Basic Elec. Engr. Lab
ECS 204
Dr. Prapun Suksompong
prapun@siit.tu.ac.th
1
Lab 2
 Thevenin’s and Norton’s Theorem
 New toy: Potentiometer
 Building a “fake” current source
2
Lab 2: Circuit under consideration
A
R1
330 ohms
B
R2
470 ohms
Vps
12V
RL
1200 ohms
C
D
(A.4)
R3
330 ohms
IL
E
3
Outline of the lab
Part A
RTH
C
A
R1
B
RL
VTH
IL
R2
Vps
D
C
C
RL
R3
IL
IN
RN = RTH
RL
IL
D
D
4
Part B
Part A: Thevenin Equivalent (1)
Part A
RTH
C
A
R1
B
VTH
IL
R2
Vps
D
C
VTH
RL
R3
IL
R3

V ps
R1  R2  R3
(A.12) C
RL
RTH IN R3 / /  R1  R2 R N = RTH (A.13)
D
IL 
5
RL
VTH
RTH  RL
(A.14) D
IL
Part A: Thevenin Equivalent (2)
Part A
RTH
C
A
R1
B
VTH
IL
R2
Vps
RL
D
C
C
RL
R3
IL
D
Directly measure VTH (A.5) and RTH (A.8)
Build simplified
circuitRNto= measure
RTH
RL I L
IN
IL
(A.11)
D
6
Part B: Norton Equivalent
RN  RTH
A
IN 
R1
B
R1  R2
RN
IL 
IN
RL  RN
C
(B.6)
RL
VTH
R2
Vps
V ps
RTH
(B.7)
IL
D
C
C
RL
R3
IL
IN
RN = RTH
RL
IL
D
D
7
Part B
Part B: Norton Equivalent
RTH
C
A
R1
Directly measure IN (B.2)
Build simplified
circuit to measure
IL (B.5)
R
V
B
L
TH
IL
R2
Vps
D
C
C
RL
R3
IL
IN
RN = RTH
RL
IL
D
D
8
Part B
Lab 2: Summary
Part A
RTH
(A.14)
(A.11)
C
A
R1
B
RL
VTH
IL
R2
Vps
D
C
C
RL
R3
IL
D
(A.4)
IN
RN = RTH
RL
IL
D
9
Part B
(B.7)
(B.5)
Need resistor whose value can be
adjusted arbitrarily
Lab 2: Summary
Part A
RTH
(A.14)
(A.11)
C
A
R1
B
RL
VTH
IL
R2
Vps
D
C
C
RL
R3
IL
D
(A.4)
IN
RN = RTH
RL
IL
D
10
Need current source
Part B
(B.7)
(B.5)
Potentiometer (Pot)
11
Pot as a variable resistor
 Manually adjustable resistor
 Three terminals
 The resistance between the middle terminal and either of the
two sides depends on the position of the wiper.
12
Current source
 We do not have current source.
 Again, it is meaningless to connect an ammeter directly across
the power supply. This will NOT give you the amount of
current produced by the power supply.
 We use a voltage source (power supply) to give the specified
amount of current.
C
IN
RN = RTH
VPS
RL
IL
D
13
A1
A2
IN
IL
R = RN
(RN = RTH)
RL
1200
ohms