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EXPERIMENT 4
Thevenin’s And Norton’s Theorem
1.
OBJECTIVE:
1.1 To compare between analyze of complex circuit and Thevenin /Norton
equivalent circuit.
1.2 To learn concept of ideal current source.
2.
INTRODUCTION:
The Thevenin equivalent method allows you to replace any circuit consisting of
independent sources, dependent sources and resistors with simple circuit
consisting of a single voltage sources in series with a single resistor where the
simple circuit is equivalent to the original circuit. This means that a resistor first
attached to the original circuit and then attached to the simple circuit could not
distinguish between the two circuits, since the resistor would experience the same
voltage drop, the same current flow and thus the same power dissipation.
The Thevenin equivalent method can thus be used to reduce the
complexity of a circuit and make it much easier to analyze. A Norton equivalent
circuit consists of a single current source in parallel with a single resistor and can
be constructed from a Thevenin equivalent circuit using source transformation.
Thus in this section we will present a technique for calculating the component
values for a Thevenin equivalent circuit, if you want the Norton equivalent circuit,
you can calculate the Thevenin equivalent circuit and use source transformation.
There are three important quantities that make up a Thevenin equivalent
circuit, the open-circuit voltage, Voc, the short circuit current, isc and the Thevenin
equivalent resistance, RTh. In the Thevenin equivalent circuit, the value of the
voltage source is Voc and the value of the series resistor is RTh. In the Norton
equivalent, the value of the current source is isc and the value of the parallel
resistor is RTh but it is not necessary to calculate all three quantities, since they are
related by following equation:
Voc=RThisc
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(1)
Thus we need to determine just two of these three quantities and can use their
relationship to find the third quantity, if desired. In circuit containing only
independent sources and resistor, our Thevenin equivalent method will determine
the values of voc and RTh. When a circuit also contains dependent sources we will
modify the method and determine voc and RTh.
3.
COMPONENT AND EQUIPMENT:
3.1 Breadboard – 1 unit
3.2 DC power supply – 1 unit
3.3 Digital Multimeter – 1 unit
3.4 Wires
3.5 Resistors:
3.5.1 100 Ω resistor - 1 pcs
3.5.2 470 Ω resistor - 1 pcs
3.5.3 1.0 kΩ resistor - 1 pcs
3.5.4 1.5 kΩ resistor - 1 pcs
3.5.5 4.7 kΩ resistor - 1 pcs
3.5.6 33 kΩ resistor - 1 pcs
4.
PROCEDURE:
4.1 Thevenin’s Theorem:
4.1.1
Consider the circuit in Figure 4.1 .Find its Thevenin’s equivalent circuit.
Draw and label your circuit in Figure 4.4.
4.1.2
Build the circuit shown in Figure 4.1 on the breadboard mounted to the
bench top, using the DC power supply as vs. Once you have built the
circuit, set the value of vs to 10 V. Be sure to use the multimeter to
make sure the terminal voltage produced by the power supply is as
close to 10 V as you can get it.
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Figure 4.1
4.1.3
4.1.4
4.1.5
Schematic diagram of circuits.
Measure and record the voltage across a-b terminal. This is Thevenin
equivalent circuit voltage, voc.
Remove DC power supply from the circuit and disconnect its terminal.
Measure resistance across a-b terminal. Record its value as this is
Thevenin equivalent resistance, RTh.
Calculate the voltage drop across RL using this formula below:
VRL= vocRL
(2)
RTh +Rl
4.1.6
Connect RL and DC power supply back to the circuit. Turn on the power
supply, measure and record the voltage across RL (a-b terminal).
4.1.7
Repeat step 1 till 6 for circuit in Figure 4.2.
Figure 4.2
Schematic diagram of circuits.
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4.2 Norton’s Theorem
4.2.1
Consider the circuit in Figure 4.1. Find its Norton’s equivalent circuit.
Draw and label your circuit in Figure 4.4.
4.2.2
Connect the circuit in Figure 4.1. Replace RL with ammeter (multimeter)
and make sure the polarity of ammeter is right. Turn on DC power
supply and record the current. This is the value of Norton equivalent
circuit current source, isc.
4.2.3
Calculate voltage drop across RL from equivalent circuit using formula
below:
VRL=iscRThRL
(3)
RTh+RL
4.2.4
Connect RL to the circuit and remove ammeter. Turn on power supply,
measure and record the voltage drop across RL (a-b terminal).
Compare calculated VRL with measured one.
4.2.5
Repeat step 2 to 4 for circuit in Figure 4.2.
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Name
:
______________________________ Date : ______________
Matrix No
:
______________________________
5.
RESULT:
EXPERIMENT 4: Thevenin’s and Norton’s Theorem
Figure
4.5
Table
4.1
Table
4.2
Figure
4.2
Table
4.3
Table
4.4
Problem
1
Problem
2
MARKS
4
8
8
4
6
6
6
6
48
5.1 Thevenin’s Theorem
For circuit in Figure 4.1
Figure 4.5 : Thevenin equivalent circuit for circuit in Figure 4.1
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%
Name
:
______________________________ Date : ______________
Matrix No
:
______________________________
Table 4.1:
Measured and Calculated Value for circuit in Figure 4.1
Parameter
Measured Value
Calculated Value
Voc
RTh
VRL
For circuit in Figure 4.2
Table 4.2:
Parameter
Measured and Calculated Value for circuit in Figure 4.2
Measured Value
Voc
RTh
VRL
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Calculated Value
Name
:
______________________________ Date : ______________
Matrix No
:
______________________________
5.2 Norton’s Theorem
For circuit in Figure 4.1
Figure 4.2:
Table 4.3:
Parameter
Norton equivalent circuit for circuit in Figure 4.1
Measured and Calculated Value for circuit in Figure 4.1
Measured Value
iSC
VRL
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Calculated Value
Name
:
______________________________ Date : ______________
Matrix No
:
______________________________
For circuit in figure 4.2
Table 4.4:
Parameter
Measured and Calculated Value for circuit in Figure 4.2
Measured Value
iSC
VRL
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Calculated Value
Name
:
______________________________ Date : ______________
Matrix No
:
______________________________
6. EXERCISE:
6.1 Determine the value of Rth, Voc at a-b terminal and i for circuit in Figure 4.6.
Figure 4.6
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Name
:
______________________________ Date : ______________
Matrix No
:
______________________________
6.2 The Thevenin equivalent resistance RTH for the network in figure 4.7 was 3.2
kΩ. Detail how this could be altered to 2 kΩ by using a single resistor placed
across terminal A and B. Calculate the value of the resistor that will accomplish
this. Will the Thevenin voltage change?
Figure 4.7
Value of resistor:________________Ω
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Name
:
______________________________
Matrix No
:
______________________________
7. DISCUSSION:
The Thevenin and Norton Theorem is…
8. CONCLUSION:
The conclusion for this lab is…
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Date: ______________