Textbook vs. reality: voltages. - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: March 10, 2023, 08:49:49 pm
content: Often I see the "high level" tutorial view of a circuit or concept, like a mosfet driver, JBT circuit, buck, boost, zenner or whatever standard building block and I understand it. Usually I measure the same thing they do and sort of understand why.Then I try it in practice and I get whacky results. It's not even things like "it says" you should have 0.1V and I have 0.15V. I'm talking about where you expect 5V and get 2.6V. When you expect a 0V and get a 0.5V.Example. Testing an NPN to pull a high side P Mosfet on a 12V rail to ground from a 3.3V rail device. It worked. But the voltages were baffling. The output was pulsing with the PWM signal on the gate perfectly, nice rise time, slightly "capacitve" fall time, but appeared offset by about 2.9V. Even when I stopped the current flow and turned the mosfet fully off... it read 2.9V. Only if I shorted the 100nF cap on the output did it read 0V.It was only then it twigged. I swapped the white LED with a forward voltage of 2.9V for a resistor and bingo. The output was pulsing at the input PWM from 0V to Vcc. Trying different loads produced a variety of results, as did varying the frequency and the capacitance.I suppose it's the same as in software engineering, simple concepts are simple. Simple concepts expressed within complex frameworks with other components are not.

author: Benta
author_rank: Super Contributor
timestamp: March 10, 2023, 09:03:10 pm
content: This has absolutely nothing to do with "Textbook vs. Reality".But it has everything to do with you doing an incomplete/erroneous circuit analysis.

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2023, 09:08:44 pm
content: Yup.I'll add that all models areand have to besimplifications of the real world. It isnecessaryto understand the boundaries within which the simplifications produceusefulresults.Examples: capacitors, resistors, inductors, wires are all simplified models of these real world with significant limitations.

author: exe
author_rank: Unknown
timestamp: March 10, 2023, 09:37:29 pm
content: Without schematics it's hard to understand the problem.Anyway, there are certain topics that are often oversimplified in textbooks. For a skilled engineer it's important to understand that real components have tolerances and drifts. I usually look at multiple sources of information to better understand the topic.

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2023, 09:42:37 pm
content: Worse: there is no such thing - and can never be such a thing - as a capacitor or resistor, and ground/earth is a fiction.

author: james_s
author_rank: Super Contributor
timestamp: March 10, 2023, 09:55:29 pm
content: Quote from: tggzzz on March 10, 2023, 09:42:37 pmI don't think that's helpful to a beginner, it's only going to add confusion.There are certainly things we call capacitors and resistors, and ground and earth are valid concepts, nothing in the real world is ideal but that doesn't make it fiction.

author: tggzzz
author_rank: Super Contributor
timestamp: March 10, 2023, 10:16:03 pm
content: Quote from: james_s on March 10, 2023, 09:55:29 pmReal world physical capacitors have length. That means they also have inductance. That leads to some SMD capacitors being 0306 rather (cf 0603), and having a self-resonant frequency. Even beginners ignore that at their peril.What is the capacitance of an MLCC capacitor at 5Vdc and 0Vdc? Surely they should be the same.How do real work capacitors "magically" increase the voltage across their terminals while they are disconnected? Dielectric absorption? What's that?If ground/earth having the same potential everywhere is valid, please explain why those caught out in a thunderstorm are told to keep their feet together rather than apart. There are many other examples!Models are a useful simplification,within limits. The limits are important and must be understood!

author: paulca
author_rank: Super Contributor
timestamp: March 10, 2023, 10:50:21 pm
content: Another recent realisation.Current. Input current == output current (if vin==vout). However the current flowing between components may need to be far, far higher, orders of magnitude higher.Just because your circuit consumes 50mW and 20mA doesn't mean the track between an inductor and a capacitor won't "be capable" or fully using 1000Amps if you give it to it enough track. Often those simple details are the major impacts. They just aren't covered in tutorials which tend to focus too heavily on examples.

author: paulca
author_rank: Super Contributor
timestamp: March 10, 2023, 10:55:26 pm
content: Obviously the main issue is I'm a software engineer trying to do electronics.I'm an

author: TimFox
author_rank: Super Contributor
timestamp: March 10, 2023, 11:13:06 pm
content: Quote from: james_s on March 10, 2023, 09:55:29 pmObviously, when learning electronic circuit theory, the student starts with resistance, capacitance, etc. to study how circuits work.Later, one needs to know the properties of physically obtainable resistors, capacitors, etc. to improve his understanding of how real circuits work.Eventually, he learns that "ground" is not a good concept, and should be replaced by a more accurate word (depending on the context) such as "PE", "circuit common", "ground plane", etc.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 12, 2023, 05:45:18 pm
content: OMG, a software engineer trying to do electronics.Thats nearly as bad as gamer trying to do web design!There's no Ctrl+Z or backspace on the bench so you have to think before you act.

author: exe
author_rank: Unknown
timestamp: March 12, 2023, 05:57:02 pm
content: I hope some posts here are jokes and not people showing their inflated egos.

author: golden_labels
author_rank: Super Contributor
timestamp: March 12, 2023, 11:02:46 pm
content: Quote from: paulca on March 10, 2023, 08:49:49 pmFor breadboard circuits always check connections. They are unreliable and can easily introduce unexpected few kiloohms or capacitive coupling, where a direct connection was expected. The connection may even be present or missing only during measurement, yielding inconsistent results.If the circuit is right, you might have forget to account for inaccuracies. A modern resistor will be 5% or 1% tolerance, though in reality it will be far better than this. But a common jellybean BJT may have current gain varying by half an order of magnitude straight from factory, and that itself is already a value specified in particular operating conditions. You can’t slap it into an equation and blissfully forget it’s a range, not a single point.Otherwise the answer usually is: you used a wrong model. Tossing a bullet in a classroom and measuring fall distance with respect to time yields a quadratic equation. And this is the equation you see in the textbook. Try firing a bullet straight up into air and you might be very surprised by both the time it takes for it to reach ground and the speed it reaches. Try using textbook equations for sending a rocket to an orbit over Earth and you will be lucky to not see a catastrophic failure on every stage of its jurouney. That is because a different model is needed, accounting for many more factors.Electronic circuits are not different. Textbooks are meant to introduce concepts and general schematics are for conveying ideas. Models used for actual circuits are usually way more complicated. This is where experience comes: being able to spot potential shortcomings of the simpler model, understand their sources and adjust.I do not know the layout in your PWM example (and it is not relevant here), but the intuition already tells me a potential issue. You used a direct current model with ideal switches, expecting two stable situations. But this is an alternating current operation, so AC characteristics of the circuit can’t be ignored. There are capacitances in this circuit, which have to be charged and discharged. Not only it means some frequencies are partially passed where you expect perfect isolation, but charging and discharging takes time, introducing shifts to the signals.For a typical design nobody will calculate those, though, as the exact model would be too complicated. Here is where consulting more experienced people comes: they will tell you, how to adjust the design to simply minimize the influence of unwanted factors.Quote from: exe on March 12, 2023, 05:57:02 pmI have some bad news to you.

author: shapirus
author_rank: Super Contributor
timestamp: March 12, 2023, 11:27:50 pm
content: Quote from: golden_labels on March 12, 2023, 11:02:46 pmWhich sometimes can be considered a good thing. It exaggerates the effects introduced by non-ideal connections and traces and exposes the potential problems which otherwise would remain unnoticed. And then, when they are accounted for on the breadboard, the circuit will (usually) have a greater chance of running reliably and predictably in the finished product.It's like running a C program linked with a malloc debugging library. The program will run slower, but it will crash and give you a stack trace pointing to your mistake where otherwise it would keep running and, maybe, crash later in a bizarre way in an unrelated situation, or not crash, but silently corrupt data, etc.

author: EPAIII
author_rank: Super Contributor
timestamp: March 14, 2023, 07:37:29 am
content: Every part in your circuit has TOLERANCES. Resistors, +/-5%. Capacitors can be as much as +100%/-5%. And active components have "typical" performance factors and curves. Everything can vary from the nominal values. 5% here, 10% there, another 8% somewhere else and if they all go in the same direction, you can have a real serious error.This is why many circuits have things like gain controls. Why analog chip manufacturers will laser trim values on those chips. Etc. It is hard to find electronic components with very tight tolerances and then you pay for that precision.I am not surprised that a circuit made with run-of-the-mill parts and no means of adjusting it would have Voltage differences as much as 5%, 10%, even 25% different from the calculated values.This is not unique to electronics. All areas of real world engineering have tolerances.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 08:13:32 am
content: To repeat. I am not talking about tolerances I'm talking about completely different results. Like the transistor switch example where half your voltage drops across the NPN. When you expect a 0-5V square wave and get a 2.9V to 5V triangle wave.

author: golden_labels
author_rank: Super Contributor
timestamp: March 14, 2023, 09:48:00 am
content: Component tolerancesisone ofthe possible answersto what you are describing, in any more complicated circuit.As for your single, particular case from the last post: postexactschematics,exactpart numbers, and describeexactly: what you are doing, how you are measuring, whereexactlydo you put each probe, under whatexactconditions, feedingexactlywhat toexactlywhich input.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 10:13:20 am
content: In the case of the 2.9V to (what was actually 4.2V), that much I twigged onto. The load was a white LED. When the transistor switched off, the voltage on it's output will pull down to the diode forward voltage it would stop conducting and the transistor emittor is at that point floating in free air.This brings me to the other point you mentioned about exactly how and what with you do the measurement.I had 3 competing measurements all telling me different things.The multimeter said 2.9V.The shunt resistor VBus sense when I added it said 0V.The osciliscope when connected read 5.9V.There wasn't even a >5V source in the system.... except for the scope ground which starting sinking current off the USB leakage. Not a major issue normally, but at that point I stripped the breadboard in disgust.Later. The multimeter has a 10Meg input impedence. It is therefore able to see floating voltages. The VShunt measurement has a load on the line which pulls the floating voltage down. The scope is earthed. My earth referenced stuff is riddled with SMPS leakage and noise.The annoying thing about this, which answer is correct and I'm pretty sure the answer is.... any or all of them, it depends on what question you are asking.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 10:20:57 am
content: I will draw a schematic. It's a project I'm working on that, unfortunately, means I can't avoid the analogue side at it's lower level. All these transistor and buck related experiments have been trying to get a practical understanding of how this stuff works.I know there is a huge amount of theory goes into it, maybe my hobby style engineering doesn't suit electronics. I go for low hanging fruit, try rather than exhaust research and work on the principle that you'll usually get 80% of what you want with 20% the effort. So never do a complete job. Just move the goal posts and do the next 80%.Try the circuit and it works. 5 minutes.Read the high school version, do 3 examples, read the under graduate level version, do 3 examples. Study up on the parameters with an LTSpice model. A week. The circuit still takes 5 minutes to build and test.Unfortnately, what you are telling me is that option 1 comes back to bite you later as it might test fine on it's own, but use it in anger in a real circuit and it will fail and you won't have a clue why. If you took option 2, you would probably immediately know what's gone wrong.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 14, 2023, 10:40:16 am
content: Specific parameters may differ from one part to another, even when they are the same name.For example, a MOSFET can gave different turn-on voltage. We both order the same part number, we both do the same schematic, and in the end we might measure different voltages in practice. This is not textbooks' fault. It's about that specific schematic you described in the OP, and which I only vague understand what the schematic was about.To get any useful comments about the voltage you measured, you have to post the schematic, and to tell where you measured and in what conditions, etc. Often a picture of the physical circuit helps, too. At least an LTspice printscreen + .asc, or the link to the original schematic.Would you be able to debug my program if I only tell you: I made a loop and it doesn't stop at i=10, as in my textbook? I don't post the code, but it's a loop in C, will only take you 5 minutes to write the loop.

author: shapirus
author_rank: Super Contributor
timestamp: March 14, 2023, 10:50:58 am
content: Quote from: paulca on March 14, 2023, 08:13:32 amPerformance curves in the datasheets will usually give you an answer for why this happens.

author: mariush
author_rank: Super Contributor
timestamp: March 14, 2023, 10:55:29 am
content: Quote from: paulca on March 14, 2023, 10:20:57 amA led is not an on/off device . It as an off region where the voltage is much lower than forward voltage, a very narrow region where it's just about to turn on where it behaves like it has a resistor in series with it and consumes very little current, and then a region where it opens up and you have to start limiting the current otherwise it will consume as much current as you give it.If the led had a forward voltage of around 3v to 3.2v, 2.9v may have been just low enough for the led to be in that intermediate region and not conduct a lot of current.A LEDs forward voltage is also affected by its temperature. A cold led will have higher forward voltage, as it warms up the forward voltage needed to turn on the led decreases.Both the very narrow middle region where the led is barely open and the fully on region drift with temperature, usually the forward voltage goes down.So as you can see, a white led is not a basic / perfect "load" for a test circuit. An incandescent bulb maybe, but even that has properties that change as the filament gets up to temperature.A 3v-5v motor, a 8-10w resistor, those would be good enough loads to test with.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 11:00:33 am
content: Quote from: paulca on March 14, 2023, 10:20:57 amOr more accurately...Ifthe circuit works it isthatinstance of a circuit underthosetest conditions.Another instance might not work and if the operating conditions change it might not work. You have no idea of how close to the edge you are.More cynically I'll observe that your approach is typical of those working in the software industry - and that's one reason why software failures are so frequent and intermittent.(My background: I've developed systems and products from low-noise analogue and digital, throuvgh embedded, to web back-ends and telecom systems)

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 11:04:22 am
content: Quote from: mariush on March 14, 2023, 10:55:29 amInductance? Back EMF?

author: shapirus
author_rank: Super Contributor
timestamp: March 14, 2023, 11:05:42 am
content: This discussion isn't going to yield anything useful beyond the "the world is not ideal" statement, unless we see schematic diagrams to discuss what's going wrong or not as expected in each particular case.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 12:08:28 pm
content: I'll get round to the schematic and start a thread on the specifics there.Thanks guys.

author: jonpaul
author_rank: Super Contributor
timestamp: March 14, 2023, 01:41:32 pm
content: schematic..should have been in first postsimulation..GIGO garbage in garbage out...only as,good,as the setup, parameters, assumptions, etc.often easir to just build the circuit than bother with Sims.j

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 02:55:02 pm
content: Quote from: jonpaul on March 14, 2023, 01:41:32 pmSimulations allow easy fast sensitivity analyses, without destroying components.

author: shapirus
author_rank: Super Contributor
timestamp: March 14, 2023, 03:31:11 pm
content: Quote from: tggzzz on March 14, 2023, 02:55:02 pmAs well as checking voltage drop and power dissipation on components, and many more.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 03:35:39 pm
content: Quote from: tggzzz on March 14, 2023, 02:55:02 pmIt has been recommended to me by several people they can be used as calculators to save on the maths. Like if you have a circuit that will operate across a range of parameters, rather than run the full matrix of sums, you can employ Spice and produce all the output as graphs.I found LTSpice a little abnoxious to use and often takes more time and causes more confusion. I suppose like calculator, understanding the maths it's doing helps you use it.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 04:10:59 pm
content: Quote from: paulca on March 14, 2023, 03:35:39 pmNothing can save on the mathematics. Mathematics leads tounderstanding.Simulation can save onarithmetic,confirmthe maths, and verify that the non-linear behaviour of elements does not affect the circuit's operation.LTSpice is indeed quirky, but has some good points. E.g. the schematic is ASCII text, so can be copied and pasted for sharing.It is not the only Spice. The choice between them is cost, features, and most importantly the quality of the models. Relevant aphorism: "all models are wrong, but some are useful".

author: TimFox
author_rank: Super Contributor
timestamp: March 14, 2023, 05:02:24 pm
content: Note that in Spice itself, the ".AC" analysis applied to a passive circuit (R, C, L, sources, but no non-linear devices) is merely doing the algebra and should be exact.Adding non-linear devices to the circuit, ".AC" first finds the quiescent point (as a DC analysis) and then linearizes the circuit for small changes about that point.If you apply 1 V of AC drive to that circuit, you may see 100 V at the output, which is not physical (especially for 15 V DC supply to the circuit): it merely represents that in the linear region the voltage gain is x100.(Therefore, it does not matter to that analysis if your 1 V is rms, peak, or peak-to-peak.)The ".TRAN" analysis should represent actual voltages in the non-linear region of the device operation, but is approximate and can be fooled by incorrect time steps and other practical considerations, since it is a finite-step integration that calculates incremental voltages in incremental times that can lead to numerical errors that propagate through the simulated time range.

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2023, 08:24:46 pm
content: Quote from: tggzzz on March 10, 2023, 09:42:37 pmNo.Resistors and capacitors absolutelydoexist. You can buy them. I've used them here and there, as many people here have.What don't exist in the real world areidealresistors and capacitors, i.e. ones with zero parasitic effects. That's why there exists the established term for those:ideal resistorsandideal capacitors, terms you encounter in textbooks, though it's often implied.Quote from: tggzzz on March 10, 2023, 09:42:37 pmNo, it's not a fiction. It just doesn't mean whatever insanely narrow, rigid definition you've concocted in your brain!

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 08:47:47 pm
content: Quote from: tggzzz on March 10, 2023, 09:42:37 pmIs this ... like... there is no such thing as a triangle or a square?You see this is one of my issues with electronics and discussions like this. It happens in software engineering too. Discussions where the question can be answered in a few brief comments.... end up being disected by the grey beards to the N'th detail and such things as people being reminded that Euclid was a drug addict, Tesla was a few volts over his pack voltage and shit like that... don't help.What beginners need is "What to expect". If you give them the circuit give them the unit test too. Build this, expect this.In fairness that's what a lot of tutorials do for specific examples.Damn. My problem is Maths. It's very odd as a software engineer that I struggle with maths. Yet it's not the logic and operational aspects of maths that allude me, but the language. Electronics and Economics/finance are the two domains which beg and beckon towards the ... what I consider SME or "quantitative engineering" concern in the day job.I am not unique. I have seen code.... (blade runner scene)... I've seen code trying to derive PI effectively from a result set of radian values to validate them. I've seen all manor of things that would absolutely terrify maths teachers which software engineering came up with to solve a problem. I find usually the communication is far too one way. A software engineer can easily create a proof that shows a given set of operations produces a range of values which are "correct" by requirements. The trouble is, it's not expressed in an easy way for the maths person to understand.Mathlab et. al. helps to bridge that communications gap, something I should explore for this forum and electronics in general. Maybe... ChatGPT can go the other way.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 08:53:02 pm
content: Quote from: tooki on March 14, 2023, 08:24:46 pmYou contradict yourself in your next paragraph.QuoteI suggest you start by stating your definition of ground, and where it exists.

author: james_s
author_rank: Super Contributor
timestamp: March 14, 2023, 08:55:50 pm
content: Quote from: paulca on March 14, 2023, 08:47:47 pmEngineers are notoriously pedantic and a few take it to the extreme, so this sort of thing is to be expected.I struggle with math too, always have, but math is such a core principal in engineering that it is impossible to avoid. Every aspect of electrical circuits is described with math.

author: james_s
author_rank: Super Contributor
timestamp: March 14, 2023, 08:59:43 pm
content: Quote from: tggzzz on March 14, 2023, 08:53:02 pmHe hasn't contradicted himself at all. Resistors and capacitors do exist. These are not the same as *ideal* resistors and capacitors. You could call the things you can buy "non-ideal real world resistors that have parasitic components" but that's a bit long winded, most of us know that's what a person means by default when they refer to a resistor. In the real world NOTHING is ideal, it doesn't have to be specified."Ground" is a node in a circuit that has been chosen to which all other measured voltages are referenced to. Most often it is associated with the negative terminal of a battery, the negative side of a single ended power supply or the midpoint of a split supply.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 09:07:30 pm
content: Quote from: james_s on March 14, 2023, 08:55:50 pmGiven that the topic title is "textbook vs reality", noting the differences between theory and practice isn't being pedantic.Most electronic engineering is based around maths that is a vast simplification of Faraday's differential equations. Hence it is only to be expected that even the "everyday" mathematical models and analysis is inexact. Plus the physical devices only match the mathematical models in some circumstances.Appreciating the boundaries of a model is fundamental to engineering. Then you can ensure your design stays well within the boundaries (if at all possible).

author: TimFox
author_rank: Super Contributor
timestamp: March 14, 2023, 09:07:58 pm
content: In my reply #9 above, I carefully stated that one first learns about "resistance" and "capacitance", including the mathematics thereof.Later one learns what else is contained in commercially-available "resistors" and "capacitors", including parasitics and tolerances.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 09:13:39 pm
content: Quote from: james_s on March 14, 2023, 08:59:43 pmHe said you could buy a resistor. No you can't. You can buy a resistor+inductor+capacitor (to simplify it) combination, where hopefully the resistance dominates the inductance and capacitance in your circuit. At microwave frequencies, it is painfully apparent that even the best resistors are highly imperfect.As for your definition of ground is concerned, that's only one type of ground. In practice your limited definition fails when sufficient current is flowing or the speed of light in the conductor is noticeable.

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2023, 10:32:03 pm
content: Quote from: tggzzz on March 14, 2023, 08:53:02 pmIf you think that’s a contradiction then you are functionally illiterate — or just trolling. The words “resistor” and “capacitor”, without the “ideal” qualifier, neither expressly mean a real-world part, nor an ideal one — it can be either, depending on context. That’s why we can add specifiers when needed.I’m not going to bother explaining to you what noun phrases, qualifiers, and adjectives are. But they are what make my statement be 100% true and yours to be pompous bullshit.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 10:37:51 pm
content: There was, in this thread, or other-where's, the question of whether "software engineering" is really engineering. That has to be looked at in terms of what software engineers do.If you tell me that you chicken farm produces 240 eggs a day and 2 "old hen" meat stocks a day, except Sundays.... that is what I will implement. I am not a chicken farmer. If you tell me the Vfe of a transistor is 4 times its VBE then that is what you will get.This, broad spanning across many domains is what causes frustration in many cases WITH software and software engineering in general.Usually in any one, or even an entire domain, a software engineer cannot answer the most basic questions about the data subject, it's cadence, controls, validations or otherwise. They just take data or process X or Y and translate it to process or store Y.Sounds like heaven to you? Try it. The transistor is a blank box. The customer is asking for valid and correct logging of it's characteristics. Profressionally I'm going to tell them I need an SME ... depending on the bottom line impact on insurance et. al. to "have a a crack or craic at it".Next week it's bus drivers and thier children and trying to use machine learning to work out holidays.On thursday it might be working out over the past 6 months what traffic light data recorded was valid and what was garbage submitted by the dodge hardware or the coms channel.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 10:42:02 pm
content: If someone wants to pay me to produce analysis of whether they got married on the right day or not... even if I understand a net 0, but am confused to a -19..... I can still full fill the engineering request.

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2023, 10:44:32 pm
content: Quote from: tggzzz on March 14, 2023, 09:13:39 pmEveryone except you understands that real-world parts have parasitics. But yes, you can buy a resistor: go look at any components vendor and you will find them. Literally thousands and thousands of different types. They’re called resistors and they give resistance. The fact that they also have parasitic capacitance and inductance is neither here nor there to the fact that theyareresistors.There’s this really neat concept I guess you’ve never heard of before, called “being more than one thing at a time, but having a primary one”.For example, I have three citizenships. If I say that I am American (which I consider to be my “primary” citizenship, i.e. my national identity), the fact that I also hold Swiss and Guatemalan citizenships don’t make me anylessAmerican, and formostpurposes, it simply doesn’t matter that I also have the other two. When I show up at the US border, they want to see my U.S. passport and that’s it — the existence of the other two is irrelevant. Are there edge cases where thecombinationmatters? Yes. But they’re very specific, like in taxes, military service, or extradition.

author: paulca
author_rank: Super Contributor
timestamp: March 14, 2023, 10:49:39 pm
content: GiGo.Oh wow. Thats like holy grail excuse. It never works.A HUGE portion of software engineering hours goes into to "otherwise" clauses, even the straw man ones.When this happens across an industry, they blame the SEs. The SEs couldn't really give a shit if out units are chickens, volts, children or goats. It's numbers.From a detail perspective within one singular domain customer, you are not in a position to argue as an EE. Shut up butter cup or write your own. SUBCORYO. I like it. :DD(Caveat* 1.4 bottles of red)

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2023, 11:31:46 pm
content: Quote from: tooki on March 14, 2023, 10:44:32 pm<Analogy snipped>You are confusing buying something called an X with something that is an X or an X+y.Shylock in "The Merchant of Venice" tried to claim his "pound of flesh" as repayment for a debt. During the hearing to excise the flesh, it is determined that he is entitled to his pound of flesh, but nothing else such as blood. Shylock is thus thwarted.Similarly, you will be thwarted if you attempt to get resistance without also getting inductance - but I doubt anyone would write a play about it.And that's an example attempting to argue by analogy! Fun aren't they.Any resistor or conductor that you buy will also have measurable inductance. As a rule of thumb, it will be around 1nH for every mm of length (wirewound resistors more or course!)Whether the amount of inductance matters depends on the circuit, of course. Given the OP mentions switching MOSFETs, the inductance may well be significant in this case.

author: jonpaul
author_rank: Super Contributor
timestamp: March 14, 2023, 11:47:58 pm
content: LT spice is,only one of many circuit Simulators. We used Altium and Intusoft ICAP4 for many projectshttp://www.intusoft.com/products.phpEvery component has parasitic and second order characteristics, but for most use these can be ignored.A schematic with symbols represents the ideal circuit without the parasitic stray L or C.Beware of simulatitis....getting stuck and wasted time trying to fix a poorly constructed or misbehaving Simulator.We could often prototype a circuit, tweak a,few,compoents, or swap ICS and easily measure V,I, in much,shorter time than to Simulate.We measured power with our fingers ( be careful!) or a thermocouple, IR temp meter.Bon SoiréeJon

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2023, 12:05:39 am
content: Agreed.It takes experience and judgement to use the necessary and sufficient models, and to assess whether the simulator or models are misbehaving.It can be enlightening to understand what's in IBIS models of ICs, and why. Hint: lots of LCR for each pin, plus more.I believe one advantage of MicroCap simulator over LTSpice is that it can read and use IBIS models.https://www.analog.com/en/analog-dialogue/articles/ibis-modeling-part-2-why-and-how-to-create-your-own-ibis-model.htmlOr

author: tooki
author_rank: Super Contributor
timestamp: March 15, 2023, 12:45:19 am
content: Quote from: tggzzz on March 14, 2023, 11:31:46 pmThat is not “confusion”, it’s showing you that those things exist in real life, under thenormaldefinition of them, not your imagined definition. You have gotten it in your head that the word “resistor” meansexclusively“ideal resistor”. But it doesn’t. If it did, the phrase “ideal resistor” wouldn’t exist.Quote from: tggzzz on March 14, 2023, 11:31:46 pmWell clearly you would, given how much you’re digging in your heels about your rigid, noncompliant private vocabulary.Quote from: tggzzz on March 14, 2023, 11:31:46 pmAnd nobody is claiming otherwise. Here’s the fact that you apparently refuse to accept:A real-world resistor (with parasitics) is a resistor.An ideal (=theoretical) resistor is a resistor.Ergo, your original claim that “resistors don’t exist” is complete and utter nonsense, just an arrogant mental exercise to try and show off to others, but in fact just demonstrating arrogance and rigid pedantry that disagrees with the standard vocabulary of the discipline, which just makes you look like you’re overcompensating, to be frank. It certainly isn’timprovinganyone’s perception of you…

author: james_s
author_rank: Super Contributor
timestamp: March 15, 2023, 12:52:53 am
content: Quote from: tggzzz on March 14, 2023, 09:13:39 pmThis is ridiculous, an absolutely absurd degree of pedantry that is not at all helpful to a beginner. I'm not sure if you are serious or just enjoy being deliberately obtuse for reasons that are beyond me.Textbook examples normally show ideal components, obviously the things you can buy are not ideal but they're still called resistors and capacitors, the same textbook will also cover the parasitic components. You don't have to specify that real world parts are not ideal because it is obvious, there's something called "context" which is very important.My definition of ground is perfectly adequate for the discussion at hand, which again is dependent on context.

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2023, 01:08:50 am
content: Quote from: james_s on March 15, 2023, 12:52:53 amThe only spec I can remember seeing for the OP's circuit involves PWM switching of high side MOSFETs. We know nothing about the construction technique. MOSFETs can be "damn fast", and have many interesting and surprising failure modes involving switching transients.Hence I don't think you have enough information available to assert that "My definition of ground is perfectly adequate for the discussion at hand". I'm willing to be corrected.

author: james_s
author_rank: Super Contributor
timestamp: March 15, 2023, 01:57:55 am
content: Quote from: tggzzz on March 15, 2023, 01:08:50 amGround is ground is ground, it's the reference point in the circuit. How ground is physically wired is a separate matter, it's still ground. Stop being obtuse, it's not helpful or constructive.

author: jonpaul
author_rank: Super Contributor
timestamp: March 15, 2023, 01:59:38 am
content: a " ground" connection 1 m long with 100 m ohms resistance to earth, may be fine for an audio amplifierThe same " ground" will be unusable for safety earth on a 10 hp motorFor a 2.4 or 5 ghz WiFi that same "ground" single wire inductance of some 50 NH will be a huge impedance problem.Thus the "ground" required changes,with current and frequencyJon

author: james_s
author_rank: Super Contributor
timestamp: March 15, 2023, 02:07:42 am
content: Quote from: jonpaul on March 15, 2023, 01:59:38 amOf course.But they're still called "ground". How it is physically implemented depends on the circuit, whole books could be written on the topic.

author: EPAIII
author_rank: Super Contributor
timestamp: March 15, 2023, 04:53:39 am
content: Beat me to it! Thanks.How the heck can we even begin to discuss this without even a photo of the OP's circuit?Quote from: golden_labels on March 14, 2023, 09:48:00 am

author: EPAIII
author_rank: Super Contributor
timestamp: March 15, 2023, 05:04:17 am
content: Quote from: EPAIII on March 15, 2023, 04:53:39 am

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2023, 08:44:43 am
content: Quote from: james_s on March 15, 2023, 02:07:42 amUnfortunately JonPaul omitted the context for his reply. Here is the important point, with my added emphasis...Quote from: james_s on March 15, 2023, 01:57:55 amI.e. a singular reference point, not one of several. In the examples JonPaul gave there can be no meaningful single reference point.The RF example may be more subtle, but the 10HP motor is pretty obvious: if you put one voltmeter terminal somewhere on the "ground" conductor and probe elsewhere on that conductor, then the displayed voltagewillbe non-zero and vary depending on the position of the probe.Your concept of groundrequiresall those measured voltages are zero. Reality trumps your flawed concept; sorry about that.

author: paulca
author_rank: Super Contributor
timestamp: March 16, 2023, 10:18:14 pm
content: OP software engineer. "Ideal real number". Riddled throughout tutorials. Should try harder and have a Big Decimal or just go do whatever the max precision your platform supports and .. minimise the problems or address them up front?This becomes a far more non-trivial aspect when two systems end up disagreeing by a single 3rd order decimal. Rounding and bit depth et. al. Floating point approximations. The "Maths" as written often doesn't work.The two parallels, electrical engineering and digital engineering are neither without their problems of approximations, measure or beware, ignore at your peril.I was recently reminded the reason why digital signal processors "normalise" to -1.0-1.0 range, is because that is where the highest precision exists for a give bit depth of floating point numbers. Like Donal... Close or far away. Big or small. Cows. It matters.Real world, floats are truncated agressively at agreed points far lower than the possibly min/max/eplison to minimise, but not negate errors. More ensuring that if such a rounding error occurs it is likely to occur on all sides.Siphoning rounding errors for profit has case law making it illegal, unless you are an investment bank, then it's fine.

author: paulca
author_rank: Super Contributor
timestamp: March 16, 2023, 10:33:04 pm
content: In contrast. Software scales differently. It is far, far easier for us to give the job of deciding and encapsulating that decision to a knowledgeable person and then forth with make all the "Dont need to know or care" developes use that "function". Or just import ... and understand... a "wide format" type like big decimal. It is NOT a 100% like for like for decimal. If it needs care and attention, we encapsulate that complexity and take it out of the hands of the inexperienced.Electronics scales, but not in the same way software scale. Electronics scales in "generations" where it takes a paradigm shift for formats on a global scale to change, such as the change from analogue telephony to digital and the same for radio and TV.Software can change, in todays world in milliseconds. Several recent outages in Google and Facebook have revealed just how fast a poison pill, deliberate, accidently or otherwise can destroy large portions of the live platform.In modern enterprise software design, a little like some electronics, is to out source and use off the shelf components for the "complicated parts". Exactly like EE uses ICs.If TI tested it and 1000 other peers tested it any I can test it, we should be good.Same into software and scale up rapidly to where "ICs" take days or hours to reproduce and instant to replicate.... Part of it is knowing where, as a human, to get out of the process entirely.As a backend developer (typically) I see my job most at risk of automation from AI. "Data Stoker" is a key candidate to become diesel engine. Not least I hate the role.Which... is obviously where I shall steer.Understanding the influx of data and processing it performantly and making of use to business... that will become the key skill. While informational therists may drive that, they will need the right "plumbing" and setup (for another few years).Maybe UI devs are just as fucked. Likely more. I found UI dev 50% fiddle with oddities and 50% breaking rocks in boiler plate.... or dealing with autogen code.

author: paulca
author_rank: Super Contributor
timestamp: March 16, 2023, 10:44:28 pm
content: There is nothing more satisfying as a software engineer to code something as simple as you guys would consider a transistor and years later look back and realise that EVERYTHING in the application relies upon it and the time spent by it is nonnegligible to the application total processing.Until someone suggests changing it.