Thevenin, Norton and Maximum
Power Transfer Theorems

Why Thevenin’s Theorem is useful

Everything in the original circuit, except the
load, may be replaced by an equivalent circuit.
The equivalent circuit consists of a series
combination of a voltage source and a
resistance.
Write these on white board
VTH = 10V
RTH = 5kΩ
Now you can place any load in the circuit you
want and the calculations are EASY!
.66mA
=10kΩ
Determine VTH
Solving for VTH
10V
5V
VTH = VA – VB = 5V
Determine RTH
What is the resistance from point a to b?
Be careful, since 20V
is upside down VA is
across R1


http://www.youtube.com/watch?v=SWWt9I
C7mGs&NR=1&feature=fvwp
https://www.facebook.com/photo.php?v=133
641650156241

Everything in the original circuit, except the
load may be replaced by an equivalent circuit.
The equivalent circuit consists of a parallel
combination of a current source and a
resistance.
Norton Current IN
2mA
Norton
Resistance

There are a bunch of rules for how to calculate the
Norton Current and Norton Resistance. However,
a shortcut is to find the Thevenin Equivalent
circuit and then convert it to a Norton
2mA

Besides using traditional circuit analysis using
Ohm’s Law, or Superposition, Mesh Analysis,
Thevenin’s Theorem, and Norton’s Theorem,
there are other circuit analysis techniques. A
couple include:

Nodal Analysis and Millman’s Theorem
Do more hw problems from back of chap
12 (9, 10, 11, or 12) if time

In the following circuit solve for
VTH, RTH, IN, RN, IL and VL
Solve for VL using traditional Ohm’s Law
technique, Mesh Analysis, and Thevenin Analysis

See notes (Draw 5 circuits)
RL (Ω)0
VT (V)
I (A)
PL(W)
Pi (W)
PT (W)
Eff (%)
0
0
20
0
2000
2000
0
1
16.7
16.7
278.9
1394
1673.4
16.7
2
28.6
14.3
409
1022
1431.5
28.6
3
37.5
12.5
468.8
781.3
1250.1
37.5
4
44.4
11.1
492.8
616.1
1108.9
44.4
5
50
10
500
500
1000
50
6
54.5
9.1
496
414.1
910.05
54.5
7
58.3
8.3
483.9
344.5
828.35
58.3
8
61.6
7.7
474.3
296.5
770.75
61.6
9
64.3
7.1
465.5
252.1
717.55
64.3
10
66.7
6.7
446.9
224.5
671.35
66.7
20
80
4
320
80
400
80
30
85.7
2.9
248.5
42.05
290.55
85.7
40
88.9
2.2
195.6
24.2
219.8
88.9
50
90.9
1.9
172.7
18.05
190.75
90.9
?
What circuit analysis technique can we use to solve for this?
Thevenin’s Theorem.
RTH = 5kΩ
I’ve checked this technique using Ohm’s law and it works. See following numbers:
5mW @ 5kOhm
4.94mW @ 4kOhm
4.96mW @ 6kOhm
SPST
SPDT
DPST
DPDT