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Voltage or current operated devices?

Discussion in 'General Electronics Chat' started by beakie, Jan 31, 2011.

  1. Ratchit

    Ratchit Well-Known Member

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    schmitt trigger,fernando_g

    So why should the OP be scared? And what if the number of posts are 100+? No one is forcing anyone to read this thread.

    Ratch
     
  2. schmitt trigger

    schmitt trigger Active Member

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    Ratchit;
    It was only an innocuous and tongue-in-cheek comment, an attempt to lighten up a heavy thread, but apparently you have to become upset at everyone.
    102
     
  3. Ratchit

    Ratchit Well-Known Member

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    schmitt trigger,

    What gave you that idea? I have seen comments before on long threads that were called things like "The thread from Hell", or insinuations that the OP's psyche would somehow be damaged. I am just curious about why folks get those ideas.

    Equally curious is why you have not remarked on a thread called "Help with Water Pump", which has been running for over two years, and whose length is 170 pages . A link is provided below.

    http://www.electro-tech-online.com/threads/help-with-water-pump.124250/

    Ratch
     
  4. dave

    Dave New Member

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  5. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Well then let me know when you *do* see it so we can discuss this further. If you can never see the other persons view then you can never discuss anything rationally.

    What i did was offer a reasonable way for you to come to grips with what i had been declaring, but you find a way to disagree with that too. So i think you should change your sig line to "Hopelessly Disagreeable" :)
     
  6. steveB

    steveB Well-Known Member Most Helpful Member

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    This is an incorrect statement. Feel free to respond if you feel I'm misunderstanding what you are trying to say here, but here is my logic.

    A 1 pF capacitor charged to 3.16 V has 3.16 pC of charge and 5 pJ of energy.

    A 1000 F supercapacitor charged to 3.16 V has 3160 C of charge and 5 kJ of energy.

    These are two devices I can order on-line, receive them in one day and charge up in my lab. Once I do that, they differ in both energy and charge by 15 orders of magnitude !

    So voltage does not imply the availablity of either energy or charge. And, voltage can be defined without any problem. It represents the potential energy that a hypothetical test charge (a small charge that does not disturb the fields) will have in the existing electric field. More formally, it is the line integral of electric field for a test charge as it moves between two points in an electric field. So, we are able to define and even measure voltage with a test charge with the most minimal amount of charge. There is the practical matter of just how small it can be, but in principle it can be very very small.

    Now we can ask the question, which capacitor might be more useful to bias and control a transistor? Obviously one capacitor does not have the energy or charge to affect the device at all, and the other might very well blow it up in a puff of smoke, if we are not careful.
     
  7. Ratchit

    Ratchit Well-Known Member

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    steveb,

    OK, let's look it over.

    Yes, your calculations are correct.

    Tilt! Since voltage is the electrical energy per unit charge (joules/coulomb = contentration), there has to be both energy and charge for voltage to exist. The two caps vary greatly in the amount of charge and energy they contain, but they both have the same concentration of energy per unit charge (voltage).

    Certainly for those two caps. They both have a finite amount of energy and charge.

    It represents the difference in potential energy a test charge has between two points within an electric field.

    Correct, and a definite integral is a difference between the values of a function between two points.

    The smallest a test charge can be is 1.6E-19 coulombs. So you are measuring voltage by moving a unit charge through a scalar energy field. Good, let's see where this goes.

    The scenario you describe does not mean that the small cap does not have both energy and charge. The fact that it does not have enough of either to do the job does not mean that has neither. Anytime you put a voltage across a cap, you are dealing with a finite amount of energy and charge.

    So to iterate and summarize. You cannot have voltage without energy and charge. That is basic to specifying a concentration of energy per unit charge. The fact that the electrical energy source cannot sustain the voltage does not abrogate that fact.

    Ratch
     
  8. Ratchit

    Ratchit Well-Known Member

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    MrAl,

    Or maybe "Hopelessly Hidebound".

    Ratch
     
  9. steveB

    steveB Well-Known Member Most Helpful Member

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    So, what you are saying is that a voltage implies that there is available "some finite amount of charge and energy", not that voltage alone implies the availability "of a suitable energy and charge" to do a particular job.

    OK, that makes more sense.

    To me this lends support to MrAl's viewpoint because if voltage really controlled anything alone, then any lone amount of finite charge and energy (no matter how small) would control and operate the device as long as it generated a voltage. But the capacitor example shows that voltage alone is not enough.

    In any event, since you place a high value on pedantics, I felt obligated to allow you to clarify your statement, because it struck me as an inaccurate statement without further explanation.
     
  10. Ratchit

    Ratchit Well-Known Member

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    steveB,

    Voltage is inextricably bound to energy and charge. A finite amount of energy and charge that defines a particular voltage may not be satisfactory if the voltage is not high enough or is not sustained. The example you gave confirms that.

    You said my example was inacccurate before, but I do not see how your example disproved what I said about voltage controlling a device. I averred before that even though charge was involved in voltage control, it was not controlling the device. The energy concentration was. That is proved in the diode equation by Schlockley and the physics of the diode.

    Ratch
     
  11. steveB

    steveB Well-Known Member Most Helpful Member

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    No, please let me be clear.

    I did not say your example was inaccurate. I was saying that your statement that I quoted was "incorrect". After i read your explanation and understood your viewpoint, i said that your statement was "inaccurate" without the additional explanation. With the explanation, it's fine. I say this because I interpreted your statement one way, and you explained it another way. And, the particular word that creates the ambiguity is "availability". Usually, available means "able to be used or obtained". If you had said "Voltage alone implies the existence of energy and charge", or "Voltage alone implies the presence of energy and charge", I would not have been confused by the meaning. But, "Voltage alone implies the availability of energy and charge" can be interpreted to mean that the voltage can supply the energy and charge, as needed.

    To make an analogy, imagine that the local "pedantic grocer" advertised that his store has "Peas available for purchase". Then, when a long line of customers gets there, they all find that he has only 2 peas sitting on the counter. Each customer walks out angry without purchasing the peas because 2 peas are useless to make a meal, yet the grocer claims that he is accurate in saying he has peas available for purchase to each customer, as they come in and complain about his inaccurate advertisement.

    Your examples and viewpoints? - I don't disagree with them for the most part. I accept them as a useful and workable point of view, and use that viewpoint often myself. I do, however, disagree with your opinion that your perspective is the absolute correct and only true way to view it because I don't generally view this type of question or discussion as one that can be formally proved. Even if it could be proved, there would need to be a much clearer statement of the question and clearer definitions of key words in the debate. Otherwise, the semantics are like slippery oils that allow Houdini to slide out of any attempt to pin him down.
     
  12. Ratchit

    Ratchit Well-Known Member

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    steveB,

    I agree with what you are saying. I should have made clear that voltage control also requires that the voltage will be sustained at a satisfactory level.

    Ratch
     
  13. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again Steve and Ratchet,

    Ratchet:
    "I should have made clear that voltage control also requires that the voltage will be sustained at a satisfactory level"

    You just voided your original statement whether you realize it or not. When you get down to basic physics you have to account for every little thing. Originally you said it was the voltage that did it, but now you add a conditional to that voltage, "sustained". So you've changed it from a single requirement:
    1. Voltage

    to the new requirement that now requires two things:
    1. Voltage
    2. Sustained

    Now ask yourself what that voltage needs in order to be 'sustained'. Answer: current. So another way to state this is simply:

    1. Voltage
    2. Current

    or more simply:
    1. Energy


    But Steve's nice example of the two capacitors should have put a lid on this already. I dont think it could be any clearer than that because we start with two finite amounts of energy both with the same terminal voltage, yet only one "operates" or "controls" the transistor while the other one can not. So that's a clear example how the voltage doesnt matter it's the energy available that matters. The voltage does not represent nor imply the "total" energy thus it doesnt make sense to say that voltage controls anything.

    The reason this paints a better picture is because the capacitors help to spell out the dynamics of the device to be controlled, while voltage alone can only describe the statics. We cant only care about the statics, we have to look well into the dynamics of the device in order to know how to control it. I tried to introduce the dynamics into the discussion when i brought up the time line. Looking at the device over time as the signals are applied helps to identify all of the concepts involved not just some.

    So to recap, to get a sustained voltage we need current and another way of saying this is simply that we need energy, but also knowing the voltage isnt good enough.

    We can say that a water faucet is 'force' controlled, but the static friction will sometimes prevent us from turning the handle because we didnt have enough energy to turn it. Given the min amount of energy required, we can then turn it. So without enough energy we cant turn (control) it, but with enough energy we can turn (control) it. That's the way everything in nature works. This isnt the best example perhaps.

    Steve:
    I'm happy to see that you joined the discussion. Hope to hear more from your end about this..
     
    Last edited: Feb 20, 2013
  14. Ratchit

    Ratchit Well-Known Member

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    MrAl,

    Actually, to sustain a voltage continuouly requires power if current is used. But so what? My original statement was about voltage control. What is requried to supply the voltage is irrelevant. I thought it was self-evident that whatever was required to sustain a voltage was necessary to exist, but not a factor in controlling a device. So I did not "void" my original premise that a device can be controlled by voltage even though charge and energy are necessary also.

    You are getting confused with how a voltage is supplied versus whether the voltage itself controls the transistor. The two cap example does nothing to clarify the voltage control of a transistor.

    The capacitors paint no picture at all with respect to voltage control of a transistor They only point out how a voltage may be supplied.

    So to iterate. The way a controlling voltage is obtained has nothing to do with whether a device is voltage controlled or not.

    Ratch
     
    Last edited: Feb 21, 2013
  15. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello again,



    Ok well then it's nice to hear that you found a 100 percent efficient diode or transistor somewhere. You should patent that thing right away.

    I on the other hand am using real world devices that are not 100 percent efficient. When something requires energy that is power so it's clear to see you're just playing with words now...good luck with that.

    Since you're just going to disagree with this too, i'll wait to see if Steve has anything else to add before i reply again if i do at all. The art of the debate is not simply a constant disagreement with anything and everything that is said that is contrary to your own opinion. That just leads to very uninteresting conversation.
     
  16. Ratchit

    Ratchit Well-Known Member

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    MrAl,

    Efficiency is not a factor as to whether a device is voltage or current controlled. That means that its usage of energy at a particular rate is is irrelevant with respect to control.

    I hope I explained my disagreement even though you do not agree with my reasoning.

    Ratch
     
  17. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Check this attachment.
     

    Attached Files:

    Last edited: Feb 22, 2013
    • Like Like x 1
  18. Ratchit

    Ratchit Well-Known Member

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    MrAl,

    Yes, amplifiers can be voltage amplifiers, current amplifiers, transconductance amplifiers, transimpedance amplifers, power amplifiers, etc. How does that tie into a semiconductor being a voltage controlled device?

    Ratch
     
  19. misterT

    misterT Well-Known Member Most Helpful Member

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    I thought you knew everything, but now you are confused..
     
  20. Ratchit

    Ratchit Well-Known Member

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    misterT,

    A lot perhaps, but not everything. Whatever gave you that belief?

    Not confused, but without knowledge of how MrAl's link relates to voltage control of semiconductors. There is a difference between lack of knowledge and confusion. Perhaps, since you appear to know what the link means, you could elucidate.

    Ratch
     
  21. Roff

    Roff Well-Known Member

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    I think misterT's comment was sarcasm...
     

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