Electronic principles - Chapter 1 doc

The ideal model can be called the first approximation... This model is called the the second approximation... The ideal model can be called the first approximation... R S This model i

Electronic PRINCIPLES

SIXTH EDITION

Chapter 1

Introduction

Three kinds of formulas

The definition:

The law:

The derivation:

Invented for a new concept

Summarizes a relationship that exists in nature

Obtained by manipulating other formulas using mathematics

C = Q

V {defines what capacitance is}

Q = CV

f = K Q 1 Q 2

d 2

{does not require verification}

{verified by experiment}

R L

10 V

An ideal voltage source maintains a constant output voltage, regardless of the value of R L

The ideal model can be called

the first approximation.

V RL = 10 Volts

R L

10 V

A real voltage source has

a series resistance.

This model is called the

the second approximation.

R S

V RL < 10 Volts

When R L is equal to or greater than 100 times R S , a real

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

R L

1 A

An ideal current source maintains a constant

output current, regardless of the value of R L

The ideal model can be called

the first approximation.

I RL = 1 Ampere

R L

A real current source has

a shunt resistance.

R S

This model is called the

the second approximation.

When R S is equal to or greater than 100 times R L , a real

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

Thevenin’s theorem can be used to replace any linear circuit with an equivalent voltage source called V TH and an equivalent resistance called R TH

72 V

Remove the load.

Calculate or measure V TH across the open terminals.

V TH

Remove the source.

Calculate or measure R TH .

R TH

The input impedance of

a voltmeter should be at least 100 times greater than the Thevenin resistance to

avoid loading error.

When working with actual circuits, please remember this guideline:

DMMs are usually not a problem since they typically have an impedance of 10 MΩ

6 kΩ 4 kΩ

72 V

6 kΩ (R TH )

R L

24 V (V TH )

The original

circuit

The Thevenin

equivalent circuit

Norton’s theorem can be used to replace any linear circuit with an equivalent current source called I N and an equivalent resistance called R N

72 V

Short the load to find I N .

I N

R N is the same as R TH .

R N

6 kΩ 4 kΩ

72 V

The original

circuit

The Norton

equivalent circuit 4 mA (I N ) 6 kΩ (R N ) R L

The Norton

6 kΩ (R TH )

R L

24 V (V TH )

A Thevenin

equivalent circuit

R N = R TH I N = V TH

R TH

• A solder bridge between two lines

effectively shorts them together.

• A cold solder joint is effectively an open

circuit.

• An intermittent trouble is one that

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

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 = 0/0 {indeterminate}

10 Ω 100 kΩ

10 Ω

A troubleshooting example:

Do the two 10 Ω resistors form

Why?

10 Ω 100 kΩ

10 Ω

A troubleshooting example:

What are the expected

voltages in this circuit?

10 Ω 100 kΩ

10 Ω

A troubleshooting example:

What are some causes for

this voltage being too high?

V

10 Ω 100 kΩ

10 Ω

A troubleshooting example:

What are some causes for

this voltage being too low?

V