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Discussion in 'Electronic Basics' started by Wong, Sep 6, 2004.

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  1. Wong

    Wong Guest

    Based on this circuit, I have some strange results from simulations.

    / 2K
    |--------------------------o C
    | |
    | |
    \ |
    / 2K |
    \ |
    | |
    | |
    | |
    o o
    A B
  2. John Larkin

    John Larkin Guest

    Aren't B and C the same node?

  3. Wong

    Wong Guest

    But with point A equal to 0v. The node between 2 resistors should have
    2.5v according to the voltage divider rule. So this is something that
    I am not so sure with the 'mix' of 2.5v and 5v (point B).
    Is point C still 5v under this circumstances ?
  4. John Miller

    John Miller Guest

    If the ASCII drawing is correct, B and C will always be the same; they are
    directly connected.

    John Miller
    Email address: domain,; username, jsm

    A diplomat is a man who can convince his wife she'd look stout in a fur
  5. Do you have a connection to ground in your circuit? Electronics Workbench
    (Multisim) and similar simulators need one, in order to calculate voltages.
  6. Randy Day

    Randy Day Guest

    This is correct, as long as *no voltage* is being
    applied at point B. The resistance between B and C
    is 0 ohms, so Vc will always equal Vb.
    The voltage chart is correct for the circuit as drawn.

    If you connect B to 5v, you're putting a 0 (that's zero)
    ohm resistance in parallel with the upper 2k resistor.
    What does your 'voltage divider rule' say about this?

    If you connect B to A (0v), you're putting a 0 (that's zero)
    ohm resistance in parallel with the *lower* 2k resistor.
    What does your 'voltage divider rule' say about this?
  7. John Larkin

    John Larkin Guest

    It would if nothing else is connected to it. But when you apply a hard
    voltage source to the junction, the source wins.

    Please don't top post.

  8. Jamie

    Jamie Guest

    Point B and C are connected! why shouldn't they be the same?
    just think about that.
    if Point B is applied voltage from a source its ovbious that
    Point C will look the same.
  9. Wong

    Wong Guest

    Think that I am confused by the word 'input' and 'output'. FYI, A & B
    label as input points and C point is output. And I have been given the
    waveforms of C in the middle of 0v to 5v(half Vcc) for A=0v and B=5v.
    Yup, u guys are correct since output C is followed input of point B.
  10. Mortel

    Mortel Guest

    When you say "0v" do you mean putting the point to ground or letting it
    floating. There's a big difference between the two options.

    If point A is floating (not connected to anything...) you have 0v connected
    to this point BUT there is no current flowing on the branch... so you can
    remove the entire line from point A to the next node (with the 2k resistor)
    since this part of the circuit is doing nothing.

    If A is connected to Ground (zero volt), current can flow between point A
    and the rest of the circuit. You can then apply voltage dividing and
    current dividing rules.

    Also, when you say " [...] pint A equal 0v [...]" is it a measured voltage
    or an applied voltage ? You have to do the distinction between these
    notions for us (and you) to understand what you are doing.

    I think that you are on a good way to succeed your simulation, you're
    probably not doing exactly what you want to do. Be shure that, in all time,
    all your points are connected (either to ground, source or instruments).

    If point B = 5v then point C = 5v (same node), the upper resistor is
    shortcutted (no voltage difference on it). You can then ignore this branch.

    If point A = 5v and point B = 5v then point C = 5v and no current is flowing
    on the circuit.
    If point A = gnd and point B = 5v then C = 5V and a current is inducted in
    the 2K resistor (I let you do the math... I = V/R).

    For clarity, be shure to define the conditions on all nodes an any time.


    Jean-François Martel

  11. Wong

    Wong Guest

    Mind to explain what is measured voltage and applied voltage? What's
    the different ?
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