LTSpice variable Resistor with voltage and current

Discussion in 'General Electronics Chat' started by ulix, May 21, 2015.

  1. ulix

    Thread Starter New Member

    May 21, 2015
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    Hello,

    I want to simulate a variable resistor, for which I have the current and voltage date (0V, 0.5V, 1V, 2V, 4V, 6V, 8V, 10V) How can I get this realized? Everything I tested didn't get me in the simulation on the x-axes the voltage and on the y-axes the current...
    cheers
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Is the resistor non-linear ( a function of the voltage across it), or do you just want to vary the resistor to see what effect that has on the operation of the circuit?
     
  3. ulix

    Thread Starter New Member

    May 21, 2015
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    it's non linear, from a light-bulb. I only have the voltage and current data.
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You can make a non-linear resistor by setting its value to some variable, like this:
    Non-linearResistor.gif
     
  5. ulix

    Thread Starter New Member

    May 21, 2015
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    Sorry, I don't understand. How can I import the voltage current data? it's all dc voltage
     
  6. Alec_t

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    Sep 17, 2013
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    I suggest you plot your data and from the graph deduce an equation which gives resistance as a function of current or voltage. Then use that equation to set the sim resistor value.
     
  7. ulix

    Thread Starter New Member

    May 21, 2015
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    How can I get the function? Is there no other way? In PSpice it works with the GTABLE Command, you put TABLE = (u_1, i_1) (u_2, i_2) ....
     
    Last edited: May 21, 2015
  8. ulix

    Thread Starter New Member

    May 21, 2015
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    Ok, I calculated a function, can LtSpice handle ^2 functions?
     
  9. Alec_t

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    You write it as **2.
     
    ulix likes this.
  10. ulix

    Thread Starter New Member

    May 21, 2015
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    Well, my function is: f(x)=-5.7942*10^-4 * x^2 + 0.01416x + 7.3299*10^-3. But it doesn't replay the correct value. Can I display the voltage current as function in ltspice?
    The right value is: V(vr)=1.695V and 31.8mA
     
  11. ulix

    Thread Starter New Member

    May 21, 2015
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    Alec_t you are great, mate! I got it. I read your post again, I didn't make a function for R, at first I did it for I.
    cheers!
     
  12. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Sure, just plot the expression V(vr)/I(R5).

    Here is an example of how to make a resistor a function of a node voltage in LTSpice. I also show how to plot the resistance of R1.


    219.gif

    I am guessing that your function R=f(x) is not correct. I sure doesn't resemble any light bulb I have ever modeled.
     
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