Timeline for Does a current source practically exist
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| Nov 8, 2016 at 14:48 | comment | added | LvW | Did you read again my answer - in particular the EDIT part? I have some experience in teaching students and engineers - and I have learned that it is not a bad idea to encourage even newcomers to be critical and curious. Do you really think, an answer like the foillowing would be of great help to the OP? : "Yes - a practical current source does exist - see the following example." Such an information - together with many circuit examples - could be better found in wikipedia etc. I think, a forum like this one should allow better and more detailed answers. | |
| Nov 8, 2016 at 12:01 | comment | added | Russell McMahon♦ | ... Most people seem unaware of how tenuous the reality of our reality is, how "imaginary friends" and/or utter impossibility are the only rational 'explanations' of reality, and that most (if not all) attempts at reasoned logical approaches demand that we make semi-arbitrary assumptions - which we are largely unaware of doing. All good fun. | |
| Nov 8, 2016 at 11:58 | comment | added | Russell McMahon♦ | I am NOT meaning to 'make fun of you' - I'm sorry o\if it seemed that way. BUT, I AM having fun. It is not too often that one gets to discuss reality, existence or philosophy in general on SE EE. Such opportunities should be cherished, embellished and relished. Probably :-). I think about (believe it or no) existence, reality, perceptions , perspectives, use of words, "normality" and similar most of the time, while simultaneously trying to think of too much else as well. I think that in this case we have all strayed towards excessive philosophy compared o what the OP intended, BUT ... | |
| Nov 8, 2016 at 11:35 | comment | added | LvW | RusselMcMahon, thank you for the story. But I ask myself: Why are you making fun about me and my word "philosophical resp. linguistic aspects"? Do you not understand? Perhaps you find a moment to think more deeply about the term "source" - and how we are using this term (and others) in our daily life. Is a solar panel really a source of energy? And - regarding this thread - is an electronic device we call "current source" really a "source" of current? Or isnt it rather a source of another quantity that "allows" a current? Shouldn`t we - from time to time - reflect our own use of words? | |
| Nov 8, 2016 at 10:37 | comment | added | Russell McMahon♦ | From memory ... :-) - "There once was a man who said, God, Must find it exceedingly odd, When he sees that the tree, continues to be, when there's no-one about in the Quad". ||| & the response: "Dear sir, your astonishment's odd, I am always about in the Quad, And that's why the tree, continues to be, As observed by, yours faithfully, God. " :-) | |
| Nov 8, 2016 at 8:00 | comment | added | LvW | RussellMcMahon, I have no problems in case "none of the other answers" agree with my "claim" (really a claim?). | |
| Nov 8, 2016 at 7:11 | comment | added | Russell McMahon♦ | None of the other answers agree with your claim re "philosophical point". Most touch in passing on the concept of an ideal xxx versus a practical xxx. BUT if you agree (as I think you will) that there exists a practical voltage source, resistor, capacitor, LED, transistor, inductor ... THEN there equally exists a practical current source. Yes? If not then nothing "practical" "exists" (which according to QM and Bishop Berkeley may well be the case, and all is well in the garden. | |
| Nov 7, 2016 at 10:38 | comment | added | LvW | Yes - I have expected the example of a solar panel. But also in this case, one could discuss if there is a charge imbalance which is the cause of a current. Nevertheless - the whole question touches - more or less - "philosophical" or "linguistic" aspects because of the word "exist". I think, you will agree to this, don`t you? | |
| Nov 7, 2016 at 10:32 | comment | added | Russell McMahon♦ | ... panels (and cells) are current sources first and voltage sources second. Their voltage is close to constant across their Iout range and Iout is nicely proporional to solar (or other) insolation. At a given insolation level and constant load they are close to ideal insolation controlled current sources and far less close to being controlled voltage sources.The figure of merit (fill factor) and cell efficicny both improve as the cell becomes closer to ideal. So the answer to your question is "yes, in a non ideal manner", I think. | |
| Nov 7, 2016 at 10:28 | comment | added | Russell McMahon♦ | " ... which does get its energy NOT from a voltage source? ... " is a question to which no answer could, for you, exist, as voltage and current when energy is being transferred are unavoidably entangled. Reverse V & I in the question and it is no more or less possible. || A Weston standard cell is a not to bad example of a current source and a voltage source simultaneously. Nothing should be done to dequibrillate the cell in terms of either voltage or current if it is do achieve its appointed task. We see it as a voltage reference but it is equally a current reference. || Modern PV ... | |
| Nov 7, 2016 at 9:51 | history | edited | LvW | CC BY-SA 3.0 |
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| Nov 7, 2016 at 9:22 | comment | added | LvW | RusselMcMahon - he was also asking "..or is it just a concept ?". And I think, yes - it is just a "concept". We call a source "current source", when it is able to deliver a "nearly" constant current. However, in reality it is always a regulated/controlled voltage source (from th physical point of view). Finally, let me ask you: Do you know a "practical current source" which does get its energy NOT from a voltage source? Movement of charges needs a corresponding force (provided by the E-field, resp. the related voltage). | |
| Nov 7, 2016 at 8:54 | comment | added | Russell McMahon♦ | Not really - he was not asking about ideal sources, but "do practical ones exist". And they do. A current source need no more be made from a voltage source than vice versa. It's our normal view of things that makes it seem so. If all supplies were shorted when not in use and designed accordingly the isual supply would be a current source. | |
| Nov 7, 2016 at 8:08 | history | answered | LvW | CC BY-SA 3.0 |