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Diodes

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p-type n-typeA/ /k

pn

.

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Function Electrical gate

Current only flowsoneway Forward biased

Current flows

Reverse biased

Bloc s current

+ -

- +

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pn construction Semiconductor material n-type

Excesselectrons p-type Excess holes

Join together

De

ple

tio

n re

gio

n Redistribution of charge carriers Contact potential

0.7V

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p-type material

n-type material

Holes diffuseinto the n-type andswallowelectrons

Electrons diffuseinto the

p-type

and

fill h

oles

Depletion region formed

No free charge carriers

0.7V contact potential

pn construction

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Forward bias

Depletion region narrows as appliedvoltageapproaches 0.7V

Appliedvoltage above 0.7V

depletion region is removed charge carriers can flow

V< 0.7V V> 0.7V

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Reverse bias

Depletion region extends

Higher voltage

Brea down

Current flow

V< 0V V

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Using brea down

During fabrication

Brea down voltagedetermined

Specific brea down voltage

Structuredesigned to tolerate reversecurrent

Providesstablevoltage reference

ZENERDiode

Reverse bias connection

- +

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TheZener circuit:

Voltag

eregulat

or

Always Vin > Vout Diode brea sdown

Constant Vout voltage

Set by theZener e.g. 5.1V R limitsmaximum available

current Vout

VinR

max

I

VVR outin

!

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Powe

rdissi

pation

Current always flows through theZener Maintains brea down voltage Power will bedissipated

Heating effect Power rating consideration

)( zeneroutzener IP v"

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LED

Light Emitting Diode

Givesout light ascurrent flows ~ 20mA

After switch on 0.7V

I-V characteristic

Semiconductor material

Different materials

Different coloursoflight

Protection resistor

pn j

ncti

n

i

I-

cha rac t

ri

tics

-

-

-

-

-

-

-

-

Appli

ltage

Current

+ -

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Protection resistor

VLED @ 1.2V Ityp @ 20mA

Vin @ 5V

;!

v

!

!

190

1020

2.153

R

R

I

VVR

typ

LEDin VLED

VinR

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Photodiode

pn junction diode Detects light

photo

Operation

Reverse biasedindar

current at 1nA

Incident light on

junction EHP generation

Large current

FAST reaction times

- +