EAST WEST UNIVERSITY
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING
COURSE NO: EEE 101
EXPT: 07
Circuit analysis in PSPICE using source and resistance sweep
OBJECTIVE
In this lab, DC analysis of circuits will be performed by sweeping DC sources and resistance.
Application of resistance sweep will also be used to study the maximum power transfer
theorem.
INTRODUCTION
SPICE allows different types of analysis, such as, DC analysis, AC analysis, Transient
analysis etc. DC analysis may be performed by varying the value of an independent DC
voltage or current source or by varying a resistance. The results of such sweeps may be
graphically viewed using the Probe tool of PSPICE.
CIRCUIT DIAGRAM
Vx
+
Fig. 1
PROCEDURE
1. Draw the circuit of Fig. 1 in Schematics and simulate the circuit to determine the open
circuit voltage Voc between nodes 5 and 0. Note that PSPICE gives error if one end of an
element (R5 in this case) remains unconnected. This problem can be overcome by
connecting a 0A current source between nodes 5 and 0.
2. Connect nodes 5 and 0 of Fig. 1 through a short circuit and simulate the circuit to
determine the short circuit current Isc flowing from node 5 to node 0. Calculate Vth and Rth
for Fig. 1 from the simulations performed in steps 1 and 2.
3. Remove the short circuit between nodes 5 and 0. Connect a 10 Ohm resistance RL between
these two nodes. In the Analysis Setup dialog box, click the DC Sweep button. Select Linear
type and Voltage source as a sweep variable. Write V1 as a sweep variable name with Start
value = 0V, End value = 20V and Increment = 1V. Simulate the circuit. If simulation is
successfully completed, a Probe window will appear with V1 being the x-axis. Click Add
Trace in Probe window and select V(3) and V(5). Add another plot to the window and add
I(R5). From the plots using the cursor, determine the values of V(3), V(5) and I(R5) at
V1=10V.
4. In this step, we will vary the resistance RL and observe circuit variables as functions of
RL. The following lists how a simulation is done by resistance sweeping.
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a. Double-click the value label of the resistor, RL which is to be varied. This will
open a Set Attribute Value dialog box. Enter the name {RVAR} (including the
curly braces) in place of the component value. Choose Get New Part from the
menu and select the part named param.
b. Place the box anywhere on the schematic page. Double-click on the word
PARAMETERS in the box title to bring up the parameter dialog box. Set the
NAME1= RVAR (without the curly braces), which is the same name given to the
resistor to be varied, and the VALUE1= 10 (or any other arbitrary value).
c. In the Analysis Setup dialog box, click the DC Sweep button and select Linear type and
Global Parameter as a sweep variable. Type RVAR as a sweep variable Name
with Start value = 1, End value = 20 and Increment = 0.1. Simulate the circuit and if
simulation is successful, a Probe window will appear with RVAR being the x-axis.
d. Click Add Trace in Probe window and select V(3) and V(5). Add another plot to
the window and add I(R5). From the plots using the cursor, determine the values
of V(3), V(5) and I(R5) at RL=10 Ohm. Compare these values with those
obtained in step 3.
e. Delete the existing plots and select I(R5)*I(R5)*RVAR for plot as a function of
load resistance. Note that I(R5)*I(R5)*RVAR represents the load power.
Determine the maximum value of the load power and the value of load
resistance for which the load power is the maximum. How does this value
compare with Rth of the circuit?
6. Copy the simulated circuits corresponding to steps 1 and 2 to a MS-Word file. Next copy
the Probe plots corresponding to steps 3, and 4 (two plots for step 4) to a MS-Word file. In
each case, there should be two figures per plot. Print the results and have the printouts signed
by the instructor.
PRE-LAB REPORT QUESTIONS:
1. Theoretically determine the Thevenin’s equivalent circuit for Fig. 1.
2. Calculate V(3), V(5) and I(R5) for RL=10 ohms. RL is to be connected between nodes 5
and 0.
3. Calculate the value of RL for maximum power condition and the maximum power that
may be delivered to this RL. Note that the voltages and the currents are indicated in Fig.
1.
POST-REPORT QUESTIONS:
1. Submit the signed printouts of the PSPICE simulation results.
2. Compare the theoretical solutions with the solutions obtained from PSPICE and comment.
3. What are the possible applications of DC sweep of PSPICE? Mention one application
where a DC voltage sweep is useful and one application where a DC resistance sweep is
useful.
4. How can the maximum power transfer theorem be used to determine the Thevenin’s
equivalent resistance of a circuit? Briefly discuss.
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