In our second PSpice lab, we used the schematic input method to compute Thevenin voltages, Thevenin resistances, Norton currents, and maximum power wattage.
First, we practiced building a circuit and probing for current and voltage values. This just required the placement of the individual elements and viewpoints.
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| Click for larger |
Next, we used PSpice to calculate the Thevenin and Norton equivalents for a different, more complicated circuit. We drew up the circuit in Schematic and replaced the element we're finding Vth with respect to with a current supply. We then set up a simulation to "sweep" (or vary) the current over a set of values and plot the results. The 20V corresponding to a current of 0A (the y-intercept) is our Vth; the slope of our line, 6 Ohms is Rth (because R=V/I).
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| Replacing the load with a current supply to find Vth |
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| Thevenin voltage is the intercept; Thevenin resistance is the slope (click for larger) |
Norton current can be found by replacing the current supply with a voltage supply and sweeping the voltage. The 3.33A corresponding to a voltage of 0V is our In.
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| Norton current is the intercept; Thevenin resistance is the inverse of the slope (click for larger) |
Armed with Thevenin and Norton values, we drew up an equivalent circuit in order to find the maximum power dissipated across a load resistor. We used the parameter table to create a resistor that is swept across a series of values. After simulating, we plotted voltage*current and looked for the maximum. The y-value (250mW) was our maximum power, and the x-value was the corresponding load voltage that gave us this max power (it was equivalent to Rth, which was expected).
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| Maximum power (click for larger) |
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