İzmir University of Economics
EEE 432 Measurement and Instrumentation Lab
EXPERIMENT 1
Thevenin’s Equivalent and
Maximum Power Transfer
A. Background
A.1. Thevenin’s Equivalent Circuit
In 1883, a French telegraph engineer Léon Charles Thévenin stated
a theorem on the equivalent circuit representation of a complex
circuit using a voltage source connected in series with a resistor.
Consider a circuit having several components such as voltage
sources (VSi’s), current sources (ISj’s), resistors (R’s). Thévenin’s
theorem states that the equivalent circuit seen from the output port
can be represented using just two components: (i) A voltage source
(Vth) and (ii) a resistor (Rth) (Fig. 1.1).
I
I
+
VSi
ISj

V
R
-
+
Rth
Vth
V
-
Fig. 1.1
The original circuit and the Thevenin’s equivalent have the same V-I relationship as
specified at the output terminals. Thevenin’s equivalent circuit is indeed a virtual
circuit that is used to simplify the circuit analysis.
Consider the circuit given in Fig. 1.2a. Assume its Thevenin’s equivalent is as given in
Fig.1.2b.
I
I
+
R1
R2
VS
V
-

(a)
Rth
Vth
+
V
-
(b)
Fig. 1.2
1-1
The components Vth and Rth that will result in the same terminal V-I characteristics
may be obtained easily (see class notes). Vth is simply the voltage observed between
the output terminals. Several techniques may be used to determine Vth. For the circuit
given in Fig. 6.5, the Thevenin’s voltage Vth can be obtained easily using voltage
division as :
Vth
R
R
R
V
and Rth is the equivalent resistor seen from output terminals when all sources are set
to zero. So when VS = 0 V in the circuit of Fig. 6.5a,
Rth
R
R
Thevenin’s theorem help us to simplify the circuit analysis.
A.2. Maximum Power Transfer
Maximum Power Transfer Theorem states that an independent voltage source VS in
series with a resistance RS (Fig. 1.3) delivers a maximum power to that load
resistance RL for which RL = RS.
IL
+
RS
RL
VS
VL
-
Fig. 1.3

1-2
B. Preliminary Work
B. 1. Consider the circuit given below in Fig. 1.4. Determine the Thevenin’s
equivalent seen from the terminals A & B.
Vth, Rth
R1
VS
VS = 10 V
R1 = 12 K
R2 = 15 K
R3 = 3.9 K
R4 = 10 K
R3
R2
Circuit Parameters
R4
Fig. 1.4
B. 2. Repeat B.1 if VS = 10 sin 2f0t volts where f0 = 1 kHz.
B. 3.
uggest a method to determine the Thevenin’s equivalent circuit parameters of
a circuit containing constant voltage/current sources and resistors, using only a
multimeter.
B. 4.
uggest a method to determine the Thevenin’s equivalent circuit parameters of
a circuit containing sinusoidal voltage/current sources and resistors, using only
a multimeter.
B. 5. Assume a resistor RL is connected between the terminals A&B over the over the
circuit given above (Fig. 1.5),
(i) Determine the value of the load resistor RL to be connected between the
output terminals A&B so that the power delivered to the load RL is
maximum.
(ii) Determine also the maximum power dissipation over RL.
Circuit Parameters
R1
VS
R3
R2
R4
RL
VS = 10 V
R1 = 12 K
R2 = 15 K
R3 = 3.9 K
R4 = 10 K
Fig. 1.5
B. 6. Repeat B.5 if VS = 10 sin 2f0t volts where f0 = 1 kHz.
1-3
C. Experimental Work
C. 1.
Construct the circuit given below in Fig. 1.6. Determine the Thevenin’s
equivalent seen from the terminals A & B, using the method you suggested in
the Preliminary Work.
Vth, Rth
R1
VS
R3
R2
R4
Circuit Parameters
VS = 10 V
R1 = 12 K
R2 = 15 K
R3 = 3.9 K
R4 = 10 K
Fig. 1.6
C. 2.
Repeat C.1 if VS = 10 sin 2f0t volts where f0 = 1 kHz.
C. 3.
Now construct the circuit given below in Fig. 1.7. Connect 10 K potentiometer
as load resistor. Connect a voltmeter and an ampermeter as shown.
1-4
Circuit Parameters
R1
R3
VS
VS = 10 V
R1 = 12 K
R2 = 15 K
R3 = 3.9 K
R4 = 10 K
RL = 10 K pot
A
R2
V
R4
RL
Fig. 1.7
Vary RL between 0 and 10 K and measure VL and IL. Calculate PL and fill in the
following table. Plot PL as a function of RL.
RL
(k)
VL
(volt)
IL
(mA)
PL
(mW)
0
10
PL mW
RL, k
0
C. 4.
RL
(k)
VL
(volt)
IL
(mA)
PL
(mW)
1
2
3
4
5
6
7
8
9
10
Repeat C.3 if VS = 10 sin 2f0t volts where f0 = 1 kHz.
0
10
1-5
PL mW
RL, k
0
C. 5.
1
2
3
4
5
6
7
8
9
10
Comment on the findings and achievements you got from this experiment
1-6