Talk:RLC circuit/Archive 1

Archive 1

Archive 2

Fundamental versus derived parameters

There seems to be some confusion about which parameters are fundamental, and which ones are derived. The article is a bit inconsistent. Right now, the article identifies the natural frequency and the Q factor as fundamental, while it says the bandwidth BW and damping factor alpha are derived. But the equations for the Q factor and the bandwidth define these parameters in terms of the damping factor alpha. So if the Q factor is fundamental, why is it defined in terms of another parameter that is supposedly derived?

Meanwhile, the damping factor is defined in terms of R and L, which are the values of the circuit elements, and not in terms of any of the other parameters. So why is alpha called a derived parameter when in fact it does not depend on any of the other parameters?

Bottom line: the fundamental parameters should be the natural frequency and the damping factor. The derived parameters should be the Q factor and the bandwidth.

Rdrosson 15:37, 13 October 2005 (UTC)

I have made this change. Notice that the two fundamental parameters are now defined in terms of the circuit elements only (R, L, and C) and not in terms of any other parameter. Notice also that you can derive any other parameter in terms of these two fundamental ones – including the Q factor, the bandwidth, the damped frequency (which is not shown), the pole locations, the zero locations, and even the second order differential equation that governs the circuit's behavior.

Notice also that the Q factor must come last, since it is defined in terms of the bandwidth BW.

Rdrosson 16:01, 13 October 2005 (UTC)

I have also added a (brief) definition of the damped resonance.Rdrosson 16:33, 13 October 2005 (UTC)

Image

This image is prettier in a way, but the other one is easier to make sense of. I think I will replace both with my own anyway. - Omegatron 02:39, Jul 16, 2004 (UTC)

Parallel RLC schematic

I suggest we use the textbook example where all components are in parallel and driven by a current source. We can show that this is the exact dual of the series case driven by a voltage source. Any thoughts? Madhu

Driven by a current source, you say? - Omegatron 20:57, Mar 26, 2005 (UTC)

I agree with Madhu. First of all, it makes no sense to connect a voltage source in parallel with a resistor. The resistor has absolutely no impact whatsoever on the circuit, you could actually remove the resistor without have any effect on the circuit's behavior. Second, a current source in parallel with a resistor (a Norton Equivalent) is the exact dual of a voltage source in series with a resistor (a Thevenin Equivalent). And third, Madhu is correct that the parallel RLC is the exact dual of the series RLC, but only if you replace the voltage source in the series circuit with a current source in the parallel circuit. Do the math, the two circuits result in the same exact differential equation, and the same results (if you swap all of your variables with their duals). – Rdrosson

I agree with Madhu and Rdrosson. I teached 30 years electric circuits in Belgium. People don't like current sources. In mechanics are force and speed sources. Nevertheless I admire the work of Omegatron.

File:Rlc2.jpg

Tsi43318 15:22, 11 February 2007 (UTC)

The bottom line is that a series resonant circuit, when driven by a voltage source consumes maximum power at resonance when Z = R. The power consumed reduces to a half of maximum (the definition of the cut off points) when the magnitude of the circuit impedance increases by a factor of 1.414 (square root of 2). A parallel resonant circuit on ther other hand, when driven by a current source, consumes maximum power at resonance when z = R. The power consumed reduces to half of the maximum when the magnitude of the circuit impedance falls by a factor of 1.414. If a series resonant circuit is driven with a current source the consumed power is constant. Similarly, if a simple* parallel resonant circuit is driven with a voltage source, the consumed power is constant. In short, for basic analysis, series resonant circuits should be driven with a voltage source and parallel resonant circuits should be driven by a current source.

• Simple does not necessarily relate to practical circuits, but relates to RLC all in parallel. Even practical parallel circuits (when suitable simplifications/approximations are made) are best described as driven by current sources. Monicandave (talk) 21:59, 7 January 2012 (UTC)

The Parallel RLC circuit diagram is not correct. It should either use a current source in parallel with the resistor (a Norton-equivalent power source), or it should use a voltage source with a series resistor (a Thevenin-equivalent power source). But it most definitely should not have a voltage source in parallel with a resistor. If you do not believe that, please consider the schematic diagram as it is now in comparison to the same circuit but with the resistor removed completely from the circuit. You will notice that the voltage across the inductor and capacitor are exactly the same in either case. So what purpose does the resistor serve? Absolutely none. First Harmonic (talk) 00:57, 19 July 2011 (UTC)

In my own opinion, I think everyone is missing the point here. We are talking about the schematic for a parallel RLC. For example, I think everyone would agree that the picture at the top of the wiki page is a good physical representation of a series RLC. We could even resolder those components to make a picture of a parallel RLC. Now, if I ask anyone to make schematics for these images, I think most would omit the driving source – there isn’t one. Thus this would mean the caption for figure 1 inaccurate. It is not a “RLC series circuit” but a “RLC series circuit being driven by a constant DC voltage source”. A similar problem exists in this discussion of the parallel RLC. Everyone is discussing how a parallel RLC circuit is to be used, not how a parallel RLC circuit is represented in a schematic – which is the topic here. As we can see, the voltage/current source clouds the issue and, if present, should really be in another part of this fine article. Jotdot (talk) 20:22, 14 January 2012 (UTC)

To Do

1. Transient analysis using Laplace transform
2. Step function
3. Sine drive at resonance (this is interesting!) Madhu

Progress to date

1. I have started a discussion of the Laplace Transform as a method for solving the ZSR. – Rdrosson
2. ...
3. ...

Needs some work

There are some small things that needs to be fixed up:

• If the resonant frequency is in hertz then need to say what units are used for L an C (says lower down but should say before used).
• Alpha is used to categorize Overdamped/underdamped/critically damped but alpha is never defined (and I can't remember what the term for alpha is, the root something of the differential equation in math and the dampng something or other in electroincs, I think, it's been a while).

Note: I have done substantial work over the last day or so to define alpha. In the standard approach to RLC circuits, alpha (in radians per second) is called the damping factor or damping parameter. It is one of two important parameters, the other of which is the natural frequency (also in radians per second) or ω_o. – Rdrosson

The hard things is that it looks too hard (though this is a matter of opinion and I don't know what to do about it). This looks to be written at the level of a 3rd year college engineering student (who has had circuits, calculus and differential equations). I'd like to try to simplify it enough to be interesting to a freshman. Like I said, I don't know if this is possible. (I need to see if I still have my text book) I sympathise about the 'looking too' hard comment. I really find it difficult to explain to my students what is happening and isolate it from the maths and differential equations. This is something which could be applied to alot of wiki pages and I think a format change generally would help. With, where possible a laymans/childs/worded/pictorial section followed by more rigorous theory. It is easy to say that this isn't possible, but I believe it is nearly always possible to give a factually accurate but much simplified explanation for something as long as perhaps a few underlying links are studied first. Monicandave (talk) 22:48, 7 January 2012 (UTC)

new images

Use as you please:

Anything else I should label? - Omegatron 20:55, Mar 26, 2005 (UTC)

The diagrams are fine, except I think you should change the parallel RLC by replacing the voltage source V with a current source I. The symbol for a current source is a circle (just like the voltage source) with an arrow pointing along the diameter of the circle instead of the little "+" and "–" signs. It looks like a schematic for a compass. In this case, the arrow would align with the vertical and point in the upward direction. Rdrosson

Are you going for negative values for current, if not your current is going the wrong way. PiP (talk) 22:32, 6 December 2007 (UTC)

bandpass filter image

I would like this better if it were log-o-rhythmic. Or if such was added side by side. I want to try my hand at making pretty gnuplot diagrams a lá Image:dba_plot.png, but someone else is free to beat me to it. - Omegatron 23:32, Mar 28, 2005 (UTC)

Simplify Zero Input Response?

As RJFJR noted, this article is written at a fairly high level- I imagine most students are going to encounter RLCs before they do any differential equations- so I'm working on reworking this part of the article to use the cheating workaround that I've seen in classes, where you just sort of say "I(t) = Ae^kt, because it should, now let's solve for k- now we've got α" That way all we're assuming is high school algebra, simple trig, and De Moivre's Thereom.

I'm also considering adding a part that would describe a steady-state solution with a driving voltage. My biggest worry is that this article will end up being very incongruous, but I think it's preferable so long as the first part is as transparent as possible. --Hal 20:49, 1 August 2005 (UTC)

Centering equations

why are all the equations centered? Wikipedia:How_to_write_a_Wikipedia_article_on_Mathematics#Typesetting_of_mathematical_formulas

Note: I have eliminated most of the centering of equations. Equations are now left justified with an indentation of two tabs. – Rdrosson

The schematic with definitions beside it looks kind of nice, but the gray background conflicts with the schematic background. I have the original xcf files I think, and could make it transparent, but... - Omegatron 16:05, August 5, 2005 (UTC)

Also variables should really only be bold if they are vectors... - Omegatron 14:59, August 7, 2005 (UTC)

translation request at top

what is that, a joke? Pfalstad 19:29, 25 September 2005 (UTC)

oh, I see.. Wikipedia_talk:MediaWiki_namespace_text#Math_equations_to_plain_english I don't think there's much point in that, in this article anyway. (At first I thought it was a sarcastic complaint about the complexity of the formulas.) Pfalstad 23:12, 28 September 2005 (UTC)

The formula are not simple to read. It'd be nice to have a plain english translation of the equations. JDR (seem to have some support to translate formulas ... as seen here)

Damping factor

I had not realised before that damping factor has dimensions of angular frequency (rad/s)!. So I have learned something new after all these years thanks to WP. Hooray!--Light current 23:56, 13 October 2005 (UTC). I wonder if this has any deeper signigficance.- must ponder it!--Light current 00:26, 14 October 2005 (UTC)

Uh oh. There are two electrical definitions of damping factor. We need a disambig, it would seem. — Omegatron 00:13, 14 October 2005 (UTC)

Yes the one you're referring to is the audio one of Zl/Zs. for the electro mechanical damping of a speaker cone but are they different things or the same thing in another guise. I dont know!--Light current 00:23, 14 October 2005 (UTC)

To Omegatron:

where do you see two definitions of "damping factor"? I have seen an entry for damping, which provides a pretty good description of the general concept, using the well-known mass-and-spring harmonic oscillator as an example. Where are you seeing two electrical definitions? Do the two definitions conflict with one another, or are they redundant, or what? --Rdrosson 02:50, 15 October 2005 (UTC)

Nevermind....I see the problem now. The article called Damping factor is talking about a concept completely different from the use of damping factor in the RLC Circuit article. Unfortunately, it appears that the same term is used in each of these contexts to mean very different things. The term is actually a bit of a misnomer in the context of amplifiers and bridging circuits, where it might have been better to call it the "attenuation factor," which is closer to the meaning in that context. Nevertheless, I think you are right in saying that we need to add a disambiguation page. -- Rdrosson 03:02, 15 October 2005 (UTC)

On further inspection, the article entitled damping is not so great. It needs some heavy editing to clean up the notation and the flow of ideas. With a bit of work, it could be converted into a very good parallel to the RLC Circuit article, so that each article would help support the other from a different point of view. RLC is a perfect analogue for Damper-Mass-Spring.... -- Rdrosson 03:21, 15 October 2005 (UTC)

Recent edits

Moved from my talk so everyone can make comment. -- Light Current

Reply from Rdrosson

Thank you for the compliment on the editing I have done on RLC Circuit. I have worked very hard on this topic (and a few others) during the last three months, and I hope that my contributions have improved these entries.

With all due respect, I have to say that overall, I am not at all thrilled with the changes that you have made to RLC Circuit since this morning. In fact, I think the article is far more confusing than it was prior to your revisions. Let me make a few comments:

Resonance Frequency

• Terminology: there is really no such thing as a "resonance frequency." There are two correct terms, which are "resonant frequency" or "resonance." The issue is related to correct grammar: "resonance" is a noun, whereas "resonant" is an adjective. The word "frequency" is of course a noun, so you must precede "frequency" with an adjective, not with another noun.

Symbols and Notation

• Symbols: On the one hand, the choice of symbols or notation really shouldn't matter, since they are really rather arbitrary. On the other hand, making good choices about notation can help clarify a difficult topic immensely, whereas making poor choices can take the simplest idea and make it incomprehensible. That being said, the difference between good and bad notation in any particular case is obviously quite subjective and open to debate. Nevertheless, I have a lot of experience as both a student and a teacher, and I think I have pretty good judgement on this issue. Furthermore, there are large sets of notation that have become standard, at least within a functional discipline or sub-discipline such as mathematics, physics, or engineering. Unfortunately, there are often differing standards from one discipline to another, which creates some confusion. And in some cases, I believe that some of the standard notation is rather confusing and difficult to master.

In any event, I am really disappointed with the notation changes that you made to many of the equations earlier today. For example, I am really opposed to using the Greek letter zeta (ζ) as a symbol for anything, primarily because it is very seldom used and very few people have any idea what it is when they see it (including me). Furthermore, I have seen many many textbooks in electrical engineering and many many university professors who all use the Greek letter alpha (α) to represent the damping factor not only in RLC circuits, but also in all second-order linear systems.

I have never seen anyone use beta (β) to represent bandwidth (in rad/s), but I thought it was an excellent choice, and certainly better than delta-omega, since it is the next letter in the Greek alphabet after alpha, and since the letter beta is a good mnemonic for the word "bandwidth." And I didn't think anyone would be too concerned with using BW to represent bandwidth in units of hertz.

Passive versus Active Voice

• I can understand that you might want to change things from the active voice to the passive voice, since that is very common in scientific and technical writing. That, of course, does not actually improve the writing. In fact, I think it actually makes the writing substantially weaker.

Think about the difference in meaning between the words "active" and "passive." Would you rather work with people who are generally passive, sitting back and waiting for something to happen, or those who are active, who pick up the ball and run with it, who actually make things happen? It is not a perfect analogy to writing, but it's not a bad analogy either. I want writing that steps up and grabs hold of the reader, not writing that sits back and waits for the reader to figure it out.

The active voice is actually a far superior style of writing, even though it is not standard among scientists and engineers. I have never understood why anyone would choose to use the passive voice in any kind of writing, except in very rare circumstances.

I don't mean to be hyper-critical, but it is kind of frustrating to put so much effort and hard work into something only to see someone else dismantle it. Sorry.

I will probably have some more comments tomorrow, but right now I need to get some sleep.

See 'ya, Rdrosson 03:22, 14 October 2005 (UTC)

Reply from Light Current

Unfortunately, this is what often happens on WP. You put your heart and soul into an article only to have someone come along and, in your opinion, trash it!. This has happened to me on many occaisions and I used to get very angry about it. Over the past few weeks however, I have found that in some cases, the comments and changes made by others have actually been correct and I have been wrong and had to eat humble pie! But it is only after long and sometimes tense discussions that I have realised it. Remember, that no one can claim sole authorship of an article, and we all should try to help to make it the best that it possibly can be.

Now having said that, if I were you, I would take some comfort from the fact that I congratulated you on your good work. Thats more than I've ever had from anyone. I did think it was good. Very good in fact. But not perfect! Articles will never be perfect and can always be improved/corrected. Ive generally only had blanket reversions and quite a lot of (mild) abuse.

I do sympathise with you, but you really have to toughen up on WP, and try not to be too sensistive. Its not easy, but if you listen to other peoples points of view closely enough, you may even find yourself agreeng with them. Remember, in general, comments are not aimed at you personally but in improving the quality of the article. If you can bear that in mind, I think you may find things easier. The article is the important thing, not anyones ego! Generally, on the science and engineering pages, we do not get into edit wars etc. We have robust arguments on the talk pages, but we never (not usually anyway) get too personal. That way, we work together for the general good of WP>

I hope this makes you feel a bit better and would encourage you to continue to contribute. As I said you seem to have a logical mind: we could do with some of that. See you around I hope!--Light current 04:32, 14 October 2005 (UTC)

Resonance Frequency

How can a frequency be resonant? The terminology is wrong in the books and has been for years. You can have a resonant circuit or some other resonant system, but the adjective resonant cannot be used with the word frequency Im afraid! A frequency is a frequency - thats it! Could be a frequency of resonance if you prefer.

Is this more of your original research? If the books are all "wrong", then this article should contain the "wrong" terminology that's in all the books, because that's the consensus, and our job as an encylopedia is to report the consensus view, not your view. Google reports 757,000 hits for resonant frequency, 947 hits for "frequency of resonance". If you want to change the accepted terminology, go write a paper and submit it to an ee journal or something. Pfalstad 05:37, 14 October 2005 (UTC)

Now, now. No need to get uptight! I think there is at least one person who agrees with me on this one! Open your mind. You are an intelligent fellow Im sure, so you neednt believe all you read without question. By your reckoning since ten giga-giga flies eat crap- it must taste good!--Light current 05:45, 14 October 2005 (UTC)

"open your mind"? You're the one saying that all the textbooks are wrong and only you are right. It's not a question of belief, it's a question of terminology. Hey, I just noticed that the word "stopband" is wrong because a filter doesn't actually "stop" frequencies, just attenuates them. Should we remove that word from wikipedia too? Pfalstad 16:15, 14 October 2005 (UTC)

Gramatically, resonance frequency is without doubt correct, but anyone working in the field for any length of time will relate to and know that the term most frequently used is resonant frequency. To be honest I don't care which is used as long as the underlying meaning is clear. Would prefer articles in this class were accurate and understandable. Within reason, most are searching for knowledge, not an English lesson. Monicandave (talk) 22:11, 7 January 2012 (UTC)

res·o·nant (rĕz'ə-nənt) pronunciation

adj.

2. Producing or exhibiting resonance — Omegatron 06:55, 14 October 2005 (UTC)

No original research. Also, Wikipedia is not a publisher of original thought or a chat room. It's fine to have some discussions about article content but lots of speculation about the way things really are and all that should go to a discussion board. We report on the way things are; not the way we think things should be (for the most part). — Omegatron 07:05, 14 October 2005 (UTC)

And what way are they?--Light current 17:04, 14 October 2005 (UTC)

Right-or-wrong, the vast majority of the literature uses one of two terms: "resonant frequency" or just plain old "resonance." I have never seen the term "resonance frequency" in any textbook or journal article on the subject. Furthermore, I simply do not think that "resonance frequency" sounds right, and frankly, it looks like a typographical error. --Rdrosson 13:01, 14 October 2005 (UTC)

Well how about 'frequency of resonance'. It sounds OK and has 947 google hits. Its more accurate than resonant because it can be applied to 'frequency' whereas 'resonant' can't. Anyway I leave it to the majority view! I smell my other fish burning! ;-)--Light current 17:04, 14 October 2005 (UTC)

No. It's non-standard, and "resonant frequency", meaning "a frequency producing or exhibiting resonance" is perfectly accurate. — Omegatron 23:05, 14 October 2005 (UTC)

Just because something is non-standard doesn't mean it is incorrect. I had a physics professor make the assertion that resonance frequency was correct for exactly the same reasons (i.e. "resonant frequency" is incorrect as we're referring to the frequency of the resonance and the frequency is not itself resonant). See also a point of view from 1971, apparently: http://users.ece.gatech.edu/mleach/misc/resonance.html So, no, this is not an unheard-of discussion. — Mixed signal2 (talk) 22:31, 22 November 2011 (UTC)

By the way, there are countless examples of common usage in the same pattern: "interview suit," "party hat," "fishing rod," "mountain bike," etc. So the argument that resonance in "resonance frequency" is trying to be an adjective is beside the point; this occurs in English all the time. See, for example, http://en.wikipedia.org/wiki/Adjective#Other_noun_modifiers -- Mixed signal2 (talk) 22:51, 22 November 2011 (UTC)

OK. I said I leave it to the majority view--Light current 23:09, 14 October 2005 (UTC)

Example of non-parallel non-series RLC circuit

I think an example of a circuit with other configurations than parallel and series devices would be helpful - I know it would help me right now. I can't get these friggin DE's solved. I guess i'll just use laplace transforms.. - but if anyone could produce another example, it would be helpful to see how a more complicated RLC circuit could work out. Fresheneesz 08:40, 21 April 2006 (UTC)

embellisment of damping factor

Is there a general definition of damping factor (the type defined here)? I've been looking for a way I can derive the damping factor, but I can't seem to find anything. Can anyone help? Fresheneesz 00:34, 5 June 2006 (UTC)

Step Response?

I think what this page needs is a Step response section. I havn't got the time now, but if someone can, please add that section! —The preceding unsigned comment was added by Yjxiao (talk • contribs) 05:01, 17 April 2007 (UTC).

Damping Factor Confusion

I see in this article the editor has confused the normalized tamping factor with the unnormalized one.

If you loo at section "Derived Parameters" you can see the damping factor is defined

$2\zeta ={R \over L}$

for a series circuit , while in the section "Fundamental Parameters / Damping Factor" it is defined as:

$\zeta ={R{\sqrt {C}} \over 2{\sqrt {L}}}$

That's because he mistook the damping factor in the first case for the normalized damping factor in the second.

So I decided to add an "N" subindex to the normalized one, and state that in the description.

There are actually two different but equivalent ways that most textbooks approach this issue. The first approach defines a parameter called the attenuation α (in radians per second) as

$2\alpha ={R \over L}$

or equivalently

$\alpha ={R \over 2L}$

The second approach defines the damping factor as the attenuation normalized by the resonant frequency:

$\zeta ={\alpha \over \omega _{0}}={R{\sqrt {C}} \over 2{\sqrt {L}}}$

The two approaches are obviously complementary, and either is perfectly valid.

I have edited the article to reflect the standard notation used by most textbooks.

First Harmonic (talk) 08:18, 16 August 2008 (UTC)

Bandwidth

I'm 90% sure that the bandwidth stuff is wrong. The ratio R/XL is not the bandwidth in Hz but the Q factor (Hz) of the circuit. Similarly R/L is the Q factor (rads-1) of the circuit. The Bandwidth in return is the natural frequency over the Q factor. This is all explained in Q-factor. (nevermind, I was wrong)

Not sure who did all of the section, but it def needs a rewrite, with the parallel RLC included as well.

125.238.84.108 (talk) 23:09, 10 November 2008 (UTC)

resonant capacitor

Is a resonant capacitor some special component I am unfamiliar with? Or is it merely an ordinary capacitor in a RLC circuit (or a LC circuit)? --68.0.124.33 (talk) 15:15, 8 January 2009 (UTC)

Now marked as a hoax. SpinningSpark 09:37, 10 January 2009 (UTC)

Spring analogy

I feel that this article should have a link to or incorporate it's exact correspondence with the mathematical model of a damped spring. -Craig Pemberton (talk) 18:58, 13 October 2009 (UTC)

pulled link discussion

I have put in my former link and opened this discussion

http://www.fourier-series.com/RLC-Circuit/index.html

Under the RLC circuit article you removed a link I provided and said that personal websites are not allowed. Did you look at the content of the RLC tutorials? It has detailed information on the transient response the steady state response and the impulse response. My website is no more personal than several of the other links on this page.

Thanks —Preceding unsigned comment added by 76.181.44.43 (talk) 03:04, 2 December 2009 (UTC)

First of all, if one of your edits is reverted, the correct response is to open a discussion (as you have done), not to immmediately re-instate the edit, please see WP:BRD and avoid edit warring. The quality of other external links is beside the point, each one should be judged on its own merits, see other stuff exists. We are discussing the one that you inserted. It would literally be a lifetimes work to check the suitability of every link on Wikipedia and there are bound to be many unsuitable ones. These can be dealt with as they are highlighted, but right now let's stick to the one that popped up in people's watchlists because a change was made to the article.

Wikipedia is about writing articles here, not linking to other people's web sites. There is no factual material, that could not be, or is not already, incorporated in the article. Have you read the external link guideline?, particularly that one should avoid any site that does not provide a unique resource beyond what the article would contain if it became a Featured article.

And yes, I have read your website, including the statement I barely learned enough to pass the exams.

SpinningSpark 11:31, 2 December 2009 (UTC)

I will not reinstate the link. I wished to initiate a discussion about whether the material covered in the three programs merited a link on this wiki page. Rather than disussing the content of the three programs you have placed what can only be considered an insult as your response. The quote is completely out of context. —Preceding unsigned comment added by 70.62.154.132 (talk) 14:05, 2 December 2009 (UTC)

Q Factor

This page seems to give one equation for the Q factor for RLC circuits, but Q factor gives one for series and the reciprocal for parallel RLC circuits. Aaron Schulz 04:08, 27 January 2010 (UTC)

Natural frequency and resonant frequency

This edit is confusing the natural damped resonant frequency of the circuit with the driven resonant frequency. The first is indeed obtained by solving the differential equation for the circuit. However, the resonant frequency the article is discussing is the frequency at which the impedance becomes purely real and is found by forming the equation for the circuit impedance. This is not the same frequency as the natural frequency.

The bottom line is that the material is referenced to a reliable source, whereas the amendment is unsourced. It is not acceptable to write new material under a reference which no longer agrees with it. SpinningSpark 17:23, 13 August 2010 (UTC)

Kirchhoff

According to Prof. Walter Lewin of MIT, Kirchhoff's loop rule doesn't hold in RLC circuits, because there is a changing magnetic field in the self-inductor. The curl of the electric field is not zero in that case (Faraday's law) and Kirchhoff requires a zero. http://www.youtube.com/mit#p/c/C2CEECFD938FD494/25/QwUgYBzdcrM http://ocw.mit.edu/courses/physics/8-02-electricity-and-magnetism-spring-2002/lecture-notes/lecsup41.pdf

He also says most textbooks get it wrong there. Just thought I'd throw that in here. Mapar007 20:00, 15 March 2011 (UTC) — Preceding unsigned comment added by Mapar007 (talk • contribs)

Kirchhoff's_circuit_laws#Limitations —Preceding unsigned comment added by 96.224.70.38 (talk) 14:29, 26 April 2011 (UTC)

I would say a discussion of that doesn't belong in this article. Kirchhoff's laws give the correct voltage appearing at the terminals of the inductor and that is all that is of interest in a gross circuit. SpinningSpark 18:57, 26 April 2011 (UTC)

Critical damping

As of 2011-05-03: "The special case of ζ = 1 is called critical damping and represents the case of a circuit that is just on the border of oscillation. It is the minimum damping that can be applied without causing oscillation." I don't think of damping as "causing" anything, so I would reword the second sentence to say "It is the maximum damping that can be applied and still have oscillation" or "It is the least damping that can be applied while still allowing oscillation." But I don't want to change it unless someone else who knows a little more than me agrees. —Preceding unsigned comment added by 74.111.107.137 (talk) 01:53, 4 May 2011 (UTC)

I have moved your post under a new sub-head as it is really a new thread. Take as an example a series RLC circuit with a square wave as input and an adjustable capacitor. Damping causes oscillation in the sense that as the capacitance is decreased through critical damping oscillation will start. Nevertheless, I am not against a rewording, but both of your suggestions are erroneous. There is no oscillation at critical damping and your second suggestion also has the direction wrong. SpinningSpark 06:12, 4 May 2011 (UTC)

Significance of equation

If Q is big then α is small. The RLC circuit will oscillate and ω_d=ω_o. If Q is small then α is big and the circuit does not oscillate because it's overdamped. What is the mathematical significance of the result of the ω_d equation in the "Transient response" section? I assume the magnitude of α will be bigger than ω_o so the square root will be over a negative number which is going to produce an imaginary number. Would that mean that no real components are present so this is why there is no oscillation?

ICE77 (talk) 22:43, 12 May 2011 (UTC)

Strange equations for the Series case

Is the form of Kirchoff's equations shown in the Series section common in the EE community or somewhere else? It looks odd to me from a physicists perspective.

The first equation is normal. The second one is a bit odd, but still passable. I can imagine that his currents are easier to measure, it is nice to get the equation in terms of currents. To my eye it is clearer to replace the integral of i(t) with q, but it is understandable.

The truly strange part comes next. The text says " For the case where the source is an unchanging voltage, differentiating and dividing by L leads to the second order differential equation:"

Why would you want to make the assumption of "unchanging voltage", when the non-homogenous version of the same differential equation can be obtained just by shifting from i(t) to q(t). In other words, why not deal with:

${{d^{2}q(t)} \over {dt^{2}}}+{R \over L}{{dq(t)} \over {dt}}+{1 \over {LC}}q(t)=v(t)$

instead of

${{d^{2}i(t)} \over {dt^{2}}}+{R \over L}{{di(t)} \over {dt}}+{1 \over {LC}}i(t)=0$

Sure, in that case you have to take the derivative of q to get back to i(t) for your final solution, but you are then solving a more general differential equation.

Crumley (talk) 17:33, 31 May 2011 (UTC)

Revealing the truth about electrical resonance phenomenon

I have copied the text below from Electrical resonance talk page. Please, discuss. Circuit dreamer (talk, contribs, email) 22:29, 21 July 2011 (UTC)

Bless my soul! I know it looks strange and incredibly, and probably you will not believe me... but I have finally revealed the secret of the ubiquitous electrical resonance phenomenon! It is interesting that the negative impedance phenomenon has helped me to find out credible intuitive explanations about the impedances of series and parallel LC circuits. I would like first to share my insights with you here; then to compress these lengthy explanations into a few sentences and to place them in the main article...

Realizing the LC arrangement

The fault of the classic formal approach when explaining the zero and infinite impedance of series and parallel AC-supplied LC circuits is that it implies two dual impedances (inductive and capacitive) that cancel each other thus giving total zero or infinite LC impedance. But this widespread assertion is misleading...

It is hard for people to imagine how two humble impedances can cancel each other as "impedance" gives an impression of something passive. Two passive "things" shouldn't cancel each other; one of them should be active (a source). So, we have to consider an LC circuit as a combination of two elements: a source (active element) driving a load (passive element). Depending on the situation, the either element (the inductor or capacitor) can act as a source; meantime, the other element will act as a load. Strictly speaking, both they are sources containing energy (magnetic or electric); but figuratively speaking, the load is a source that is "forced" to act as a load (like a charging accumulator). They can be distinguished by the signs of the current through and the voltage across them - in the source they are different while in the load they are equal.

Why the impedance of a series LC circuit is zero

We have an arrangement consisting of four elements connected in series: an AC input voltage source, an inductor, a capacitor and a load (a resistor). Or, we may combine the input voltage source and the resistor into a real voltage source (with internal resistance).

The main article says: "Inductive reactance magnitudeX_L increases as frequency increases while capacitive reactance magnitude X_C decreases with the increase in frequency. At a particular frequency these two reactances are equal in magnitude but opposite in sign; so X_L and X_C cancel each other out. The only opposition to a current is coil resistance. Hence in series resonance the current is maximum at resonant frequency". Let's now try to comprehend this magic...

According to the considerations about LC arrangement above, we can think of the series LC circuit as of an AC source and impedance connected in series. At the resonant frequency, this "source" has the same polarity as the input source; the two AC voltages are in phase with each other so they add together. Let's for concreteness consider the voltage polarities travelling along the loop at both the half waves.

Positive input half wave (travelling clockwise): -V_IN+ (source), +V_LOAD- (impedance), -V_L+ (source), +V_C- (impedance). The charged inductor acts as a source that "helps" the input source. Note the voltage across the inductor (the source) is equal to the voltage drop across the capacitor (the impedance) so the total voltage across the series LC circuit is zero. Its total impedance is zero and it does not impede the current. Very interesting... as though the inductor acts as a negative capacitor or as the output part of the op-amp in an inverting integrator that neutralize the capacitor impedance! Well, there is still a subtle difference:) The true negative capacitor and the op-amp use additional external energy (a power supply) for this purpose while this "negative capacitor" draws energy from the input source.

Negative input half wave (travelling counterclockwise): -V_IN+ (source), -V_C+ (source), +V_L- (impedance), +V_LOAD- (impedance). Now the charged capacitor acts as a source "helping" the input source. The voltage across the capacitor (the source) is equal to the voltage drop across the inductor (the impedance) so the total voltage across the series LC circuit is zero again; its total impedance is zero and it does not impede the current again. Now as though the capacitor acts as a negative inductor that neutralizes the inductor impedance!

We can generalize the two cases by one conclusion: An AC supplied series LC circuit consists of two elements connected in series and having equal voltages across them; one of the elements acts as a voltage source while the other acts as impedance.

It is interesting fact that from this negative impedance viewpoint, both the reactive elements can have negative impedance in this sense. They change alternatively their roles: once the inductor acts as a negative impedance element, then the capacitor does the same and so on, and so forth...

You might mention that this type of circuit has been used to simulate the electrical properties of electrical power transmission line sections in electrical power distribution studies.WFPM (talk) 19:06, 21 February 2012 (UTC) In this case the bottom line is considered to be the ground leg and the extension legs are connected across the capacitor.WFPM (talk) 19:12, 21 February 2012 (UTC)

Why the impedance of a parallel LC circuit is infinite

Now we have a simpler arrangement consisting of two elements: an AC input voltage source driving an LC tank.

The main article says: "Let R be the internal resistance of the coil. When X_L equals X_C, the reactive branch currents are equal and opposite. Hence they cancel out each other to give minimum current in the main line. Since total current is minimum, in this state the total impedance is maximum."

To comprehend this assertion as above, we can now think of the parallel LC circuit as of an AC "helping" source and impedance connected in parallel. At the resonant frequency, the "source" provides all the current needed for charging the impedance to the input voltage; so there is no need the input source to do this donkey work:) The helping "source" as though acts as a load canceller (i.e., as a negative impedance again)! Actually, this arrangement is similar to the exotic bootstrapping technique: a voltage "source" (i.e., the LC tank) is connected in opposite direction to the input voltage source; as a result, the current is almost zero and the impedance is infinite. Of course, there is a subtle difference again:)

Circuit dreamer (talk, contribs, email) 22:12, 21 July 2011 (UTC)

LC shunt in a 50 ohm BNC line

I wanted to ask whether putting an LC shunt on a 50 ohm terminated BNC cable is equivalent to this circuit...Anyone know? --HappyCamper 18:40, 4 February 2012 (UTC)

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