1.1.2b PostInvestigating Basic Circuits.pptx

Investigating Basic Circuits

Post-Activity Discussion

© 2014 Project Lead The Way, Inc. Digital Electronics

Answers the following questions:

• _{What are some of the basic components that make up}

simple circuits and what do they do?

• _{What are the important characteristics of a circuit and}

how do I measure different parts of a circuit?

• _{How do I work safely with circuits?}

• _{How do I measure voltage in a circuit?}

• _{How does the arrangement of components affect the}

characteristics of the circuit?

• _{How can I use calculations to design circuits before I}

start creating one?

This Presentation Will…

Light Emitting Diode (LED)

3

• In Activity 1.1.2 Investigating Basic Circuits you created a simple circuit similar to the one shown below.

• With the circuit active, what happened when you flipped the LED in the opposite direction?

The LED will not light up.

• What does that tell you about LEDs (a type of diode)?

Resistors

4

• What do you think the role of the resistor is in the circuit?

The resistor protects the LED by limiting the flow of current through it.

Resistor - Component made of material that

opposes flow of current and therefore has some

value of resistance.

How to Properly Use a DMM

• What happened when you switched the leads?

• Everyone read slightly different values. Why?

5

5 V - 5 V

The DMM still reads the voltage, it is just negative. Tolerances of components.

How to Properly Use a DMM

• How do you ensure the best precision in reading voltage with the DMM? (most significant figures)

The DMM reading becomes more precise by a factor of ten each time the voltage range is decreased.

6

Range Reading

600V-0V 005V (1 s.f.) 20V-0V 4.7V (2 s.f.) 2V-0V 1 or +Over

• Why was there no reading at 2V-0V?

The range is too small.

What is Voltage?

7

• Now that you can measure it, let’s explore what voltage is in more detail.

• Voltage is the electrical force that causes current to flow in a circuit. It is measured in VOLTS.

• This force can be created by separating charges.

• Voltage has been described many different ways as the science around electricity has evolved.

• We will describe voltage by looking at another common component in electronics called a capacitor.

Capacitors

• _{A capacitor is an electronic component that can be used}

to store an electrical charge.

• _{A capacitor can be thought of as a temporary battery.}

8

+ + + + + + + + + +

What is Voltage?

9

Example:

Parallel Plate Capacitor

• A battery pushes charge onto opposite plates which

generates an electric field. • Theoretically, a positive test

charge placed in the field has the potential to move.

• Can you guess which way the test charge would move in this electric field? + + + + + + + + + + -+ Test Charge

Good guess! The test charge has the potential to move left. (opposites attract)

What is Voltage?

10

Example

Parallel Plate Capacitor

• If a conductor were to touch

both plates, all the charges one would move to the other.

• This can create a lot of current! • Be careful when dealing with

high voltage capacitors.

+ + + + + + + + + +

Voltage Source: Battery

• _{A battery is a device that converts chemical energy into}

electrical energy.

• _{The chemical reaction provides more charges for a longer}

time than a capacitor does.

• _{One side of a battery has the potential to do work}

(12V) High Potential (right side of battery)

• _{One side of a battery has no potential to do work}

(0V) Low Potential or Ground (left side of battery)

• _{The battery would make both test charges move to the right.}

- + +

Test Charge A

+

What is Voltage?

In order for a charge to move, there must be a separation of charge or a potential difference across two points in the circuit.

Voltage is defined mathematically as ΔV = V _final – V _initial

A Volt(V) is a Joule(J) of work per Coulomb (C) of charge. 1V = 1J

1C

A 12V battery is able to do 12 Joules of work for every 1 Coulomb of charge the battery can provide. 12

What is Voltage?

Both of these situations read zero volts on the DMM. Why?

(6a) (6b)

There is no separation of charge. For each of these arrangements, the

potential difference or voltage across the test points is zero. (6a) ΔV = 5V-5V=0

Current: An Analogy

14

Force

The flow of water from one tank to another is a good analogy for an electrical circuit and the mathematical relationship between voltage, resistance, and current.

Force: The difference in the water levels ≡ Voltage

Flow: The flow of the water between the tanks ≡ Current

Opposition: The valve that limits the amount of water ≡ Resistance

Flow

- +

Anatomy of a Flashlight

15

D - Cell

D - Cell

Switch _Switch

Light

Bulb Light_Bulb

Battery

Battery

Flashlight Schematic

• _{Closed circuit (switch closed)} • _{Current flow}

• _{Lamp is on}

• _{Lamp is resistance, uses}

energy to produce light (and heat)

• _{Open circuit (switch open)} • _{No current flow}

• _{Lamp is off}

• _{Lamp is resistance, but is not}

using any energy

16

- + - +

Current

Voltage

Current Flow

• _{Conventional Current assumes}

that current flows out of the positive side of the battery,

through the circuit, and back to the negative side of the battery. This was the convention

established when electricity was first discovered, but it is incorrect!

• _{Electron Flow is what actually}

happens. The electrons flow out of the negative side of the battery, through the circuit, and back to the positive side of the battery.

17

Electron Flow

Conventional Current

Engineering vs. Science

• _{The direction that the current flows does not affect what the}

current is doing; thus, it doesn’t make any difference which convention is used as long as you are consistent.

• _{Both Conventional Current and Electron Flow are used. In}

general, the science disciplines use Electron Flow, whereas the engineering disciplines use Conventional Current.

• _{Since this is an engineering course, we will use} Conventional Current.

18

Electron Flow

Conventional Current

Ohm’s Law

• _{Defines the relationship between voltage, current, and}

resistance in an electric circuit

• _{Ohm’s Law:}

Current in a resistor varies in direct proportion to the voltage applied to it and is inversely proportional to the resistor’s value.

• _{Stated mathematically:}

Where: I is the current (amperes)

V is the potential difference (volts) R is the resistance (ohms)

V

I R

+

-19

R V

Ohm’s Law Triangle

V

I R

V

I R

V

I R

20

) A , amperes (

R

V I 

) , ohms (

I V

R  

) V , volts (

R I V 

Example: Ohm’s Law

Example:

The flashlight shown uses a 6 volt battery and has a bulb with a resistance of 150 . When the flashlight is on, how much current will be drawn from the battery?

21

V_T = +

-V_R I_R

Example: Ohm’s Law

Example:

The flashlight shown uses a 6 volt battery and has a bulb with a resistance of 150 . When the flashlight is on, how much current will be drawn from the battery?

Solution:

22

V_T = +

-V_R I_R

Schematic Diagram

V

I R

mA 40 A

0.04 150

6 R

V I R

R   _  

Circuit Configuration

23

What happened when you removed an LED from each of these circuits?

Circuit Configuration

Series Circuits

• _{Components are connected}

end-to-end.

• _{There is only a single path for}

current to flow.

Parallel Circuits

• _{Both ends of the components are}

connected together.

• _{There are multiple paths for}

current to flow.

24

Components

(i.e., resistors, batteries, capacitors, etc.)

Components in a circuit can be connected in one

of two ways.

Kirchoff’s Voltage Law (KVL)

25

• In this circuit we used a 5V power source.

• The resistor you measured had roughly 3V across it.

• What did you guess would be the voltage across the LED?

V

=V

+ V

5V = 3V + 2V

Power Source (a)Voltage across LED and Resistor (b) Voltage across Resistor only 5V 5V 3V

Series Circuits

Characteristics of a series circuit

• _{The current flowing through every series component is equal.}

• The total resistance (R_T) is equal to the sum of all of the resistances

(i.e., R₁ + R₂ + R₃).

• The sum of all of the voltage drops (V_R1 + V_R2 + V_R2) is equal to the

total applied voltage (V_T). This is called Kirchhoff’s Voltage Law.

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V_T +

-V_R2 + -V_R1

+

-V_R3 +

-R_T I_T

Example: Series Circuit

Example:

For the series circuit shown, use the laws of circuit theory to calculate the following:

• The total resistance (R_T)

• The current flowing through each component (I_T, I_R1, I_R2, and I_R3) • The voltage across each component (V_T, V_R1, V_R2, and V_R3)

• Use the results to verify Kirchhoff’s Voltage Law.

27

V_T +

-V_R2 + -V_R1

+

-V_R3 +

-R_T I_T

I_R1 I_R3

Example: Series Circuit

Current Through Each Component:

             k 1.89 1890 R k 1.2 470 220 R R3 R2 R1 R T T T mAmp 6.349 I I I I : circuit series a is this Since mAmp 6.349 k 1.89 v 12 I Law) s (Ohm' R V I R3 R2 R1 T T T T T        

Example: Series Circuit

Solution:

29

Voltage Across Each Component:

V I R volts 7.619 Ω K 1.2 mA 6.349 V Law) s (Ohm' R3 I V volts 2.984 Ω 470 mA 6.349 V Law) s (Ohm' R2 I V volts 1.397 Ω 220 mA 6.349 V Law) s (Ohm' R1 I V R3 R3 R3 R2 R2 R2 R1 R1 R1                

Example: Series Circuit

Solution:

30

Verify Kirchhoff’s Voltage Law:

v 12 v

12

v 619 . 7 v 984 . 2 v 397 . 1 v 12

V V

V

V_{T R1 R2 R3} 

 



 

Kirchoff’s Current Law (KCL)

31

Note:

• LEDs can be viewed as resistors in this circuit to simplify the discussion.

• The 330Ω resistor was also removed to make the relationship easier to see. • Why do you think the 330Ω resistor

placed in the actual circuit when the components are arranged this way?

• For components that are in series, the current is the same in each component regardless of the

resistance values.

• In this circuit configuration, if R1 and R2 have different resistances the current is not the same. • What would R1 and R2 have in common? Voltage

Parallel Circuits

Characteristics of a Parallel Circuit

• _{The voltage across every parallel component is equal.}

• The total resistance (R_T) is equal to the reciprocal of the sum of the

reciprocal:

• The sum of all of the currents in each branch (I_R1 + I_R2 + I_R3) is equal

to the total current (I_T). This is called Kirchhoff’s Current Law.

32 + -+ -V_R1 +

-V_R2 V_R3

R_T V_T I_T + -3 2 1 T 3 2 1 T R 1 R 1 R 1 1 R R 1 R 1 R 1 R 1      

Example: Parallel Circuit

Example:

For the parallel circuit shown, use the laws of circuit theory to calculate the following:

• The total resistance (R_T)

• The voltage across each component (V_T, V_R1, V_R2, and V_R3)

• The current flowing through each component (I_T, I_R1, I_R2, and I_R3) • Use the results to verify Kirchhoff’s Current Law.

33 33

+

-+ -V_R1

+

-V_R2 V_R3

R_T V_T

I_T

+

Example: Parallel Circuit

Solution:

34

Total Resistance:

Voltage Across Each Component:

volts 15 V V V V : circuit parallel a is this Since R3 R2 R1

T                59 . 346 R k 3.3 1 k 2.2 1 470 1 1 R R 1 R 1 R 1 1 R T T 3 2 1 T

Example: Parallel Circuit

Solution:

35

V

I R

Current Through Each Component:

mAmp 43.278 346.59 v 15 R V I mAmp 545 . 4 k 3.3 v 15 R3 V I mAmps 6.818 k 2.2 v 15 R2 V I mAmps 31.915 470 v 15 R1 V I Law) s (Ohm' R1 V I T T T R3 R3 R2 R2 R1 R1 R1 R1                 

Example: Parallel Circuit

Solution:

36

Verify Kirchhoff’s Current Law:

mAmps 43.278

mAmps 43.278

mA 545 . 4 mA 818 . 6 mA 31.915 mAmps

43.278

I I

I

I_{T R1 R2 R3} 

 

 

 

Summary of Kirchhoff’s Laws

37

Kirchhoff’s Voltage Law (KVL):

The sum of all of the voltage drops in a series circuit equals the total applied voltage.

Gustav Kirchhoff 1824-1887 German Physicist

Kirchhoff’s Current Law (KCL):

The total current in a parallel circuit equals the sum of the individual branch currents.

Up Next

38

Now that you have been introduced to some of the basic characteristics, components, and measurement tools used in electronics, we will build on that knowledge in the

upcoming activities.

• _{Scientific & Engineering Notation}

• _{Component Identification: Analog Devices} • _{Circuit Theory Laws}

Hand Calculations Simulation

Analog Versus Digital

39

• _{The circuits we have explored to this point have included}

only analog components.

• _{Later we will be learning what some of the digital}

components are and how they can be used to create desired outputs to a circuit given specific inputs.

The Random Number Generator

40

• _{The Random Number Generator (RNG) is an example}

circuit that we will use to illustrate all the parts of a complete circuit design.

• _{It includes an analog section and two digital sections.}

Push Button

0 0 0 1 1 1

0 1 1 0 0 1

1 0 1 0 1 0

1 2 3 4 5 6

Analog Section

Sequential Logic Section (Digital)

Combinational Logic Section (Digital)

Random Number Output Push

Button Imput