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Electronics Principles & Applications Seventh Edition. Charles A. Schuler. Chapter 3 Diodes (student version). McGraw-Hill. © 2008 The McGraw-Hill Companies Inc. All rights reserved. INTRODUCTION. The PN Junction Characteristic Curves of Diodes Diode Lead Identification

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slide1

Electronics

Principles & Applications

Seventh Edition

Charles A. Schuler

Chapter 3

Diodes

(student version)

McGraw-Hill

© 2008 The McGraw-Hill Companies Inc. All rights reserved.

slide2

INTRODUCTION

  • The PN Junction
  • Characteristic Curves of Diodes
  • Diode Lead Identification
  • Diode Types and Applications
slide3

Dear Student:

This presentation is arranged in segments. Each segment

is preceded by a Concept Preview slide and is followed by a

Concept Review slide. When you reach a Concept Review

slide, you can return to the beginning of that segment by

clicking on the Repeat Segment button. This will allow you

to view that segment again, if you want to.

slide4

Concept Preview

  • Diodes have both P-regions and N-regions. The boundaries are called junctions.
  • The P-region is the anode side. The N-region is the cathode side.
  • There are three possible bias conditions: zero, forward, and reverse.
  • Zero bias is accompanied by a depletion region.
  • Forward bias can collapse the depletion region.
  • Reverse bias enhances the depletion region.
  • Bias determines if diodes will be off or on.
slide5

The P-side of a junction diode is doped with acceptor atoms.

The N-side of a junction diode is doped with donor atoms.

junction

P

N

A silicon crystal

Cathode

Anode

Schematic Symbol

slide6

Depletion region

Zero Bias

The electrons near the junction cross

over and fill the holes near the junction.

Having no carriers, the depletion region is an insulator.

slide7

Forward Bias

The carriers move toward the junction

and collapse the depletion region.

The diode is on.

slide8

Reverse Bias

The carriers move away from the junction.

The depletion region is reestablished

and the diode is off.

slide9

Concept Review

  • Diodes have both P-regions and N-regions. The boundaries are called junctions.
  • The P-region is the anode side. The N-region is the cathode side.
  • There are three possible bias conditions: zero, forward, and reverse.
  • Zero bias is accompanied by a depletion region.
  • Forward bias can collapse the depletion region.
  • Reverse bias enhances the depletion region.
  • Bias determines if diodes will be off or on.

Repeat Segment

slide10

Concept Preview

  • The volt-ampere graph for a resistor is a straight line (a resistor is a linear device).
  • The volt-ampere graph for a diode is non-linear.
  • The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region.
  • Excess reverse bias will result in diode breakdown.
  • The cathode end might be marked with a band.
  • Diodes can be tested with an ohmmeter.
slide11

5 ohms

200

175

150

10 ohms

125

100

mA

75

20 ohms

50

25

0

0

0.5

1.0

1.5

Volts

Resistor volt-ampere characteristic curves

slide12

knee

200

175

150

125

100

Forward current in mA

75

50

25

0

0

0.5

1.0

1.5

Forward bias in volts

Silicon diode volt-ampere characteristic curve

slide13

Linearity

  • The volt-ampere characteristic curve for a resistor is a straight line (linear).
  • A diode has a non-linear characteristic curve.
  • The barrier potential produces a knee in the diode curve.
  • The knee voltage is approximately 0.6 to 0.7 volts for silicon diodes.
slide14

200

175

100 oC

150

125

25 oC

100

Forward current in mA

75

-50 oC

50

25

0

0

0.5

1.0

1.5

Forward bias in volts

The effect of temperature

slide15

breakdown

Reverse bias in Volts

400

600

200

0

20

40

Reverse

current

in mA

60

80

100

120

140

Silicon diode reverse bias characteristic curve

slide16

Cathode lead

Anode lead

slide18

0

Cathode lead

V

mA

Anode lead

The diode is reverse biased by the ohmmeter.

slide19

Silicon diode ohmmeter testing

  • Low resistance in both directions: the diode is shorted.
  • High resistance in both directions: the diode is open.
  • Relatively low resistance in the reverse direction: the diode is leaky.
  • The ratio of reverse resistance to forward resistance is > 1000: the diode is good.
slide20

Diode quiz

At zero bias, diodes show a depletion region

which acts as an________.

insulator

The depletion region is collapsed by applying

_________ bias.

forward

The depletion region is made wider by applying

________ bias.

reverse

A forward-biased diode has its anode________

with respect to its cathode.

positive

Diode forward voltage drop decreases as

temperature ________.

increases

slide21

Concept Review

  • The volt-ampere graph for a resistor is a straight line (a resistor is a linear device).
  • The volt-ampere graph for a diode is non-linear.
  • The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region.
  • Excess reverse bias will result in diode breakdown.
  • The cathode end might be marked with a band.
  • Diodes can be tested with an ohmmeter.

Repeat Segment

slide22

Concept Preview

  • Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators.
  • Diode clippers limit signal amplitude.
  • Diode clamps produce a dc signal component.
  • Diodes can be used to suppress inductive kick.
  • Optocouplers combine light emitting diodes and photodiodes.
  • Fiber optic cables carry light signals.
  • Varicap diodes are used to tune electronic circuits.
slide23

Reverse bias in Volts

4

6

2

0

20

40

Reverse

current

in mA

60

80

100

120

140

A zener diode is designed to break down and

conduct backwards at lower voltages.

slide24

V

I

V

Reverse bias in Volts

4

6

2

0

20

40

Reverse

current

in mA

60

80

100

120

140

The voltage across a conducting

zener is relatively constant.

slide25

Load

Unregulated Supply

Using a zener diode as a voltage regulator

The load is in parallel with the zener and will see a

relatively constant voltage as long as the zener is conducting.

slide26

VOUT is not clipped

This circuit is called a clipper or limiter.

When VIN < 1.2 VPP

VIN

VOUT

The diodes do not conduct.

slide27

+ 0.6 V

VOUT is clipped

The diodes conduct.

- 0.6 V

When VIN > 1.2 VPP

VIN

VOUT

slide28

C is charged.

dc

VPP

- 0.6 V

VOUT(dc) =

2

0.6 V

VOUT is clamped.

This circuit is called a clamp or dc restorer.

When VIN > 1.2 VPP

C

VIN

VOUT

slide29

CEMF

The inductive kick

can cause damage.

slide30

CEMF

Transient suppression diodes can be used with inductive loads.

The coil discharges

through the diode and

there is no arc.

slide31

LED

As the electrons cross the junction, they

lose energy in the form of photons.

slide32

VD

IS =

VS - VD

RS

LED circuit

RS

LED

Power

supply

VS

The typical voltage drop for most LEDs is from 1.5 to 2.5 V.

slide33

RS

Power

supply

VS

Photodiode

Photodiodes are reverse biased and

conduct in the presence of light.

slide34

Input

Output

Output

Input

Optocoupler

slide35

Step-index multimode fiber

Input pulse

Output pulse

The combined shorter and longer path lengths

act to stretch the output pulse.

slide36

Step-index multimode fiber

Due to pulse stretching, high speed data transmission is not possible.

Input

Output

slide37

Single mode fiber

A single path means no pulse stretching and

high speed data transmission is possible.

Input

Output

slide38

Tuning diode

L

C

ZERO BIAS

C is maximum and fR is minimum.

slide39

Tuning diode

L

C

REVERSE BIAS

C is less and fR increases.

slide40

Tuning diode

L

C

MAX. REVERSE BIAS

C is minimum and fR is maximum.

slide41

Diode applications quiz

A circuit used to control the amplitude of a

signal is the ________.

clipper

A circuit used to add a dc component to a

signal is the ________.

clamp

A device containing an LED and a photo-

diode is the ________.

optocoupler

A tuning diode shows less capacitance as

reverse bias ________.

increases

The device that is often used to regulate

voltage is the ________ diode.

zener

slide42

Concept Review

  • Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators.
  • Diode clippers limit signal amplitude.
  • Diode clamps produce a dc signal component.
  • Diodes can be used to suppress inductive kick.
  • Optocouplers combine light emitting diodes and photodiodes.
  • Fiber optic cables carry light signals.
  • Varicap diodes are used to tune electronic circuits.

Repeat Segment

slide43

REVIEW

  • The PN Junction
  • Characteristic Curves of Diodes
  • Diode Lead Identification
  • Diode Types and Applications