Created by
Created April 08, 2012
Last modified June 11, 2012
Tags choosing-time-step   convergence   convergence-problem   opamp   relaxation-oscillator   startup  


An opamp based squarewave relaxation oscillator.


An opamp based squarewave relaxation oscillator.

i) Need to use opamp symbol/ model with supply rails and then add defined +ve and -ve supplies. ii) Use smaller time steps compared to simulation time. CircuitLab suggests using time steps at least 10 times shorter than the fastest signal in your simulation.

The slew rate of the LM741 is only about 1V/us and it is slewing several volts, so this would suggest that edges are quite slow; in times of us. However, internally to the opamp model there may be signals, particularly currents, that are changing much faster. Hence a much shorter time step is required. Choosing a timestep of about 1/(10*GBW) where GBW is the opamp gain bandwidth product (about 10^6 for the LM741) is probably a better starting point for opamp based switching circuits.

You can check the opamp GBW in the CircuitLab model properties by double clicking on the symbol.

Simulate > Time Domain > Run Time=Domain Simulation.


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