 11:10:17 pm
content: Quote from: Richard Crowley on February 01, 2016, 01:48:14 pmThe side affect of a voltage drop is always heat of some sort, is that correct?

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 02, 2016, 11:29:02 pm
content: Not quite. Look at ideal capacitors and inductors as an example. They don't dissipate the energy but store it so there is a voltage drop yet no net heat generation.In real capacitors and inductors there is a small resistance however.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2016, 01:56:09 am
content: Quote from: cobbler on February 02, 2016, 11:10:17 pmNot strictly correct.A loss of energy will almost always result in generating heat - but as long as the energy remains within the system, heat does not necessarily get created.When current flows through a resistor, there is no means for the energy to be kept within the system (the resistor) and it will heat up. However, capacitors can store energy in an electric field and inductors can store energy in a magnetic field, so heat isn't an immediate issue.The real world is a little more complex and the lines might seem to blur a bit when you start working with actual components.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 03, 2016, 03:43:15 am
content: Quote from: PerranOak on January 31, 2016, 04:52:05 pmGo back to square one!Get to know your way around resistive circuits first.Learn Ohm's Law,---think about it as a real thing,not as just some "Maths".Try to visualise what is happening.Learn Kirchoff's Law---try to analyse circuits using it.Capacitors:-Capacitors almost always need to be explained using models which are not necessarily correct,but do to get the idea over.This is how I learnt:-WARNING! WARNING!-refers to Electron Flow--EEs may want to turn away,now.Initially,a capacitor has no charge but it does have a few free electrons on its plates.When it is connected to a battery,free electrons at the positive connected plate are attracted to the positive batt terminal.Current flows until that plate is at the same potential as the positive batt terminal.It now appears positive with respect to the other plate.This sets up an electric field between the plates.Free electrons in the negative plate are attracted by the positive plate's potential,but cannot flow through the dielectric,& mass at the plate surface as close as they can get to the source of attraction,robbing the rest of the plate of free electrons.This looks like a positive charge to the batt negative terminal & current flows until the capacitor negative plate & the batt terminal are at the same potential .The capacitor is now "charged".AC current through capacitors is simply a series of charge/discharge cycles.This description is better with a blackboard & diagrams,plus it is simplified to help people get a working understanding of how the things work.It doesn't happen in nice steps like in the above but simultaneously.Also,"free electrons" is a bit of a simplification for "electrons which may be readily dislodged from their associated atoms".The "Electric Field" in the dielectric is shown in various ways in different diagrams.You can chase these up later,but right now,this model makes a lot more sense than hydraulics & diaphragms.

author: miguelvp
author_rank: Super Contributor
timestamp: February 03, 2016, 04:10:44 am
content: The floating capacitors above Chicago just dumped a lot of rain and some lightning

author: free_electron
author_rank: Super Contributor
timestamp: February 03, 2016, 05:04:33 am
content: Quote from: retrolefty on February 01, 2016, 02:16:30 pma capacitor is a big tube blocked in the middle by a balloon. pump wate rint he tube and it will squeeze the balloon flat. release and the pressure int he balloon will expand forcing the water back out. apply too much pressure and the baloon bursts. just like a real capacitor : the dielectric shorts out.

author: dom0
author_rank: Super Contributor
timestamp: February 03, 2016, 12:39:41 pm
content: Quote from: PerranOak on February 02, 2016, 05:56:21 pmAlmost all amplifier circuits and all translinear circuits (like a current mirror) cannot be understood when thinking of bipolar transistors as current-controlled devices. To understand them as voltage-controlled devices (with anecessary, though wildly variable, base current) is not only necessary for understanding many circuits, but is also physically way more accurate (consider a switching application as a simple example).One of the biggest mistakes in text books and other introductory texts to transistors is that they tend to state something like "Well, guys, a bipolar transistor has three terminals, base, emitter, collector, and the base current controls the collector current. Well, okay, that's a simplification, we'll see a better model on slide 1814".--Re. specifically the current mirror. Q1, the input transistor, Q2, the output transistors. Q1 base-collector shorted, hence Q1 develops a Ube exponentially related to the input current (=> Shockley's equation). The emitters of Q1 and Q2 are tied together, as well as the bases are tied together. Hence the Ube of Q2 is identical to the Ube of Q1, hence the emitter currents are identical.(This description disregards all errors and is only meant for a first understanding of the circuit)

author: MrSlack
author_rank: Frequent Contributor
timestamp: February 03, 2016, 02:23:43 pm
content: Very true.ARRL Expermental Methods in RF Design has a good chapter on transistor and amplifier models that isn't bad. I learned how it all works from the predecessor of that book: Solid State Design for the Radio Amateur. Even Art of Electronics beats around the bush a bit too much on this front.That book and blowing up lots of rather expensive gold leaded Motorola 2n2222's was how I worked it out. It's the same way I learned to ride a bike: do it by riding around in circles on on concrete. I was too scared to fall off due to the consequences

author: PerranOak
author_rank: Frequent Contributor
timestamp: February 03, 2016, 03:00:44 pm
content: Thanks again all.Part of my problem is this voltage to current conversion.I've become confused by the BJT being a "current amplifier" or being a "voltage controlled device", dom0. I suppose it's easy to think of the base current being amplified bybetato give the emitter current. As base current increases so does emitter current as the BJT turns on more. So, to think of it as a voltage device means that the base voltage (Vb or Vbe?) must increase to turn it on more. BUT they always quote Vbe as 0.7V-ish (an attribute of the BJT itself) so this can't increase therefore it must mean Vb, yes? BUT Vb increase relative to what?Another thing is that I imagine a sinusoidal signal at the base of a BJT causing a larger signal at the collector. However, this only seems to occur because the BJT changes its resistance with the input - input rises, resistance lowers - so, as the resistance of the BJT falls it is like a voltage divider with less of a "share" of the Vcc and so the output signal falls. Is this right?I did burn a 2N2222 and blew the fuse in my DMM - I learned that current mirrors don't work so well with saturated BJTs!

author: tggzzz
author_rank: Super Contributor
timestamp: February 03, 2016, 03:35:05 pm
content: Quote from: PerranOak on February 03, 2016, 03:00:44 pmYou need to be a little more precise in your thinking; good quality textbooks would be a starting point.For this topic you need to find the equations relating current and voltage in semiconductor junctions (look for the exponential), the relationship between ICIBand IE, and the difference between "large signal" and "small signal" models.Good explanations take a lot of time and work. I certainly don't have time to regurgitatebadexplanations!

author: dom0
author_rank: Super Contributor
timestamp: February 03, 2016, 04:20:01 pm
content: The thing is that Ube <=> Ie ~ Ic is an exponential relationship, so it takes comparatively little change in Ube for a large change in Ie, approximately ~20-25 mV per Iedoubling. Take a look at Shockley's equation.Ube (for the same Ie / Ic) will also have a spread of about 10-50 mV between transistors of the same type and manufacture, and a little more between types.So while Ube in anabsolutesense is a poorly controlled parameter therelativechange of emitter current to base-emitter voltage is well definedover many decades of emitter current.This also explains the need for proper (stable over different transistors, time and temperature) biasing of amplifiers ; using a fixed voltage bias or even a fixed base current bias works well for quick simulations and the like,but never works in practice.Ube <=> Ub: Ube / Vbe means the base-emitter voltage. Ub / Vb sometimes means the same, but sometimes means the base-to-ground voltage ; which one depends on the author, I've seen both.The figure of Ube ~0.65 or 0.7 V is often used in amplifier design for calculating bias points and the like, because at typical currents (couple hundred µA to a few mA) it is close enough, and the figure doesn't need to be accurate - biasing should (see above) not be very sensitive to the exact value of Ube.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: February 03, 2016, 04:20:44 pm
content: To get a feel for electronics, I see two good (among many others ) possibilities- The water analog, as stated above. You can get many examples in "Practical Electronics for Inventors" by Scherz and Monk.- Play with the Everycircuit simulatorhttp://everycircuit.com/https://youtu.be/vcXZylSj9DI

author: orolo
author_rank: Frequent Contributor
timestamp: February 03, 2016, 04:28:16 pm
content: About current mirrors and learning. My experience is that gaining intuition is related to useful paradigms: the hydrodynamic analogy is just a metaphor, it will never fit well enough. A useful paradigm in this case is the translinear principle:https://en.wikipedia.org/wiki/Translinear_circuit. A current mirror is the simplest translinear circuit there is, and translinear loops elegantly capture not only the equal currents in mirrors (multiple mirrors too), but also in unequal mirrors like the ones you will find in voltage references and other ICs. My favorite reference on translinear circuits are the Translinear Lores:http://cas.ee.ic.ac.uk/people/dario/files/E416/translinear-lores.pdf. The translinear paradigm intuitively translates current sharing to diode loops in a circuit. That's an useful insight. You grasp the global paradigm, then reduce the particular cases piecemeal.All the mystery in the current mirror is just a simple application of Kirchof's Voltage Law, the exponential law in diodes, and the astute observation that exponentials turn products into additions. And to assume that the transistors are pretty well matched. With that unifying principle, you can explain some pretty hairy circuits with great ease.The fact that Vbe in an active transistor is almost alwaysabout0.7V is also a consequence of the exponential law. If the base current Ib = Is*exp(Vbe/Vt), then Vbe = Vt * ln(Ib / Is), so you need to square the input current into a transistor (referred to the leakage current Is, which is well into the nanoamp range) to double a voltage. It is clear that voltage won't change much once it reaches its active value. You would need transistor-burning currents. In other words, Vbe is logarithmic in Ib, and logarithms rise slooow past unity. And unity is in the nanoamp scale for a Si transistor.Getting to know the subtleties of Vbe is key to understand how transistors work. The matter of Vbe temperature dependence is another fundamental concept. To get an intuitive grasp, I found Bob Pease's articles on "What's all this Vbe stuff, anyhow?" (parts 1 and 2) absolutely essential:http://www.ti.com/ww/en/bobpease/assets/www-national-com_rap.pdf, page 113. Pease turns the complex Vbe-temp dependence into something intuitive with a graph and some common sense (not to mention geniality and a lot of hands-on experience). There is also a great article on transistor matching in page 111. And a ton of useful info, the document is a gold mine.Quote from: PerranOak on February 03, 2016, 03:00:44 pmHmm, burning. Anyway, you probably dug up already:http://www-mtl.mit.edu/~jldawson/documents/jldrec13.pdfAdding emitter degeneration adds some feedback and 'matches' the transistors, preventing runaway, at the cost of some compliance. The article also gives an elegant, standalone explanation of the mirror from first principles.