Sample Simulation Run: Week Four
Thevenin's Theorem and Max Power Transfer

For the circuit shown below, the current through R(L) and the voltgae across R(L) can be calculated easily. If R(L) changes in value, your entire solution must be reworked.

Thevenin theorem will help solve this problem as it offers a solution that is independent of R(L).

Practical Application of Thevenin's Theorem

For the Bridged-tee circuit shown below, find the Thevenin equivalent for the circuit external to R(L).

sample week 4b

Please Note:
You need to have the PSpice computer simulation program on board, and linked to your Web browser in order to run the simulation on-line. This will generate output file(s), including plots and graphs.

Thevenin Analysis of Bridged-Tee Circuit
V   1 0 80V
R1  2 1 20
R2  2 3 100
R3  3 0 200
R4  3 4 100
R5  2 4 400
R6  4 0 1E12
.OP
.TF V(4) V
.OPTIONS NOPAGE
.END

NOTES:
Instead of simply removing R(L), we should replace it with a very large load resistance, say R(L)=1 tetraohm (1E12).

PSpice Simulation Results


**** 08/17/96 21:52:25 ********* NT Evaluation PSpice (April 1995) ***********
 Thevenin Analysis of Bridged-Tee Circuit
  ****     CIRCUIT DESCRIPTION
  ******************************************************************************
  V  1 0 80V
  R1 2 1 20
  R2 2 3 100
  R3 3 0 200
  R4 3 4 100
  R5 2 4 400
  R6 4 0 1E12
  .OP
  .TF V(4) V
  .END

  **** 08/17/96 21:52:25 ********* NT Evaluation PSpice (April 1995) ***********
   Thevenin Analysis of Bridged-Tee Circuit
    ****     SMALL SIGNAL BIAS SOLUTION       TEMPERATURE =   27.000 DEG C
 ******************************************************************************
 NODE   VOLTAGE     NODE   VOLTAGE     NODE   VOLTAGE     NODE   VOLTAGE
 (  1)   80.0000  (    2)   74.7250  (    3)   52.7470  (    4)   57.1430  

    VOLTAGE SOURCE CURRENTS
    NAME         CURRENT
     V           -2.637E-01

  TOTAL POWER DISSIPATION   2.11E+01  WATTS

 **** 08/17/96 21:52:25 ********* NT Evaluation PSpice (April 1995) ***********

Thevenin Analysis of Bridged-Tee Circuit


****     OPERATING POINT INFORMATION      TEMPERATURE =   27.000 DEG C
******************************************************************************
****     SMALL-SIGNAL CHARACTERISTICS

      V(4)/V =  7.143E-01
      INPUT RESISTANCE AT V =  3.033E+02
      OUTPUT RESISTANCE AT V(4) =  1.286E+02

               JOB CONCLUDED
               TOTAL JOB TIME             .08

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[IMPLEMENTATION]

Maximum Power Transfer Theorem

sample week 4c

Maximum Power Transfr
V  1 0 12V
R1 1 2 20
R2 2 0 20
R3 2 3 20
RL 3 0 RLOAD 1
.MODEL RLOAD RES
.DC RES RLOAD (R) 10 40 2
.option nopage
.PRINT DC V(RL) V(R1) 
.PLOT DC V(RL)  V(R1)
.PROBE
.OP
.END

NOTES:

One of the important advantages of the probe option is that a specific variable can be plotted or a quantity determined by a mathematical operation. In this case, we request to plot V(3)*V(3)/R to find out for what value or RLOAD the max power is transferrd.
The .MODEL command is used to specify specific characteristics about the element (tolerance, temperature coefficient, ...).
The command is required if R(L) is to be varried between specific limits.
The next command specifies the variable to be varied between the limits indicated on the same line.
.PRINT statement specifies quantities to be output.
.PLOT DC command requests that the data for the above be plotted for the range of R(L) values.

PSPICE OUTPUT FILE

**** 08/24/96 17:47:54 ********* NT Evaluation PSpice (April 1995) ***********
Maximum Power Transfer to R Load
 ****     CIRCUIT DESCRIPTION
******************************************************************************
V  1 0 12V
R1 1 2 20
R2 2 0 20
R3 2 3 20
RL 3 0 RLOAD 1
.MODEL RLOAD RES
.DC RES RLOAD (R) 1 30 2
.option nopage
.PRINT DC V(RL) V(R1) 
.PLOT DC V(RL)  V(R1)
.PROBE
.OP
.END
 ****     Resistor MODEL PARAMETERS
               RLOAD           
           R    1            
 ****     DC TRANSFER CURVES               TEMPERATURE =   27.000 DEG C
  R           V(RL)       V(R1)       

   1.000E+00   1.935E-01   7.935E+00
   3.000E+00   5.455E-01   7.818E+00
   5.000E+00   8.571E-01   7.714E+00
   7.000E+00   1.135E+00   7.622E+00
   9.000E+00   1.385E+00   7.538E+00
   1.100E+01   1.610E+00   7.463E+00
   1.300E+01   1.814E+00   7.395E+00
   1.500E+01   2.000E+00   7.333E+00
   1.700E+01   2.170E+00   7.277E+00
   1.900E+01   2.327E+00   7.224E+00
   2.100E+01   2.471E+00   7.176E+00
   2.300E+01   2.604E+00   7.132E+00
   2.500E+01   2.727E+00   7.091E+00
   2.700E+01   2.842E+00   7.053E+00
   2.900E+01   2.949E+00   7.017E+00

 ****     DC TRANSFER CURVES               TEMPERATURE =   27.000 DEG C
 LEGEND:
*: V(RL)
+: V(R1)

  R           V(RL)       
(*)----------    0.0000E+00   1.0000E+00   2.0000E+00   3.0000E+00   4.0000E+00
(+)----------    6.5000E+00   7.0000E+00   7.5000E+00   8.0000E+00   8.5000E+00
                       _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  1.000E+00  1.935E-01 .  *         .            .          + .            .
  3.000E+00  5.455E-01 .      *     .            .       +    .            .
  5.000E+00  8.571E-01 .          * .            .     +      .            .
  7.000E+00  1.135E+00 .            . *          .  +         .            .
  9.000E+00  1.385E+00 .            .    *       .+           .            .
  1.100E+01  1.610E+00 .            .       *   +.            .            .
  1.300E+01  1.814E+00 .            .         +* .            .            .
  1.500E+01  2.000E+00 .            .        +   *            .            .
  1.700E+01  2.170E+00 .            .      +     . *          .            .
  1.900E+01  2.327E+00 .            .     +      .   *        .            .
  2.100E+01  2.471E+00 .            .    +       .     *      .            .
  2.300E+01  2.604E+00 .            .  +         .       *    .            .
  2.500E+01  2.727E+00 .            . +          .        *   .            .
  2.700E+01  2.842E+00 .            .+           .          * .            .
  2.900E+01  2.949E+00 .            +            .           *.            .
                       - - - - - - - - - - - - - - - - - - - - - - - - - - - 

 ****     SMALL SIGNAL BIAS SOLUTION       TEMPERATURE =   27.000 DEG C

 NODE   VOLTAGE     NODE   VOLTAGE     NODE   VOLTAGE     NODE   VOLTAGE
(    1)   12.0000  (    2)    4.0645  (    3)     .1935  

    VOLTAGE SOURCE CURRENTS
    NAME         CURRENT

    V           -3.968E-01

    TOTAL POWER DISSIPATION   4.76E+00  WATTS

 ****     OPERATING POINT INFORMATION      TEMPERATURE =   27.000 DEG C
          JOB CONCLUDED
          TOTAL JOB TIME             .19

Graphical Representation using Probe