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Kuliah Elektronika Dasar

Minggu ke 4

DIODA

Jurusan Teknik Elektro

Fakultas Teknik UGM2007

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pn junction diode I-V characteristics

-10

-5

0

5

10

15

20

-6 -5 -4 -3 -2 -1 0 1 2 3 4

Applied voltage

Current

I-V characteristic

Forward Bias

Reverse Bias

Breakdown Voltage

Reverse saturation current 0.7V Switch-on

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PN CONSTRUCTION

Semiconductor material

n-type Excess electrons

p-type Excess holes

Join together

Depletion region Redistribution of charge carriers

Contact potential

0.7V

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p-typematerial

n-typematerial

SAMBUNGAN PN

Holesdiffuse into the n-type andswallow electrons

Electronsdiffuse into the p-type and fillholes

Depletion regionformed No free charge carriers

0.7V contact potential

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FORWARD BIAS

Applied voltage above0.7V depletion region is

removed charge carriers can flow

V< 0.7V V> 0.7V

P N

+ +

Depletion region

narrows as appliedvoltage approaches 0.7V

Depletion Region

DAERAH DEPLESI MENYEMPIT MENGHILANG

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REVERSE BIAS

Depletion region extends

Higher voltage Breakdown Current flow

V< 0V V

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PITA ENERGI SEBUAH ATOM

PITA HANTARAN

PITA VALENSI

CELAH ENERGI

INTI

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PITA ENERGI

PITA

HANTARAN

PITA VALENSI

PITA

HANTARAN

PITA VALENSI PITA VALENSI

PITAHANTARANLarge Gap

No Gap

Small Gap

SemiconductorsMetalsInsulators

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Elektron di orbit terluar

Silicon

Tetravalent

Boron

Trivalent

Acceptor

Phosphorus

Pentavalent

Donor

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PITA ENERGI

PITA HANTARAN

PITA VALENSIelektron

celah energi

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TERBENTUKNYA HOLE

elektron

PITA HANTARAN

ELEKTRONBEBAS

HOLE

ENERGI

TAMBAHAN

Jumlah Elektron Bebas = Jumlah Hole

PITA VALENSI

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p-type material


doped with acceptors.

Material has high holeconcentration

Concentration of free

electrons in p-type material

is very low.

n-type material


doped with donors.

Material has highconcentration of free

electrons.

Concentration of holes in

n-type material is very low.

P-N JUNCTION FORMATION

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p-type material

Contains

NEGATIVELY

charged acceptors

(immovable) andPOSITIVELY charged

holes (free).

Total charge = 0

n-type material

Contains POSITIVELY

charged donors

(immovable) and

NEGATIVELY

charged free electrons.

Total charge = 0

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p-type material

Contains

NEGATIVELY

charged acceptors

(immovable) andPOSITIVELY charged

holes (free).

Total charge = 0

n-type material

Contains POSITIVELY

charged donors

(immovable) and

NEGATIVELYcharged free electrons.

Total charge = 0

What happens if n- and p-type materials are in close contact?


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p- n junction formation


Being free particles, electrons start diffusing from n-type material into p-material

Being free particles, holes, too, start diffusing from p-type material into n-material

Have they been NEUTRAL particles, eventually all the free

electrons and holes had uniformly distributed over the entirecompound crystal.

However, every electrons transfers a negative charge (-q) ontothe p-side and also leaves an uncompensated (+q) charge of thedonor on the n-side.

Every hole creates one positive charge (q) on the n-side and (-q)-

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p- n junction formation


Electrons and holes remain staying close to the p-n junction becausenegative and positive charges attract each other.

Negative charge stops electrons from further diffusion

Positive charge stops holes from further diffusion

The diffusion forms a dipole charge layer at the p-n junction interface.

There is a built-in VOLTAGE at the p-n junction interface that prevents

penetration of electrons into the p-side and holes into the n-side.

p-type n-type

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p- n junction currentvoltage characteristics

What happens when the voltage is applied to a p-n junction?

The polarity shown, attracts holes to the left and electrons to the right.

According to the current continuity law,the current can onlyflow if all

the charged particles move forming a closed loop

However, there are very few holes in n-type material and there are

very few electrons in the p-type material.

There are very few carriers available to support the current through the

junction plane

For the voltage polarity shown, the current is nearly zero

p-type n-type

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p- n junction currentvoltage characteristics

What happens if voltage of opposite polarity is applied to a p-n junction?

The polarity shown, attracts electrons to the left and holes to the right.

There are plenty of electrons in the n-type material and plenty of holes in

the p-type material.

There are a lot of carriers available to cross the junction.

When the voltage applied is lower than the built-in voltage,

the current is still nearly zero

p-type n-type

When the voltage exceeds the built-in voltage, the current can flow through

the p-n junction

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Diode currentvoltage (I-V) characteristics

1

kT

qVII S exp

p n

Semiconductor diode consists of a p-n junction with two

contacts attached to the p- and n- sides

ISis usually a very small current, IS 10-1710-13A

When the voltage V is negative (reverse polarity) the exponential term -1;

The diode current is IS( very small).

0V

When the voltage V is positive (forward polarity) the exponential term

increases rapidly with V and the current is high.

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p-type material


doped with acceptors.

Material has high holeconcentration

Concentration of free

electrons in p-type material

is very low.

n-type material


doped with donors.

Material has highconcentration of free

electrons.

Concentration of holes in

n-type material is very low.

p-n junction formation

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IKATAN KOVALENT

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SILIKON DIPANASI

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DI DOPING ATOM BERVALENSI 5

ION POS

BAHAN

N

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BAHAN

P

ION NEG

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ION POS

BAHAN

N

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BAHAN

P

ION NEG

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BAGAIMANA MEMBUAT BAHAN N ?

Bahan silikon diberi doping atom bervalensi 5

(misal : pospor)

Uap pospor

Si N

Atom pospor disebut DONOR

RUANG HAMPA

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Bahan semikonduktor jenis P

Bahan silikon diberi doping atom bervalensi 3

(misal : boron)

Uap boron

Si P

Atom boron disebut ASEPTOR

RUANG HAMPA

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DISTRIBUSI HOLE

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TEGANGAN KONTAK

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Simbul dioda dan arah arus

Karakteristik ideal

Rangkaian ekivalen saat reverse bias Rangkaian ekivalen saat forward bias

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PENDEKATAN IDEAL

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p- n diode applications:

current rectifiers

1p

kT

qV

IS

1p

kT

qV

IS

+-

Time

Voltage

+

-

Time

Current

PENYEARAH

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PENYEARAH

setengah gelombang

Saat forward

Saat reverse

Tegangan input

Tegangan output

0 2

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TEGANGAN DC RATA-RATA

Mengintegralkan

satu periode

2

0sin2

1

dVV mDC

2

0

sin2

dV

V m

DC

0cos2

mDCV

V

mm

DC

VVV 11

2

2

VDC

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Bila ada tegangan lawan

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Contoh rangkaian dioda

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MELIHAT DETIL

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PENGARUH PANAS

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GARIS KERJA(load line)

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MODEL DIODA DENGAN rD

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DIODA TANPArD

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DIODA TANPArD

1 2 3

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1 2 3

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POWER SUPPLYCATU DAYA

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PENYEARAH

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PENYEARAH

GELOMBANG PENUH

TRAFO TANPA CENTER TAP

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TRAFO TANPA CENTER TAP

(PENYEARAH BRIDGE)

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FILTER C

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PENGARUH BEBAN RL

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RIPLE (RIAK)

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SUPERDIODA (PENYEARAH PRESISI)

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CLIPPER (PEMANGKAS)

Vin: tegangan sinus

VoutVin

D1

D2

L+ L-

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PENGGESER DAN PENGARUH R

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PENGGESER DAN PENGARUH R

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PENGGANDA TEGANGAN

TEGANGAN PADA D1

PENGHASIL TEGANGAN GANDA

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PENGHASIL TEGANGAN GANDA

(DUAL SUPPLY)

Documents

KUL-ELDAS4-07