LABORATORY MODULE ENT 163 Fundamental of Electrical Engineering Semester 1 (2006/2007) EXPERIMENT 4: Thevenin s and Norton s Theorem Name Matrix No. : : School of Mechatronic Engineering Northern Malaysia University College of Engineering
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. PARTS AND EQUIPMENT: 2.1 Breadboard 1 unit 2.2 DC power supply 1 unit 2.3 Digital Multimeter 1 unit 2.4 Wires 2.5 Resistor : 2.5.1 100 Ω resistor - 1 piece 2.5.2 470 Ω resistor - 1 piece 2.5.3 1.0 kω resistor - 1 piece 2.5.4 1.5 kω resistor - 1 piece 2.5.5 4.7 kω resistor - 1 piece 2.5.6 9.1 kω resistor - 1 piece 3. 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 Page 1 of 11
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, i sc and the Thevenin equivalent resistance, R Th. In the Thevenin equivalent circuit, the value of the voltage source is Voc and the value of the series resistor is R Th. In the Norton equivalent, the value of the current source is i sc and the value of the parallel resistor is R Th but it is not necessary to calculate all three quantities, since they are related by following equation: V oc = R Th i sc (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 R Th. When a circuit also contains dependent sources we will modify the method and determine voc and R Th. Page 2 of 11
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 4.3. 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 v s. Once you have built the circuit, set the value of v s 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. Figure 4.1: Schematic diagram of circuits. 4.1.3 Measure and record the voltage across a-b terminal. This is Thevenin equivalent circuit voltage, voc. 4.1.4 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, R Th. 4.1.5 Calculate the voltage drop across RL using this formula below: V RL = v oc R L (2) R Th + R l 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. Page 3 of 11
Figure 4.2: Schematic diagram of circuits. 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: V RL = i sc R Th R L (3) R Th + R L 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. Page 4 of 11
Name : Date: Matrix No : 5. RESULT: 5.1 Thevenin s Theorem For circuit in Figure 4.1: Figure 4.3: Thevenin equivalent circuit for circuit in Figure 4.1 Page 5 of 11
Name : Matrix No: Date : Table 4.1: Measured and Calculated Value for circuit in Figure 4.1 Parameter Measured Value Calculated Value Voc R Th V RL For circuit in Figure 4.2: Table 4.2: Measured and Calculated Value for circuit in Figure 4.2 Parameter Measured Value Calculated Value Voc R Th V RL Page 6 of 11
Name : Matrix No: Date : 5.2 Norton s Theorem For circuit in Figure 4.1: Figure 4.4: Norton equivalent circuit for circuit in Figure 4.1 Page 7 of 11
Name : Matrix No: Date : Table 4.3: Measured and Calculated Value for circuit in Figure 4.1 Parameter Measured Value Calculated Value i SC V RL For circuit in figure 4.2: Table 4.4: Measured and Calculated Value for circuit in Figure 4.2 Parameter Measured Value Calculated Value i SC V RL Page 8 of 11
Name : Matrix No: Date : 6. EXERCISE: 6.1 Determine the value of R th, Voc at a-b terminal and i for circuit in Figure 6.1. Figure 6.1 Page 9 of 11
Name : Matrix No: Date : 6.2 The Thevenin equivalent resistance RTH for the network in figure 6.2 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 6.2 Page 10 of 11
Name : Date : Matrix No: 7. DISCUSSION: 8. CONCLUSION: Page 11 of 11