Chapter 01 Upelek 1

8/19/2019 Chapter 01 Upelek 1

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduct ion or display.

MALVINO & BATES

SEVENTH EDITION

Electronic

PRINCIPLES


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Introduction

Topics Covered in Chapter 1

• Voltage sources

• Current sources

• Thevenin’s Theorem

• Norton’s Theorem

• Troubleshooting


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Ideal voltage sourceMaintains a constant output voltage, regardless of

the value of RL.The ideal model can be called

the first approximation.

RL10 V VRL= 10 Volts

An ideal source has no internal resistance


4/24Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduct ion or display.

Real Voltage SourceHas an internal resistance in series with the source

This model is called the

the second approximation.

RL10 V

RS

VRL< 10 Volts

When RL is equal to or greater than 100 times RS, a real

voltage source is stiff and the first approximation can be used.



Ideal current sourceMaintains a constant output current,

regardless of the value of RL.

The ideal model can be called

the first approximation.

RL1 A IRL= 1 Ampere



Real current sourceHas a large internal resistance in parallel with the source

RL1 A IRL< 1 AmpereRS

This model is called the the second approximation.

When RS is equal to or greater than 100 times RL, a real

current source is stiff and the first approximation can be used.



Thevenin’s Theorem

• Used to replace any linear circuit with anequivalent voltage source called VTH and an

equivalent resistance called RTH



Thevenin’s Theorem

• Used to replace any linear circuit with anequivalent voltage source called VTH and an

equivalent resistance called RTH

Example Original Circuit :



Thevenin’s theorem can be used to replace any

linear circuit with an equivalent voltage source

called VTH and an equivalent resistance called RTH.

6 kΩ 4 k

Ω

RL72 V 3 kΩ

Remove the load.Calculate or measure VTH

across the open terminals.

VTH

Remove the source.Calculate or measure

Thevenin’s resistance (RTH)

RTH



Thevenin’s Voltage



The input impedance of a voltmeter should be at least 100 times

greater than the Thevenin resistance to

avoid meter loading.

Voltmeter Tip

DMMs are usually not a problem since they

typically have an input impedanceof 10 M

Ω

Meter loading errors cause

inaccurate measurements.

Th i E i l t Ci it



6 kΩ

4 kΩ

3 kΩ

RL72 V

6 kΩ

(RTH)

RL24 V (VTH)

Original

circuit

Theveninequivalent circuit

Thevenin Equivalent Circuit



Norton’s Theorem

Used to replace any linear circuit with an equivalentcurrent source called IN and an equivalent resistance

called RN


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Norton’s Resistance

Short the load to find IN.RN is the same as RTH.

6 kΩ 4 k

Ω

3 kΩ RL72 V INRN

Example Original Circuit :


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Norton’s Current

IN = 4 mA

RN = 6 KΩ

N t E i l t Ci it


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6 kΩ

4 kΩ

3 kΩ

RL72 VThe original

circuit

The Nortonequivalent circuit 6 kΩ (RN)RL4 mA (IN)

Norton Equivalent Circuit


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The Norton

dual 6 kΩ (RN)RL4 mA (IN)

6 kΩ

(RTH)

RL24 V (VTH)A Theveninequivalent circuit

RN

= RTH IN =

VTH

RTHCircuit Conversion


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Solder and Connector Problems

•A solder bridge between two lineseffectively shorts them together.

• A cold solder joint is effectively an open

circuit.

• An intermittent trouble is one that

appears and disappears (could be a coldsolder joint or a loose connection).

T bl h i


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Troubleshooting• Finding out why a circuit is not doing what it is

supposed to do

• Common problems are opens and shorts

• An open device:

– The current through it is zero.

– The voltage across it is unknown.

– V = zero x infinity {indeterminate}

• A shorted device:

– The voltage across it is zero.

– The current through it is unknown.

– I = 0/infinity {indeterminate}


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10Ω 100 k

Ω

10Ω

12 V 100 kΩ

A troubleshooting example:

Do the two 10Ω

resistors form

a stiff voltage divider?

Why?


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10 Ω 100 kΩ

10Ω

12 V 100 kΩ


What are the expected

voltages in this circuit?


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10Ω 100 k

Ω

100 kΩ

V10Ω

12 V


What are some causes for

this voltage (V) being too high?


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10Ω 100 k

Ω

100 kΩ

V10Ω

12 V


What are some causes for

this voltage (V) being too low?

Chapter 01 Upelek 1

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