Problem 5.5 - PSpice Solution for a Thevenin Equivalent Circuit
*
* The circuit for this problem is from textbook Chap. 5, Problem 13.
*
* NOTE: This is a four-part problem:
* 1. Find the open circuit voltage V(3) for the circuit as given.
* 2. Find short circuit current by adding a zero-volt source at node
* 3. Hand-calculate the Thevenin equivalent circuit resistance.
* 3. Connect a variable load resistance to the original circuit using
* the .MODEL command. (See the circuit description entry for R3.)
* Use PROBE to graph a curve of power delivered to the load.
* 4. Connect the same variable load resistance to the Thevenin
* equivalent circuit. Graph a curve of power delivered to the load.
*
* The three end-to-end programs below will obtain in one program run
* the separate solutions to Parts 1, 2, and 3 as given above.
*
* IMPORTANT: Run Parts 1 and 2 and obtain the results before trying
* to enter data for Parts 3 & 4. Parts 3 & 4 can only be run after
* an initial program run (of Parts 1 & 2) is complete and the
* Thevenin equivalent voltage and resistance are known.
* The program can then be re-run and the two PROBE graphs obtained
* either as separate graphs or with both graphs on one page.
*
* The solution graph shown in this manual was obtained by selecting
* "All_Dc_sweep" on the PROBE menu screen and then entering the
* expression V(3)*I(R3) for Part 3 and the expression V(2)*I(R2)
* for Part 4 on one graph. This assumes that the output node of
* your Thevenin circuit in Part 4 is node 2 and that the load
* resistance is named R2.
*
.OPT NOPAGE NUMDGT=6
V1 1 0 DC ??? ; Enter the value of voltage source V1.
G1 2 3 ??? ??? 2 ; Enter + and - nodes of the control voltage.
R12 1 2 15
R2 2 0 10
R23 2 3 20
.DC V1 ; Complete the .DC sweep command statement.
.PRINT DC V(3) ; Or you could use the .OP command instead.
.END
Problem 5.5, Part 2. PSpice Solution for a Thevenin Equivalent Circuit
*
* Add a zero-volt source across output terminals to determine
* the short circuit current of the network. Calculate resistance.
*
.OPT NOPAGE NUMDGT=6
V1 1 0 DC ??? ; Enter the value of voltage source V1.
V2 3 0 DC 0
G1 2 3 ??? ??? 2 ; Enter + and - nodes of the control voltage.
R12 1 2 15
R2 2 0 10
R23 2 3 20
.DC V1 ; Complete the .DC sweep command statement
; Use a .PRINT statement to obtain the
; short circuit current at node 3.
.END
Problem 5.5, Part 3. PSpice Solution for a Thevenin Equivalent Circuit
*
* Attach a variable resistance value as a load on the original
* circuit, and print out the load current values over resistance
* range.
* See .MODEL command in Appendix B of the PSpice manual for further
* information on the use of .MODEL to create a variable resistance.
* Use PROBE to obtain a graph of the expression for the power
* delivered to the load as a function of the resistance value.
*
.OPT NOPAGE NUMDGT=6
V1 1 0 DC ??? ; Enter the value of voltage source V1.
G1 2 3 ??? ??? 2 ; Enter + and - nodes of control voltage.
R12 1 2 15
R2 2 0 10
R23 2 3 20
R3 3 0 RLOAD 1 ; Resistance with model named RLOAD and
; a model parameter multiplier of 1.
.MODEL RLOAD RES(R=25) ; Model with resistance parameter = 25,
.DC RES RLOAD(R) 25 500 25 ; "dc sweep" of a model of type=RES, and
; model name=RLOAD. The model parameter
; R is swept from 25 to 500 ohms in
; increments of 25 ohms per step.
.PROBE I(R3) V(3) ; Enables the graphics post-processor.
.PRINT DC I(R3) V(3)
.END
* Problem 5.5, Part 4. PSpice Solution for a Thevenin Equivalent Circuit
*
* Construct a Thevenin equivalent circuit, and attach the variable
* resistance load as in Part 3. Run PSpice analysis and compare
* results. Include PROBE statement. Print I(R3) and V(3) as in
* Part 3 above.
*
* A second PROBE data file will be created. When running PROBE you may
* view the files consecutively or superimposed. Follow the PROBE menu.
*