BEKG1113 PRINCIPLE OF ELECTRICAL AND ELECTRONICS CHAPTER 2 (WEEK 3) FACULTY OF ELECTRONIC AND COMPUTER ENGINEERING

2 Chapter 2 The topics for this chapter: –Voltage and current sources –Resistor –Resistor Color code –Ohm’s Law –Types of circuit - series, parallel and series- parallel circuit –Circuit ground, KVL, KCL, Power dissipation

3 Voltage source –Ideal voltage source Can provide a constant voltage for any current required by a circuit [1]. –Voltage source can either be AC (Alternating current) or DC (Direct current) [2].

4 Voltage source The symbols for voltage sources are represented here [1]: VI characteristics for an ideal voltage source is shown by the graph [1]

5 Voltage source Six categories of voltage sources [1]: –Batteries –Solar cells –Generator –The electronic power supply –Thermocouples –Piezoelectric sonsors

6 Thermocouples –It is a thermoelectric type of voltage source that is commonly used to sense temperature. The operation is based on Seebeck effect. –The types of thermocouples are categorized by letters (J,K,E,N, B and R) that depends on the range of temperature.

7 The graph of thermocouple characteristics. Note that K is the most common thermocouple used.

8 A few types of thermocouples which depend on their specification requirements.

9 Piezoelectric sensors –They act as voltage sources and are based on the piezoelectric effect where a voltage is generated when a piezoelectric material is mechanically deformed by an external force. –Types of piezoelectric material; quartz & ceramic –Applications: pressure sensor, force sensor

Chapter 2: Direct Current (DC) 10 Chapter 2: Direct Current (DC) Circuit The current source –Definition: The ideal current source can provide a constant voltage for any load. –The symbol for a current source is shown below

11 Current Source Constant current sources – a type of power supply

12 Current Source Constant current sources from most transistor circuits Constant current battery chargers

Basic DC Circuit It consists of a source of electrical energy, some sort of load to make use of that energy, and electrical conductors connecting the source and the load. 13 SOURCELOAD + -

Electrical Circuit Requirements Control Device: Allows the user control to turn the circuit on or off. Switches are the devices commonly used for controlling the oppening or closing of circuits. Protection Device: Current must be monitored and not allowed to exceed a safe level as to protect users from shock, to protect the equipment from damage, and to prevent fire hazards. 14

Protective Devices Fuses: Fuses use a metallic element that melts when current exceeds a preset value. It will blow if more current passes through it. Circuit breaker: Circuit breaker works on the different principle. When the current exceeds the rated value of breaker, the magnetic field produced by excessive current operates a mechanism that trips open a switch. After the fault or overload condition has been cleared, the breaker can reset and used again. 15

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Current Direction 17

Circuit Ground Grounding is achieved in an electrical system when one of the conductive wires serving as part of the circuit path is intentionally given a direct path to the earth. This method of grounding is called earth ground. In most electronic equipment, a large conductive area on printed circuit board or the metal housing is used as the circuit ground or chassis ground. 18

Ground is the reference point in electric circuits and has a potential of 0 V with respect to other points in the circuit. All of the ground points in a circuit are electrically the same and therefore common points. 19

20 Resistors Definition: –A component that is specifically designed to have a certain amount of resistance is called resistor.

21 Resistors Fixed resistors: provides a specific constant value of resistance –Carbon-composition –Chip resistor –Film resistor –Wirewound resistor Variable resistor: values can be changed easily with manual or an automatic adjustment –Potentiometer –Rheostat

Carbon-composition Mixture of finely ground carbon, insulating filler and resin binder. The ratio of carbon to insulating filler sets the resistance value. Commonly use fixed resistor. 22

23 Chip Resistors SMT (Surface Mount Technology) component Very small in size,suitable for compact assemblies.

24 Film Resistors The resistive material could be carbon film or metal film. The desired resistance value is obtained by removing part of resistive material in a spiral pattern along the rod

25 Another type of film type resistor

26 Wirewound Resistors Constructed with resistive wire wound around an insulating rod and then sealed. Used in application that require higher power rating resistance

27 Several types of wirewound resistors

Potentiometer used to divide voltage Has 3 terminal; terminal 1&2 have a fixed resistance between them, which is the total resistance. Terminal 3 is connected to moving contact. 28

Rheostat Used to control current Potentiometer can be used as a rheostat by connecting terminal 3 to either terminal 1 or terminal 2 Chapter 2: Direct Current (DC) 29

30 Resistors Resistor color code

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32 Ohm’s Law Ohm’s law states that current is directly proportional to voltage and inversely proportional to resistance. The formula given are: V = IR where: I = current in amperes (A) V = voltage in volts (V) R = resistance in ohms (Ω)

Voltage - is not affected by either current or resistance. It is either too low, normal, or too high. If it is too low, current will be low. If it is normal, current will be high if resistance is low, or current will be low if resistance is high. If voltage is too high, current will be high. Current - is affected by either voltage or resistance. If the voltage is high or the resistance is low, current will be high. If the voltage is low or the resistance is high, current will be low. Resistance - is not affected by either voltage or current. It is either too low, okay, or too high. If resistance is too low, current will be high at any voltage. If resistance is too high, current will be low if the voltage is fix. 33

34 The linear relationship of current and voltage. The relationship can be portrayed by the graph below:

35 Example 1 Show that if the voltage in the circuit is increased to three times its present value, the current will triple in value. R 10V 4.7kΩ

36 Example 2 Assume that you are measuring the current in a circuit that is operating with 25V. The ammeter reads 50mA. Later, you notice that the current has dropped to 40mA. Assuming that the resistance did not change, you must conclude that the voltage source has changed. How much has the voltage changed, and what is its new value?

37 The inverse relationship of current and resistance. As you have seen, current varies inversely with resistance as expressed by Ohm’s law, I = V/R. When the resistance is reduced, the current goes up; when the resistance is increased, the current goes down. For example, if the source voltage is held constant and the resistance is halved, the current doubles in value; when the resistance is doubled, the current is reduced by half.

Chapter 2: Direct Current (DC) Circuit 38 The Inversely Proportional Relationship The inversely proportional can be explained by this graph

39 Example 3 How many amperes of current are in the circuit of figure below? R 100V 22Ω If the resistance in above figure is changed to 47 Ω and the voltage to 50 V, what is the new value of current?

40 Example 4 Calculate the current in figure below. R 50V 1.0kΩ

41 Example 5 –How many milliamperes are in the circuit below? R 30V 5.6kΩ

42 Example 6 –In the circuit below, how much voltage is needed to produce 5 A of current? R V 100Ω 5 A

43 Example 7 –How much voltage will be measured across the resistor below? V V 5 mA R 56Ω

44 Example 8 –Suppose that there is a current of 8 µA through a 10 Ω resistor. How much voltage is across the resistor?

45 Example 9 –In the circuit of figure below, how much resistance is needed to draw 3.08 A of current from battery? 12 V R 3.08 A

46 Example 10 –Suppose that the ammeter in figure below indicates 4.55 mA of current and the voltmeter across the supply reads 150V. What is the value of R?

47 Types of Circuit Series Parallel Series-parallel circuit

48 Series Circuit Resistor in series A series circuit provides only one path for current between two points so that the current is the same through each series resistor [1]. A B

49 The equation of a series resistors circuit The current flow is the same through each element of the series circuit. The voltage across the source or power supply is equal to the sum of the voltage drops across the separate resistors in series.

50 Power Distribution Power distribution in series circuit –It is represented by this equation [2]: –The power delivered by the supply can be determined using the equation [2]:

51 Voltage sources in series [2]: Voltage Sources

52 Example 11 In figures below, find out the total resistance between point A and point B RTRT

53 RTRT RTRT RTRT

54 Voltage Divider The voltage across a resistor in a series circuit is equal to the value of that resistor times the total applied voltage divided by the total resistance of the series configuration [2].

55 Example 12 a.Find the total resistance R T. b.Calculate the resulting source current I s. c.Determine the voltage across each resistor. IsIs 22 55 11

56 Example 13

57 Example 13 a.Determine the total resistance R T. b.Calculate the source current I S. c.Determine the voltage across each resistor. d.Find the power supplied by the battery. e.Determine the power dissipated by each resistor. f.Comment on whether the total power supplied equals the total power dissipated.

58 Parallel Circuit The parallel resistors circuit

59 The equation of a parallel resistors circuit Voltage across each resistor is the same as the voltage across the parallel combination. The current flowing through the parallel combination is the sum of the current in the separate branches.

Power in Parallel Circuits Total power in a parallel circuit is found by adding up the powers of all the individual resistors, the same as for the series circuits. BENG 1113: CHAPTER 2 WEEK 5 60

61 Exercise 14 What is the total resistance between point A and point B

Current Divider A parallel circuit acts as a current divider because the current entering the junction of parallel branches “divides” up into several individual branch currents. 62

Series-Parallel 63

KVL KVL is the abbreviation of Kirchoff’s Voltage Law The sum of the voltage drops around a closed loop is equal to the sum of the voltage sources of that loop Total voltage = 0 64

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KCL Kirchoff’s Current Law The current arriving at any junction point in a circuit is equal to the current leaving that junction Current in = current out 66

BENG 1113: CHAPTER 2 WEEK 5 67

68 The Branch Current Method The branch current method is a circuit analysis method using KVL and KCL to find the current in each branch of a circuit by generating simultaneous equation.

69 Example: The Branch Current Method

70 Currents I1, I2 and I3 are assigned to the branches a as shown. Applying KCL at node a Appling KVL at both loops resulting;

71 The following equations can be written Solving all three equations will give us

The Mesh Current Method In the loop current method, you will work with loop current instead of branch current. BENG 1113: CHAPTER 2 WEEK 5 72

73 The Mesh Current Method

74 Appling KVL at both loops resulting; Solving both equations will give us;

The Node Voltage Method Another method of analysis is node voltage method. It is based on finding the voltages at each node in the circuit using KCL. BENG 1113: CHAPTER 2 WEEK 5 75

The Node Voltage Method 76

77 Currents I1, I2 and I3 are assigned to the branches a as shown. Applying KCL at node a Express the currents in terms of circuit voltages using Ohms’s law

Substituting these terms into the current equation yields; BENG 1113: CHAPTER 2 WEEK 5 78

79 Superposition A linear network which contains two or more independent sources can be analyzed to obtain the various voltages and branch currents by allowing the sources to act one at a time, then superposing the results. This principle applies because the linear relationship between current and voltage. Voltage sources are replaced by short circuits; current sources are replaced by open circuits. Superposition can be applied directly to the computation of power.

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82 By applying superposition principle, with the 200V acting alone, the 20A current source is replaced by an open circuit.

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84 When the 20-A source acts alone, the 200V source is replaced by a short circuit. The total current in the 23Ω resistor is

85 Source Transformation Thevenin’s equivalent Norton’s equivalent

86 Example: The Node Voltage Method

87 Assign all currents are going out from node 1 &2. From node 1; From node 2;

88 Example: Mesh Analysis

89 The matrix that we’ll get Solving -ve sign in I 1 represents that the assigned current direction opposed the actual current direction.

90 Solve the same circuit using node voltage method

91 Solution at node 1 At node 2

92 From these The currents can be determined

93 Test 1 Week 7 Scientific notation and engineering notation, Resistor color code Ohm’s Law, KVL and KCL in Mesh or Node Analysis Basic Circuit measurement and measurement equipment

94 References [1] Thomas L.Floyd; Principle of Electric Circuits 8th Ed; Pearson Education; 2007 [2] Robert L.Boylestad; Introductory Circuit Analysis11th Ed; Pearson Education; 2007