Topic 1

Basic Concept and Theorem

Electronics PartsBeside resistor, the most common electronics component used in electronics circuits are capacitor and inductor.

Measurement and instrumentations

• Power Supply

• Voltmeter

• Ammeter

• Oscilloscope

• Function generator

The Area of electronics

Electronics

Power Electronics:Switching power supply

Converter Circuits

Electronics: DVD player, IPod,

amplifier

Microelectronics:IC, microprocessor

Electrical:Lighting, fan, a/c

Energy sources DC power source sources Example:

• Battery: Rechargeable and alkaline non rechargeable

• Solar panel

• DC power supply

Energy sources AC sources:

Two standards:American Standard: 110-120 Volts 60HzUK/Malaysia Standard: 220-240 Volts 50Hz

TNB supply

Hydro powernuclear powerwind power

Conductor, insulator and semiconductor

• Resistance of a conductor is very low. It offers very little resistance to charge flow.

• Resistance of insulator is very high. It significantly resists charge flow.

• Resistance of semiconductor is between that of conductor and insulator.

Current (A)Electric current (I) is a flow of electric charge through a medium. This charge is typically carried by moving electrons in a conductor such as wire, measure in ampere.

What is the current of Meter 1 and Meter 2?

Currents• Current is a fundamental variable in electricity and electronics.• It is represented by the symbol I.• Current as a flow of electric

charge.• The current flows from the

positive battery terminal, through the external circuit, and returns to the negative battery terminal.

• The unit of current is ampere (A).• The charge of one electron is

.second 1

coulomb 1ampere 1

Ce 1910602.1

Currents

• There must be a continuous path for the electrons to flow from the negative terminal to the positive terminal of the battery.

• In direct current (dc), the current direction and values are fixed and do not vary with time.

• Current that varies with time is called alternating current (ac).

where I = current in amperes (A),

Q = charge in coulombs (C),

t = time in seconds (s).t

QI

Example

240 C of charge flows through a 200 W light bulb in 2 minutes. Find the current through the bulb.

Solution .2602

240A

s

C

t

QI

Example

A bicycle lamp draws 2 A of current. Find the number of coulombs of charge per second required to create this current. Then find the number of electrons per second required to create this current.

Solution

Number of charge = 2 A 1 s = 2 C.

Number of electrons = .1025.1106.1

2 1919

Voltage (V)Voltage (V) is electric potential between two terminals, measured in volt.

Measuring voltage

Voltage Behaviour• Parallel voltage • Series voltage

Parallel voltage source will have the same voltage like one source but its capacity will multiplies.

Series voltage source will have the same capacity like one source but its voltage will multiplies.

Power (P)Electric power (P) is the rate at which electric energy is transferred by an electric circuit. The SI unit of power is the watt. When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work. Measure as watts.

Resistance

• Electric resistance represented by R.• The unit of electric resistance is ohm ().

where R = resistance in ohms (), = resistivity of electric material in ohm-meter ( m), l = length of material in meter (m), A = cross-sectional area in square meter (m2).• Resistivity is an inherent characteris of the material.

A

lR

Example

Find the resistance of 100 feet of copper wire with a diameter of 50.8 mils.

(Resistivity of copper is 1.7210-8 m.)

Solution r = ½ 50.8 mils = 6.45210-4 m.

l = 100 feet = 30.48 m.

4.0

)10452.6(

48.30)1072.1(

248

m

mm

A

lR

Example

A Teflon shim is used to insulate between two metal plates, forming a capacitor. The Teflon shim is 2 mm thick. The area is 1 cm by 1 cm. What is its resistance?

(Resistivity of Teflon is 31012 m.)

Solution

13

12

106

01.001.0

002.0)103(

mm

mm

A

lR

Example

A cylindrical germanium component has a length of 5 mm and a radius of 2 mm. Find its resistance.

(Resistivity of germanium is 0.47 m.)

Solution

187

)002.0(

005.0)47.0(

2m

mm

A

lR

Resistor ()Resistors determine the flow of current in an electrical circuit. Where there is high resistance in a circuit the flow of current is small, where the resistance is low the flow of current is large. Resistance, voltage and current are connected in an electrical circuit by Ohm’s Law.

Measuring resistor

Band 1, 2, 3 and multiplier (10x)

Colour Digit

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Gray 8

White 9

Resistor colour code

Example The colour code of a carbon composite resistor is

yellow, violet, brown and silver. Find its (a) nominal value and

(b) range of possible values.Solution

(a) Resistance Rnominal = 47101 = 470 .(b) Band 4 silver = 10%. Minimum R = 470 – 0.1 470 = 423

Range of R is 423 through 517

Maximum R = 470 + 0.1 470 = 517

Load (resistor) Behaviour

• Parallel load • Series load

Ohm’s law

• Ohm’s law states that the voltage V across a resistor is directly proportional to the current flowing through the resistor.

• Ohm’s law for resistance

where

R = resistance of the component in ohms( ),

V = voltage across the component measured in volts (V),

I = current through the component measured in amps (A).

IRV

Resistance and Ohms Law

• The resistance R of an element denotes its ability to resist the flow of electric current, it is measured in ohms ().

• A short circuit is a circuit element with resistance approaching zero.

• An open circuit is a circuit element with resistance approaching infinity.

• Conductance is the ability of an element to conduct electric current, it is measured in mhos or Siemens (S).

Nodes, Branches and Loops

Covered under nodal analysis, Kirchhoff’s current and voltage law

Kirchhoff’s current law

• Definition

Kirchhoff’s current Law states that the algebraic sum of currents enterimg a node ( or a closed boundary) is zero.

• The sum of the currents entering a node is equal to the sum of the currents leaving the node.

Kirchhoff’s Current LawKCL: The total current entering a node is equal to total current leaving the node.

43251 IIIII

II outin

Nodal analysis technique• Identify the node

• Use KCL to determine the node current.

Example, for the node to the right KCL yields the equation: Ia + Ib + Ic = 0

• Express the current in each branch in terms of the nodal voltages , V=IR

Example: Nodal Analysis

• Assign a nodal voltage at the node, V1

• Apply KCL to Each NodeI1 + I2 + I3 = 0

Current divider rule Current divider Rule is useful in determining the current flow through one branch of a parallel circuit.

Kirchhoff’s Voltage Law

• Definition

Kirchhoff’s Voltage Law states that the algebraic sum of the potential rises and drops around a closed loop (or path )is zero. i.e. V=0

Kirchhoff’s Voltage LawThe summation of voltage rises and voltage drops around a closed loop is equal to zero.

0321 VVVE

Series CircuitsBased on the Kirchhoff’s law to the closed loop:

)...( 21 nRRRIE

The circuit can be simplify as below:

Voltage divider rule

Potentiometer

The voltage divider is useful in determining the voltage drop across a resistor within a series circuit.

The Voltage Divider RuleThe Voltage Divider Rule is used to determine the voltage drop at each resistors:

ERR

RV

ERR

RV

21

22

21

11

• The circuit here has three resistors, R1, R2, and R3 and two sources of emf, Vemf,1 and Vemf,2

• This circuit cannot be resolved into simple series or parallel structures.

• To analyze this circuit, we need to assign currents flowing through the resistors.

• We can choose the directions of these currents arbitrarily.

Example - Kirchhoff’s Rules

• The circuit here has three resistors, R1, R2, and R3 and two sources of emf, Vemf,1 and Vemf,2

• This circuit cannot be resolved into simple series or parallel structures

• To analyze this circuit, we need to assign currents flowing through the resistors.• We can choose the directions of these currents arbitrarily.

Example - Kirchhoff’s Rules

• At junction b the incoming current must equal the outgoing current

• At junction a we again equate the incoming current and the outgoing current

• But this equation gives us the same information as the previous equation!

• We need more information to determine the three currents – 2 more independent equations

Example - Kirchhoff’s Laws

i2 i1 i3

i1 i3 i2

• To get the other equations we must apply Kirchhoff’s Loop Rule.

• This circuit has three loops.– Left

• R1, R2, Vemf,1

– Right

• R2, R3, Vemf,2

– Outer

• R1, R3, Vemf,1, Vemf,2

Example - Kirchhoff’s Laws

• Going around the left loop counterclockwise starting at point b we get

• Going around the right loop clockwise starting at point b we get

• Going around the outer loopclockwise startingat point b we get

• But this equation gives us no new information!

Example - Kirchhoff’s Laws

i1R1 Vemf ,1 i2R2 0 i1R1 Vemf ,1 i2R2 0

i3R3 Vemf ,2 i2R2 0 i3R3 Vemf ,2 i2R2 0

i3R3 Vemf ,2 Vemf ,1 i1R1 0

• We now have three equations

• And we have three unknowns i1, i2, and i3

• We can solve these three equations in a variety of ways

Example - Kirchhoff’s Laws

i1 i3 i2 i1R1 Vemf ,1 i2R2 0 i3R3 Vemf ,2 i2R2 0

i1 (R2 R3)Vemf ,1 R2Vemf ,2

R1R2 R1R3 R2R3

i2 R3Vemf ,1 R1Vemf ,2

R1R2 R1R3 R2R3

i3 R2Vemf ,1 (R1 R2 )Vemf ,2

R1R2 R1R3 R2R3

Series Circuit A series circuit is one with all the loads in a row.

There is only ONE path for the electricity to flow. If this circuit was a string of light bulbs, and one blew out, the remaining bulbs would turn off.

UNDERSTANDING & CALCULATING SERIES CIRCUITS BASIC RULES

• The same current flows through each part of a series circuit.

• The total resistance of a series circuit is equal to the sum of individual resistances.

• Voltage applied to a series circuit is equal to the sum of the individual voltage drops.

• The voltage drop across a resistor in a series circuit is directly proportional to the size of the resistor.

• If the circuit is broken at any point, no current will flow.

"1. The same current flows through each part

of a series circuit." • In a series circuit, the

amperage at any point in the circuit is the same. This will help in calculating circuit values using Ohm's Law.

• You will notice from the diagram that 1 amp continually flows through the circuit. We will get to the calculations in a moment

"2. The total resistance of a series circuit is

equal to the sum of individual resistances."

• In a series circuit you will need to calculate the total resistance of the circuit in order to figure out the amperage. This is done by adding up the individual values of each component in series. In this example we have three resistors. To calculate the total resistance we use the formula:

RT = R1 + R2 + R3

Calculate the current

• Now with these two rules we can learn how to calculate the amperage of a circuit. Remember from Ohms Law that I = V / R. Now we will modify this slightly and say I = V / R total.

• Lets follow our example figure: • RT = R1 + R2 + R3 • RT = 7 Ohms • I = V / RT • I = 12V / 7 Ohms • I = 1.7 Amp

"Voltage Drops"

• Before we go any further let's define what a "voltage drop" is. A voltage drop is the amount the voltage lowers when crossing a component from the negative side to the positive side in a series circuit. If you placed a multimeter across a resistor, the voltage drop would be the amount of voltage you are reading. This is pictured with the red arrow in the diagram

"Voltage Drops"

• A battery is supplying 12 volts to a circuit of two resistors; each having a value of 5 Ohms. The total resistance.:

RT = R1 + R2 = 5 + 5 = 10 Ohms • The current in the circuit

I = V / RT = 12V / 10 = 1.2 A• The voltage drops across each resistor is using Ohm's Law (V = I x R).

V1 = 1.2A x 5 = 6 V

V2 = 1.2A x 5 = 6V

"4. The voltage drop across a resistor in a series circuit is directly proportional to the

size of the resistor."

• This is what we described in the Voltage Drop section above.

• Voltage drop = Current X Resistor size.

"5. If the circuit is broken/open at any point,

no current will flow."

• The best way to illustrate this is with a string of light bulbs. If one is burnt out, the whole thing stops working.

Parallel Circuits

A parallel circuit is one that has two or more paths for the electricity to flow, the loads are parallel to each other. If the loads in this circuit were light bulbs and one blew out, there is still current flowing to the others because they are still in a direct path from the negative to positive terminals of the battery.

UNDERSTANDING & CALCULATING

PARALLEL CIRCUITS • A Parallel circuit is one with several different paths for the

electricity to travel. • It's like a river that has been divided up into smaller streams,

however, all the streams come back to the same point to form the river once again.

• The total resistance of a Parallel Circuit is NOT equal to the sum of the resistors (like in a series circuit). The total resistance in a parallel circuit is always less than any of the branch resistances. Adding more parallel resistances to the paths causes the total resistance in the circuit to decrease. As you add more and more branches to the circuit the total current will increase because Ohm's Law states that the lower the resistance, the higher the current.

BASIC RULES • A Parallel circuit has certain characteristics and basic

rules: • A parallel circuit has two or more paths for current to flow

through. • Voltage is the same across each component of the parallel

circuit. • The sum of the currents through each path is equal to the

total current that flows from the source. • You can find total resistance in a Parallel circuit with the

following formula:1/RT = 1/R1 + 1/R2 + 1/R3 +...RT is the Total resistance

• If one of the parallel paths is broken, current will continue to flow in all the other paths.

1. "A parallel circuit has two or more paths for current to flow through."

• Simply remember that PARALLEL means two paths up to thousands of paths. The flow of electricity is divided between each according to the resistance along each route.

2. "Voltage is the same across each component of the parallel circuit."

• You may remember from the last section that the voltage drops across a resistor in series. Not so with a parallel circuit. The voltage will be the same anywhere in the circuit.

3. "The sum of the currents through each path is equal to the total current that flows

from the source."

• If one path is drawing 1 amp and the other is drawing 1 amp then the total is 2 amps at the source. If there are 4 branches in this same 2 amp circuit, then one path may draw 1/4A (.25A), the next 1/4A (.25), the next 1/2A (.5A) and the last 1A.

• Don't worry, the next rule will show you how to figure this out. Simply remember for now that the branch currents must be equal to the source current.

4. "You can find TOTAL RESISTANCE in a Parallel circuit with the following

Example

Find the total resistance of the following circuit.

5. "If one of the parallel paths is broken, current will continue to flow in all the other paths."

• The best way to illustrate this is also with a string of light bulbs in parallel. If one is burnt out, the others stay lit.

Series/parallel combination resistors circuitA combination circuit is one that has a "combination" of series and parallel paths for the electricity to flow. Its properties are a combination of the two. In this example, the parallel section of the circuit is like a sub-circuit and actually is part of an over-all series circuit.

Combination Circuit

• The best advice in finding the values for a combination circuit is to first break each part of the circuit down into series and parallel sections and follow those formulas. Once that is complete, combine them for your main calculations.

ExampleDetermine the total combination series-parallel circuit below.

End of part 1a