Re: Convergence problem with Sallen-Key filter circuit
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Jan wrote, "The initial operating point solution does not converge.?"
Actually, it does.? But the Gmin Stepping algorithm has trouble, and either runs a very long time or never finishes.? We see this from time to time.? I don't know why LTspice seems to get stuck on one algorithm instead of moving on, but it happens occasionally.
LTspice has a handful of different algorithms that it tries when looking for the DC operating point.? It's supposed to know when one isn't working, and move on to try the next, and so on.? In your circuit's case, the Direct Newton-Raphson Iteration algorithm quickly fails, and then the Gmin Stepping algorithm tries but seems to keep trying forever.? So you need to tell LTspice to skip that algorithm:
? ? .options GminSteps=0
I see that you had that on your schematic, but it is commented out (ineffective).
Alternatively, you can press the Esc key when it's trying (forever) in that algorithm, and it moves on to the next one.? Watch the status messages in the lower left corner.? "Press Esc to quit" doesn't quit LTspice; it only quits the current algorithm.? Your circuit converges OK with either the Source Stepping or the Pseudo Transient algorithms.
See this Help page: LTspice > Dot Commands > .OP -- Find the DC Operating Point
Regards, Andy
Hello there group members,
I'm trying to simulate a Sallen Key filter with a cutoff frequency of around 40kHz using a unipolar 5V source (See TEMP section). The initial operating point solution does not converge.?
I have added series resistances everywhere so?every point in the circuit has a connection to GND as described in?
Since I cannot find any problem in my circuit, I'm out of ideas on where LTSpice might fail.?
Can someone hint me to where the problem might be?
?
Best regards,
Jan
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