LM2907 – Too many iterations without convergence – Proteus


I am trying to use LM2907 to convert a frecuency signal into a voltage signal. The frequency signal comes from a motor encoder and it´s supposed to be connected to pin 1 from the LM2907, but I am getting an error that is coming from this connection, as it disappears when I leave the pin opened. I already changed the SPICE options from Default to Settings for better convergence but I´m still getting the same error.

Here is the circuit I am trying to simulate , where Vpp is a 12 V rail and FV is the output of the LM2907
Here is my circuit

This is the error log:

[SPICE] Gmin step [61 of 120] failed: GMIN=2.76482e-007

[SPICE] Gmin stepping failed

[SPICE] Source step [0 of 120] failed: source factor = 0.0000

[SPICE] Too many iterations without convergence.

Real Time Simulation failed to start.

Best Answer

I know this question is a little bit old, but I faced exactly the same problem, and finally, I found a solution and maybe it can help others.

I think the problem is the start state of the circuit and the SPICE simulator can not solve the internal equations in some specific situations, it's the same with symmetric astable multivibrator, we have to force an unbalanced start state to allow the simulation to start.

For the LM2907 we can easily create this unbalanced state just by adding an inverter in its input port, like this:

enter image description here

The inverter makes no difference in the circuit once we are just getting the frequency.

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