Thevenin Equivalent graph ideas

I can't thank you all enough for your help in preparing lab experiences for my students this semester. The first set of submissions will be coming in tomorrow.

Quick question... I have a Thevenin Equivalent circuit with a variable load resistor. The ultimate goal is a load line graph with I versus V and negative R as the slope of the graph. Using your Parameter techniques, I was able to create graphs of I versus R and V versus R. The only way I can see to get to the final goal of I versus V is to use the Excel spreadsheet and download the graph outside of CircuitLab. Is there something that I'm missing or another process I could use?

Thanks as usual, Carol Strong

by strongc
September 30, 2020

Here are a couple of suggestions for drawing an I vs V graph. I replace RL with a current (or voltage) source.

The DC Sweep Sim is set up for the left hand circuit, current control. There is an alternative voltage control version on the right (you will have to change the Sweep parameters in order to graph it).

The custom values (current or voltage) are arbitrary. For simplicity I have chosen ones that fall between RL as short- and open-circuit. The graphs show a slope of 200mV per 6mA, or 33 Ohm. The slope is negative because the sim is measuring current out of Rth as +ve.

Pushing the Thevenin concept further, you could select current values outside the circuit's natural range, eg -/+2A (custom values: -2,2). In this case the graph changes 100V per 3A, or 33 Ohm.

by EF82
October 20, 2020

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