I found a circuit simulator, QUCS. It looks very complete but I can't figure out how to make graphs with it. No matter what I do, I won't get a graph. For example if I select a resistor and connect it to an ac voltage source, I can't get it to give me the sine graph.
Any help?
get a
voltage
First click on this link:
Click on the "Free SwitcherCAD Download" button.
I tried that, but its simulator seems a bit off:
The time constant for your circuit is 10nS, so all the interesting stuff will happen in the first 50nS or so.
Go to the Simulate menu and select Edit Simulation Command. Set:
Stop Time 100ns Time to Start Saving Data 0ns Maximum Timestep 1ns
Next, left-click on the voltage supply and choose the PWL function. This will allow you to simulate turning on the power at a specified time. Set:
time1[s]: 0 value1[V): 0 time2[s]: 1ns value2[V]: 1V
Try that and see what happens.
Thanks, it works now. But shouldn't it work without the need to use a PWL? Even if I just use a voltage source?
Well, if the simulation assumes that the voltage source is fixed for all time (right back to -infinity), then the circuit will already be at steady state at t=0.
The simulator settles out the DC voltages before starting a transient run. So the cap is actually fully charged at time=0. One way to see the CR rise is to click on the ".op" button and type ".ic v(n002)=0". (lay the text somewhere on the circuit) This forces the 'Initial Condition' of circuit node#2 (the cap-resistor junction) to start at 0V at the time=0 point. john
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