Problem with LTspice: Time stop too small

[Firenze02]

Hi,

I'm trying to create a variable resistor dependign from the value of current.

Please find attached the .asc file.

It doesn't work, when I run the simulation the following messages is presented:

Analysis: Time step too small; initial timepoint: trouble with node "n002".

Do you know how to fix this problem?

Thank you.

 

[unclejed613]

i don't have ltspice on my machine here, so i'm going by what i see in the asc file. i don't see a ground symbol listed. you also can't have a recursive (recursive on itself? that's a math nightmare) value for the resistor. instead you would need to use a behavioral voltage or current source. i think it's the recursive nature of the resistor value that's causing the math to crash.

it's been my experience that ltspice needs a stable starting point. if you give ltspice a recursive value, or a circuit that's unstable (like an op amp with the inputs swapped backwards) ltspice will try to find an operating point to start with, but the recursive nature of the calculation will keep ltspice from pinning one down, and so it tries to shorten the time steps to see if it can find a stable condition. if it can't stabilize, it will spit out "time step too short" errors. if it somehow manages to stabilize, it will very slowly calculate voltages and currents, and may display oscillations or random noise. basically, ltspice is chasing it's tail.