1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Why this curve is going down? Why the current is negative?

Discussion in 'General Electronics Chat' started by sr13579, Jan 2, 2018.

  1. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    28
    Likes:
    0
    Please take a look at the graph and tell me what is wrong? Why it is going downward.
    I use this mobile app to simulate the circuit.
    Is there anyone who use this app?
     

    Attached Files:

  2. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,450
    Likes:
    991
    Location:
    Loveland, CO USA
    ONLINE
    The screen shots are too small for me to see.
    what app?
     
    • Disagree Disagree x 1
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,676
    Likes:
    959
    Location:
    Canada, of course!
    The circuit is simply a 9V battery with a 1k ohms load resistor.
    The sweep might be the voltage in the battery dropping and the "curve" is the resulting reduction in the current of the circuit.
     
    • Like Like x 1
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

    Joined:
    Mar 28, 2011
    Messages:
    9,376
    Likes:
    920
    Location:
    Rochdale UK
    ONLINE

    WeSpice... Apparently only $9 for Android..
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,676
    Likes:
    959
    Location:
    Canada, of course!
    The problems with the images are:
    1) Too small, they should be double the size posted.
    2) Negative faint grey lines and letters on a black background instead of a normal positive image of black lines and letters on a white background.
    3) Saved as a very fuzzy JPG file type instead of as a very clear PNG file type.
     
    • Agree Agree x 1
  7. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,450
    Likes:
    991
    Location:
    Loveland, CO USA
    ONLINE
    I agree with the AudioGuru. A sweep function takes one (or more) values and shows what happens if that value varies. In this case it looks like the battery is "swept" from 0 to 9 volts. I think this is not the function you want. Sorry I don't know this program.

    Many of us use LT Spice. (free and good)
     
  8. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    28
    Likes:
    0
    Can you help now?
     

    Attached Files:

  9. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,369
    Likes:
    1,234
    Location:
    Cardiff, Wales
    The graph slopes down because the current into V1 is negative and its magnitude increases as V1 voltage increases. Spice shows current direction as into a component.
     
  10. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,450
    Likes:
    991
    Location:
    Loveland, CO USA
    ONLINE
    You have a window "DC transfer characteristic". I think you want a different option there.
    Now you are plotting "V" against I. Where V changes from 0 to 9.

    I think you want "DC ?????". I don't know the exact words. DC something. There should be a place for entering time. "0 to 100mS"
     
  11. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    28
    Likes:
    0
    How am I supposed to fix this?
     
  12. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,369
    Likes:
    1,234
    Location:
    Cardiff, Wales
    It isn't a fault that needs 'fixing'. It's a Spice feature.
     
  13. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    28
    Likes:
    0
    But PSPICE does it correct on PC?
    What is wrong here?
    I have done this on PC.
     
  14. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,450
    Likes:
    991
    Location:
    Loveland, CO USA
    ONLINE
    I understand you can read this picture but I can't. Where did you answer the question about what program is this?
    If you want help don't give out bad ratings.
    upload_2018-1-2_12-31-46.jpeg
    On LT Spice, and others, you can change "I(V1)" to "-I(V1).
    OR
    On other spices, you can change "I(V1) to I(R1). OR -I(R1) This way you are plotting the current in the resistor. OR negative current.
    If I(R1) plots negative you can try removing the resistor and rotating 180 and putting it back.
     
  15. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    28
    Likes:
    0
    Is there any way to run this by code?(This is NGSpice engine.)
     
  16. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,450
    Likes:
    991
    Location:
    Loveland, CO USA
    ONLINE
  17. alec_t

    alec_t Well-Known Member Most Helpful Member

    Joined:
    Jul 10, 2011
    Messages:
    9,369
    Likes:
    1,234
    Location:
    Cardiff, Wales
    Nothing. LTspice does the same as your Spice.
     
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,676
    Likes:
    959
    Location:
    Canada, of course!
    The red line has two kinks but it should be straight. It is correct at 3mA and 3V across the 1k resistor up to 7mA and 7V across the 1k resistor. Below 3 and above 7 the red line is wrong.
     
  19. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,210
    Likes:
    569
    Location:
    AZ 86334
    It is a static circuit. You can only do an .OP "operating point" analysis on it...

    71.png

    If you want to see what happens if you change V1, then use a .DC sweep. It plots the independent variable V(V1) on the x-axis, and the dependent variable(s) I(R1) on the y-axis.

    71a.png

    The current through R1 [I(R1)] is positive by convention. If you apply KCL to the circuit, which way does the current through the source V1 have to flow? By convention, when a source is delivering current to a load, it is a negative current. That is the way engineers (and Spice) work...
     
    Last edited: Jan 2, 2018

Share This Page