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Registered Member #1517
Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304
Hey guys,
I have a problem. I have very little motivation to learn complex circuit analysis techniques for my Circuits 2 class. Mostly because my professor is a terrible teacher, and also because I am having trouble seeing the point.
How important/ how often do you use stuff like the Laplace transform, s-domain analysis, bode plots, poles and zeroes, and all the other junk? Do you use it for designing your circuits for your projects? What should I pay attention to and why?
Part of the reason that my professor is bad is that he gives us absolutely no big picture scheme of why we should be learning these tools. Granted that we should just accept they are important and try to learn them, I am a big picture sort of guy. I learn much more if I have a place to put things, such as a bode plot. If I can say to myself, "oh yeah, I could totally use that," or "I can see why that works." I find much more meaning in class.
Right now it just feels like a bunch of junk, taught by a junky professor. I am not a slacker, I really do try in his class, but he just fails where it matters I guess. As proof of his ineptitude, I visited him in his office hours at the start of class, to introduce myself and tell him about my Tesla coil I was building. I figured that he'd be interested and maybe know a few things about the project. I have never seen such a display of apathy in any educator to date... not one hint of surprise, interest, or even a trace glimer of joy that at least one of his students wanted to actually learn something from his class. In another meeting, I was trying to get a good mental model for node voltage analysis. I was good at doing every other type of analysis except node voltage and decided it was high time to fix that. He yelled at me that I should quit his class and that I was wasting his time, during his scheduled office hours... at 9am....
Its ok because I later found out that he's a complete dope, so no hard feelings.
Anyways, bottom line is... where am I gonna see this stuff again? Should I really try and learn it? I am genuinely interested in electronics, but feel a bit lost on where to dig in...
PS. Some background on me, physics/mechatronic (robotics) engineer
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
All of that so-called "junk" suddenly becomes priceless the day you have to start designing circuits that use negative feedback. Whether it's making a low-distortion audio amp, or getting a Segway to stand upright, or programming the DSP in a heat-seeking missile, you usually think of the dynamics of the loop in terms of Laplace transforms, Bode plots and the Nyquist criterion.
(The easiest way to estimate the Nyquist stability margins is graphically with a Bode plot, and the easiest way to get to the Bode plot is to calculate your system's transfer function in the s-domain and decompose it into the standard Laplace transforms for differentiators, integrators, lead-lag networks, second-order resonances, and so on.)
If you're not familiar with all of the above, then you have no mental model for how feedback loops work, and you can't make progress except by tacking capacitors onto things at random until it stops oscillating.
(OK, I lied about the missile, digital control loops are analyzed with z-transforms instead of Laplace.)
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
How important/ how often do you use stuff like the Laplace transform, s-domain analysis, bode plots, poles and zeroes, and all the other junk? Do you use it for designing your circuits for your projects? What should I pay attention to and why?
Well, Steve is Mr. Ph'd.
I've worked in power electronics for almost 15 years, developing many different types of power supplies using all sorts of different topologies with both voltage and current mode control. I've never used a Laplace transform. In fact, in my entire power group (i work for one of the world's largest defense contractors), i've only seen one person actually use a Laplace transformer.
Bode plots on the otherhand are very important, so you should know how to develop and interpret them. However, will all the tools available today, there is no reason you need to go in manually and calculate a loop using Laplace or any other type of transforms.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
All courses are packed with stuff that will rarely be used in the real world afterwards, so the material sinks down into the sludge at the bottom of your mind, where it waits half-forgotten until the day comes when you find you need a piece of it to solve a particular problem.
Being competent always involves having more knowledge at your disposal than 99% of problems actually need to solve them.
In any case, how can you know now what you may need to know in future - unless we are talking about a McJob here? Large fries or regular, sir?
Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
Whether you see it again or not is not the point, in my mind. Perhaps the best questions to ask myself would be:
Do I want to understand how the Laplace transform works, just in case I need it in the future?
Might it help me when faced with those horrible systems of linear differential equations in next year's DE class?
Oh no! I need to develop a loop filter for a PLL for minimum noise!! How do I do that!
There are Laplace transforms....and Fourier, Z, Mellin, Hilbert, wavelet transforms (and who knows how many others). How are they related and what are they good for?
Is an education something that I receive passively, expecting to be spoon fed from a (possibly boring) professor, or is it something that I demand to have and will actively take it wherever and however I can?
Do I want to be the best engineer/scientist that I can, seeking to understand new concepts and applying them in new and wonderful ways?
Feel free to add to this list...
In your case, self study or study with other interested students is likely to yield good results. Lots of hours with books in the library...... Playing with Matlab or Octave could possibly be useful. Kirchhof's Laws are a good place to start....as you have indicated in your post... The Laplace transform in circuit theory is just a useful way to turn systems of differential equations in time into algebraic equations (in the so-called s or complex frequency domain) that are more compact and easier to solve than the DEs... Basically, there are lots of simulators that can do this for you, but it is nice to understand how these simulators work..
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
Laplace transforms are pretty handy. The other day I needed to solve a differential equation, and my DE solving skills are very weak from lack of use. But a quick Laplace transform, some algebra, then inverse Laplace transform, and I had the answer. Of course, for this example you could just as easily say that I should remember how to solve DE's instead of Laplace transforms. But when you're analyzing complicated circuits in the frequency domain, Laplace transforms can be priceless if there are more than a couple inductors/capacitors. In case your prof is just throwing theory at you without application, analyzing a circuit in frequency domain means that you are determining its response to sine waves, as a function of the frequency of the waves. And with Laplace transforms, this means you can find both the transient and steady-state response of a circuit to various inputs.
In undergrad you can get away with not understanding basic concepts like Laplace transforms and Bode plots very well. In grad school, I am now wishing that I tried a lot harder in my basic engineering and math classes, because it turns out that almost everything you learn is important, depending on your emphasis. It will rarely hurt you to understand too much theory, but it can definitely hurt you if you know too little.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Unless you have a post-graduation plan it's impossible to advise which topics are worth the effort, (I've not done a Laplace transform since Uni. but many bode plots- hobby and professionally possibly because I understand and have a 'feel' for 'gain and phase', but Laplace is just math to me, More effort into the mastery of Laplacian Transforms MAY have altered my career path)
Education is a great privilege and a fantastic opportunity!
You should make full use of your opportunity, academically and socially, by the time you graduate things may be a little tough, so you will do better if you have good qualifications and friends.
Now for the hard part, you have to decide what to go for (reclusive Mad Scientist - Academic - Research - Development - Technician etc. ) (all of the above may be considered 'charity work' because vast wealth is unlikely) or some other path?
Once you've got an idea of your general direction you can concentrate on key areas (never forgetting the immediate goal of an excellent academic qualification) You have to be self-motivated, who else can truly motivate you? Grab the opportunity, actively persue knowledge, friends, culture, fun....... Sitting on the grass watching the girls go by (etc. etc.) was great, but it didn't help long-term.
P.S. It appears that for all practical purposes, the capacity of the human brain is limitless, so you don't have to worry that you may learn too much ;)
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
Perfect example:
Without knowing Laplace how do you obtain the equavilent circuit? How do you intereperet the phase changes on the first plot, how do you design a realized circuit based on your observed results... you can't. The fact is you will encounter some problem which will require guesstimates and some intuition, and you will have to go out on a limb with only your data to support you, and you will have to take a stab at a hard problem that no one wants to deal with, and be right!
Filter design, Control systems (my major), RF engineering, everyting really, employs simulation, anaylsis, and of course optimization. These are important tools for you to have in your toolbox, so do your best to learn them now because:
1. There is no time to learn them during the exam, and I promise you its on the exam
2. There is no time to learn them on the job, and I promise you it will happen on the job at some point.
3. If you don't know it, they may find someone who does, and then what do you do for a job?
Believe me, I have had my hurdles with the same material, It sucks!, but it's more important to struggle with it now then later.
coil 5
Coil 5 unterminated.
Coil 5 ground terminated.
I'm going to evaluate both modes to try to satisfy my curiosity about the open/short filter characteristics of the coil. I know what one of the equivalent circuits looks like from the ARRL handbook, but the graphs will hopefully help me determine the exact values of the parasitics which will lead to a more accurate model of the coil as a system and not just a simplified model.
Registered Member #1517
Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304
Thanks everyone.
This is exactly what I needed. To put a name like PLL, filters or just simplifying circuits to predict responses is what I had a trace feeling all this stuff was about but it was never confirmed by either the professor or my own limited investigation.
Would you say that its nearly impossible to understand a bode plot or the like, if a professor decided to skip over Laplace transforms because another professor is supposed to be teaching them in a future semester?
I am glad I came here and asked this, I just borrowed a book on solid state theory from my physics collection, and was really getting into it. But I felt guilty that I wasn't even fully up to speed on the subject material in Circuits 2. Now that I know what I am looking for I will have an equal thirst for learning the middle of this circuits book.
It is comforting to hear that others interested in electronics have struggled with learning some of the concepts, like the Laplace, and other circuit analysis techniques. Perhaps it was the way it was presented to me, for some reason I could not see its application or use... strange. We'll see how difficult it is now that I have a place to put it in my mind.
I do have a final tomorrow morning at 8am in circuits 2. I expect some very simple stuff... node/mesh/ impedance/ power transfer/ transient and complete response/ no laplace/ maybe a bode plot/ poles and zeroes...
My tesla coil exhibits some irregular behavior.. I was thinking about generating the circuit in spice and taking a look at what it may be doing... perhaps a phase is out of whack. I was reading about PFC's and thought it might be whats up with my coil. But that's another topic for another thread...
Registered Member #1792
Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527
coillah wrote ...
Would you say that its nearly impossible to understand a bode plot or the like, if a professor decided to skip over Laplace transforms because another professor is supposed to be teaching them in a future semester?
It is comforting to hear that others interested in electronics have struggled with learning some of the concepts, like the Laplace, and other circuit analysis techniques. Perhaps it was the way it was presented to me, for some reason I could not see its application or use... strange. We'll see how difficult it is now that I have a place to put it in my mind.
You don't need to know anything about Laplace transforms in order to understand bode plots. The Laplace transform is one way to derive the bode plot of a filter, amplifier, or some system, but ultimately the bode plot is just a response of a system to various inputs. If you had a physical system and the right equipment you could measure the bode plot without a bit of mathematical theory. You can also get a bode plot by solving the system of differential equations you get by mesh/nodal analysis of a circuit.
Engineering is (in my opinion) a challenging major. I have always had a hard time fully understanding the very "mathy" fileds in EE, such as control systems and signal processing, which is probably why I gravitated towards RF circuits.
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Motivation for learning
