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ELEC195 LAB #8 2/6/03 J. F. Santacroce

NAME:______
ELEC195 CIRCUIT THEORY II
PARTNERS:______
______
DATE:______

LAB #8 THEVENIN’S THEOREM

OBJECTIVE:
To calculate the load voltage and load current using Thevenin’s Theorem.
To verify your results by using Pspice simulation to verify the load voltage and load current for the circuit.
EQUIPMENT: /

PARTS & SUPPLIES

HP-33120A Function Generator

HP-54600 Oscilloscope

/ 1 – 100 , ¼ W Resistor
1 – 220 , ¼ W Resistor
HP-34401A Multimeter / 1 – 330 , ¼ W Resistor
1 - Analog Breadboard / 2 – 0.1 uF, Capacitors
1 - CDA 3 Decade Capacitor Box / 1 – 0.047 uF, Capacitor
1 - CDA 5 Decade Capacitor Box
1 – Resistor Decade Box / 1 Sets Banana to Alligator Clip Leads
2 Sets BNC to Alligator Clip Leads
1 Set BNC to Alligator Clip Leads( Blue Band).

DISCUSSION:

The series-parallel circuit shown in Figure #1 is to be analyzed using Thevenin’s Theorem. During this experiment you will measure Thevenin’s equivalent circuit and subsequently verify your results using Pspice.

Thevenin’s equivalent voltage directly measured as the open-circuit voltage with the load capacitor, CL removed. Thevenin’s equivalent impedance will be calculated by first measuring the following parameters; vOC (open-circuit voltage) and iSC (short-circuit current) and then satisfying the equation given below:

ZTH = vOC / iSC

SCHEMATIC:

Figure #1

REQUIRED EQUATIONS:

ZTH = vOC / iSC

Z1 = R1 + jXC1

Z2 = R2 + jXC2

Z3 = R3

ZL = CL

PROCEDURE:

1. Construct the circuit shown in Figure #1. Set the HP-33120A Function Generator to a 5VRMS (sine wave) with the frequency at 16kHZ.

Measure the required circuit parameters, in polar form, as required in the following table.

e = ______(polar form) / vL = ______(polar form)
iL = ______(polar form)
VOC = ______(polar form) / iSC = ______(polar form)

2. Construct Thevenin’s Equivalent circuit using both the Decade Resistor Box and the Decade Capacitor Box and measure:

vL = ______(polar form) / iL = ______(polar form)

3. Calculate the following circuit values:

XC1 = XC2 ______(polar) / XC1 = XC2 ______(rectangular)
Z1 = ______(polar) / Z1 = ______(rectangular)
Z2 = ______(polar) / Z2 = ______(rectangular)
Z3 = ______(polar) / Z3 = ______(rectangular)
ZL = ______(polar) / ZL = ______(rectangular)
ZTH = ______(polar) / ZTH = ______(rectangular)
eTH = ______(polar) / *iN = ______(polar)
vL = ______(polar) / iL = ______(polar)

*Norton’s equivalent

PSPICE VERIFICATION:

The remainder of this experiment is to be performed using Pspice in conjunction with Thevenin’s Theorem to verify the measured results.

1. Simulate the entire circuit of Figure #1 and solve for vL across CL. Please note that Pspice needs a dc-path from every node to ground. Therefore, place a 100 Meg- resistor across the output to ground as part of your simulation set-up. Measure vL by placing VPRINT1 at the node above CL.

Set the following parameters;

VSIN:VPRINT1:

DC=0DC=0

AC=5VAC=?

VOFF=0MAG=ok

VAMPL=5VPHASE=ok

FREQ=16.0KHZIMAG=ok

TD=0REAL=ok

ANALYSIS SETUP:TRANSIENT SETUP:

ACSWEEP;PRINT STEP 5us

TOTAL PTS 1FINAL TIME 200us

STARTFREQ 16KHZ

END FREQ 16KHZ

2. Using the techniques of Part 1, find Thevenin’s equivalent voltage. This is the open-circuit voltage and don’t forget the 100Meg- resistor to ground.

3. Find Thevenin’s equivalent impedance using the relationship:

ZTH = vOC / iSC.

Therefore, find iSC by using Pspice and placing a short-circuit across the output. This is accomplished by using IPRINT as the short!

4. Build up Thevenin’s circuit by using the real part of ZTH as RTH and the imaginary part as XTH , the reactance of CTH. Calculate the capacitor value from this reactance! Put the 0.047uF capacitor back as the load and simulate the output voltage.

5. Compare the simulated results with the measured results.