ElectronicsOverviewOverview: the Property of One-: the Property of One-way Conduction of diodesway Conduction of diodes

1. forward bias1. forward bias （（ P is positive and N is nagativP is positive and N is nagativee ）） the current flow is significantthe current flow is significant

2. reverse bias2. reverse bias （ （ P is nagativeP is nagative and N is positiveand N is positive ） ） the current flow is very smallthe current flow is very small

3. No any one-way conduction when diodes 3. No any one-way conduction when diodes work beyond Uwork beyond U BK BK

4. Reverse current flow will be influnced by te4. Reverse current flow will be influnced by temperature.mperature.5.The property of saturation of reverse curren5.The property of saturation of reverse current flow.t flow.

ElectronicsChapter6 Sources of Stable DC Voltage(Page 167)

1. Diode Rectifiers

2. Power Supply Filtering

3. Voltage Regulator

Electronics

Sources of Stable DC Voltage

The small power supplyThe small power supply

u4 uou3u2

u1

ACAC

LoadLoad

TransformerTransformer RectifierRectifier FilterFilter RegulatorRegulator

DCDC

Electronics1. Diode Rectifiers

• Half-Wave Rectifier

• Full-Wave Bridge Rectifier

ElectronicsHalf-Wave Rectifier

–

+ +

–

aTrD

uou

b

RL

io动画

u

tO

uo

Ot

U2

U2

?To calculate the average value of output voltage

U0.45oU

Electronics

Full-Wave Bridge Rectifier

－

t

RLu

io

uo

1

23

4a

b

+

–

+

–

－

动画

uo

u

t

U2

U2

Positive half cycle,D1\D3 conduct,D2\D4 are reverse biased

?To calculate the average value of output voltage UUo 0.9

ElectronicsFull-Wave Bridge Rectifier D1

RL uo

D6

D3 D5

D4D2

io

Cb

au

++

–

–

o

Common cathode

Common anode

Electronics

From time From time tt11~~tt22 : :

uuoo==uuabab

D1

RL uo

D6

D3 D5

D4D2

io

Cb

au

++

–

–

o

Output voltage

u:The transformer secondary voltage 动画

u

o

ub uCua

2 t

uo

ott1 t2 t3 t4 t5 t6 t7 t8 t9

Electronics

t1 t2 t3 t4 t5 t6 t7 t8 t9

uo

to

D1

RL uo

D6

D3 D5

D4D2

io

cb

au

++

–

–

o

负载电压

u

o

ua ub uC

2 t

UUo 2.34

ElectronicsHomework

• To calculate the average value of output voltage in half and full-wave rectifier circuits.

• To calculate the average value of current of every diode in half and full-wave rectifier circuits

• To calculate the maximum reverse bias voltage that every diode endures in half and full-wave rectifier circuits

Electronics2.Power Supply Filtering

u RLuo

+ +

– –

~ +C

C: Smoothing Capacitor

Electronics2.Power Supply Filtering

+C

ic

i

–

+ +

–

aD

uou

b

RL

io

= uC

动画

uo

U2

U2

u

tO

tO

25)(3L

TCRτ

((T T — — the period of voltage)the period of voltage)

Electronics

iD

t

uo

U2

tO

O

IIpeakpeak

To choose diodes:To choose diodes: IIOM OM =2 =2 IID D

RLC is larger the peak valure of iD is larger

Electronics3. Voltage Regulator

• Zener Diode Shunt Regulator

• Voltage Regulator

ElectronicsZener Diode Shunt Regulator

U

IUZ

+

–UI RL

+C

IO

UO

+

–

+

–u

IR R

DZ

Iz

Stable voltagecircuit

ElectronicsZener Diode(Page 11)

• UZ(2CW13:5~6.5V)

• Voltage stable constant

(Page 12)

Figure 1.3.2

U

IUZ

ElectronicsZener Diode Shunt Regulator(Page 176)

UO = UZ

UO +UR= UI

IR = IO + IZ

U

IUZ

RL(IO) IR

to assume RL is changed

UO IR (IRR) UO (UZ ) IZ

+

–UI RL

+C

IO

UO

+

–

+

–u

IR R

DZ

Iz

Stable voltagecircuit

Electronics

Ui

T

R2UZ

RL UO

+

–R3+

+

––

+

UB

+

–DZ

+

–Uf

+

–

R11R

1R

Zener Diode Shunt Regulator(Page 177)

there are four parts.

regularamplifie

r

reference sample

Electronics

Z21

1

BO

)(1 URR

RUU

output

Ui

T

R2UZ

RL UO

+

–R3+

+

––

+

UB

+

–DZ

+

–Uf

+

–

R11R

1R

ElectronicsIC Voltage Regulator

Three points

The constant voltage output

Flexible voltage Flexible voltage outputoutput

Positive output78XX

negative output79XX

（ 1. 25 ~ 37 V ）

Electronics

Introduction of pointsIntroduction of points

W7800

1—input3 —common

2 —output

W7900

1 — common3—input

2 —output

Electronics

(1)(1) constant voltage outputconstant voltage output

UUinputinput-U-Uoutout

putputis moris more than 3Ve than 3V

CO

W7805

CiUi

+

_

+

_

UO

1 2

3

0.1~1F 1F

To improve transiet To improve transiet outputoutputTo imorove the waveTo imorove the wave

Electronics

(2)(2)Both positive and negative voltage Both positive and negative voltage outputoutput

23

220V

24V +C

24V+C

W7815

Ci

+15V1 2

3

Ci

W7915

1CO

CO

– 15V

1F

1F

0.33F

0.33F

1000F

1000F

Electronics?

• What is significant as a voltage source?