Flux Capacitor Circuit Diagram

Discussion in 'Architecture & Engineering' started by Layman, Nov 25, 2014.

  1. leopold Valued Senior Member

    i've done a reasonable amount of circuit analysis, both AC and DC and i've never used the term dq/dt for current.
    can you explain to me what i'm missing?

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  3. Trippy ALEA IACTA EST Staff Member

    q is charge. Current is the rate of flow of charge with respect to time. Amps = Coulombs/second. Volts = Joules/Coulomb.
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  5. leopold Valued Senior Member

    ok, this explains what it is.
    how is this term used in circuit analysis?
    i'm not being nit picky here, i'm curious as to why i was able to determine DC bias points and AC solutions without using it.

    second question, the explanation you give seems to suggest dq/dt is related to the time constant of the circuit in question.
    are they related?
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  7. Trippy ALEA IACTA EST Staff Member

    In part because it determines how capacitors and inductors behave and is affected by resistance.
    When dq/dt = 0 capacitors act as open circuits and inductors behave as resistors.

    If, for example, we consider a RC circuit, then the time constant is R*C
    R is measured in ohms, which is J.s/C²
    C is measured in farads, which is C²/J
    And so when we multiply the two together we're left with a number measured in seconds which is related to the number of packets of charge flowing around a circuit and the energy associated with each packet - in this case it turns out to be the amount of time required to charge the capacitor to some specific level.
  8. leopold Valued Senior Member

    i believe most circuits can be solved for DC by a combination of ohms law, kirchoffs law, and a smattering of transistor parameters.
    AC solutions require capacitive and inductive reactance.
    there are exceptions though, the reflected secondary resistance of transformers for example.

    anyway, is the curve for dq/dt the same as the RC time constant curve?
    if it is, then that's the reason i never used dq/dt
  9. krash661 [MK6] transitioning scifi to reality Valued Senior Member

    i have been trying to follow it. from what i have been able to read, here and there, i find this topic interesting.
  10. Aqueous Id flat Earth skeptic Valued Senior Member

    What Trippy said:, add the total number of Coulombs passing through a node for one second, and that tells you how many Amperes are flowing. I brought this up because Layman believes a capacitor can charge (thereby elevating the voltage across the terminals) without current flowing.

    My main point is that we can measure the available energy at the output of his circuit by E=qV, where q is the Coulombs of available charge sitting at V volts. That can never be greater than or equal to the energy used to produce the charge at that voltage in the first place, due to conservation of energy. Notice that Power = dE/dt = d/dt(qV) = (dq/dt)(V) = Vi. It may seem a little pointless, but it's always good to walk through relations like this to double-check units, and to reinforce basic concepts. Both are lacking in Layman's approach to design.

    For some reason Layman went into a Creationist argument, or something of that sort, trying to say that, if the universe came from nothing, then conservation of energy was violated, therefore he can violate it at will, and produce free energy, simply by arbitrarily picking components and wiring them together as he sees fit. That puts him in a very cranky position to be engaging folks here on questions of electrical engineering.

    As a side remark, since the main issue here is energy, I would strongly suggest that everyone who ever actually wanted to understand the limitations on technology, insofar as energy is concerned, begin by creating a chart that illustrates all the forms of energy you can think of. For example, here I have explained that E = qV but of course I could write that several other ways, e.g., E = P × t = Vi × t. Continue this as a list of categories and you'll keep thinking of more forms until you eventually run out of ideas:

    Categories of energy:

    Static electricity: E = qV
    Electric current: E = Vi × t
    Planetary gravity: E = mgh
    Linear kinetic: E = 1/2 mv²
    Torque: E = τθ
    Pneumatic: E = PV (ideal gas law)
    Thermal: E = nRT (ideal gas law)
    Wind: E = 1/2 Atρv3
    Electrochemical: E = qV (from table of half cell reactions, using mass of electrode erosion × valence to get q)

    and so on. Then you can quite simply estimate the max available energy from any machine or device that converts energy from one form to another. Of course if you take every permutations of these, you end up with some odd kind of machines, such as one that uses a falling weight to pressurize a gas, or one that uses static electricity to produce wind. And so on. But a few of these, the ones that apply to steam turbines and generators, are of great interest, as well as the limits on batteries and renewable sources. Of course these are only upper limits based on idealizations. In practice, the designs become very complicated as you attempt to make them more and more efficient.
  11. leopold Valued Senior Member

    and my point is, you can solve a 5 or 6 stage transistor amplifier for DC without ever using the above formulas.
    the AC solution is even simpler because it takes into account only the capacitance and inductance, and gives you the passband of the amp.

    the formulas you are using seem to be connected with the AC solution because it has a varying quantity.
    capacitive reactanc (XC) and inductive reactance (XL) are used instead.
    like i said, this yields an AC solution.

    i have no idea why layman would go off on a creationist tangent.
    maybe he's hoping god will swoop down here and fix his circuit.
  12. leopold Valued Senior Member

    it's my guess that curve for dq/dt is identical to the time constant of the circuit in question.
    i don't know about anyone else but i've always used the formulas for capacitve and inductive reactance for AC solutions.

    kirkoffs laws are used when dealing with multiple power sources.
  13. Aqueous Id flat Earth skeptic Valued Senior Member

    Yeah I brought it up to as a teaching point for Layman, to learn how to apply conser?v
  14. leopold Valued Senior Member

    i don't know trippy all that well, but it's a safe bet he isn't a stoner.
    where are you layman, get a hold of an unplugged capacitor?
  15. caliskan Registered Member

    Layman, I think people in this thread seriously need to read up on electronics. There are people randomly shifting topic from how capacitor can supply power to a circuit to cryogenic materials operating at sub-zero temperatures. It is very important to some people to understand that in order to actually understand and diagnose their issues, they need to respect the people who provide them with solutions.
  16. origin In a democracy you deserve the leaders you elect. Valued Senior Member

    Agreed, but Layman refuses to listen.

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