Simulation pitfalls

From IBF-Wiki

Some simulation pitfalls are not detectable by the system.
Please take some seconds for this article.
You should not be untroubled by these traps.




  • Powersymbols 5Vref.png do not supply any voltage! You have to connect a voltage source to your e.g. +5V circuit.

further details




  • FALSE: My circuit includes alternating (sinusoidal) current sources Sinus source ieee.png, so i have to apply an ac-analysis.
It is quite simple:
My abscissae (x-coordinate) of the oscilloscope shall be the time => Transientanalysis
My abscissae (x-coordinate) of the oscilloscope shall be the frequency => AC-Analysis
My abscissae (x-coordinate) of the oscilloscope shall be a voltage => DC-Analysis

further details




  • Not connected components (a tiny red cross indicates the error)! Not connected en.png
    Pins are connected via (green) signal lines; so do not simply join pins.




  • I do not see any rc charge curve? Uic 1 en.png Uic 2 en.png
    Only if you select (default) Uic 3 en.png in the transient analysis dialog, then the curve will be there.

further details




  • What is a capacitor? What a dull question! Edit capacity value and play up simulation: Oops, what's that? The simulator shows (apparently) absurd curves or error messages. Result of a fallacy! You apply only a model of the capacitor. Surely you can use a very ideal capacitor model, carrying only the capacitance as quantity, but: A model which is closer to a real capacitor has an additional serial resistor, so that e.g. charge-time/current-peaks of a unit step input response Ideal en.png do not get arbitrary small/high values. You should ever ask yourself:
    Is my model of this component too ideal for my application case?











Further Details:



Supply

1) A reference symbol is only a drawing aid. It allows to design the schematic in a well arranged manner and to spread the circuit over multiple sheets.
2) What should +5V stand for? Is it a 1W (one watt) or a powerfull 100W source? Your circuit would work fine with an ideal source, but your real application could suffer power stability showing bizarre effects.


Types of simulation analysis

The selection of the appropriate analysis do not depend on the sources that your circuit contains. You will find further graphical explenation in the respective analysis dialogs.


Initial conditions

The simulator has to find a first bias point (solution) for time t=0. Some components are provable with an initial state: e.g. you can define that a capacitor is charged to 5V at time t=0. If you do not select "Use initial condition" then the simulator will calculate only one (initial)solution of many with any initial states of the capacitors etc.; viz. the steady state, that is after all capacitors in your real application are settled.


















































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