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Kuliah Elektronika Dasar Minggu ke 4

DIODA

Jurusan Teknik ElektroFakultas Teknik UGM

2007

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FUNCTION

Electrical ‘gate’ Current only flows one way

Forward biased Current flows

Reverse biased Blocks current

+ -

- +

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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 voltageC

urr

en

t

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-type material n-type material

SAMBUNGAN PN

Holes diffuse into the n-type and ‘swallow’ electrons

Electrons diffuse into the p-type and ‘fill holes’

Depletion region formed

No free charge carriers 0.7V contact potential

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FORWARD BIAS

Applied voltage above 0.7V depletion region is

removed charge carriers can flow

V< 0.7V V> 0.7V

P N

+ +

Depletion region narrows as applied voltage approaches 0.7V

Depletion Region

DAERAH DEPLESI MENYEMPIT MENGHILANG

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REVERSE BIAS

Depletion region extendsHigher voltage

Breakdown Current flow

V< 0V V<< 0V+ +

DAERAH DEPLESI MELEBAR MAKIN LEBAR

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Bohr model(I hope it’s not bohring)

The Bohr model is a planetary model, where the electron orbits the nucleus like a planet orbits the Sun.

An electron is only allowed in DISCRETE orbits (n=1, n=2, n=3, etc.)

The higher the orbit, the higher the energy of the electron.

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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

PITA HANTARAN Large Gap

No Gap

Small Gap

Semiconductors Metals Insulators

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Elektron di orbit terluar

SiliconTetravalent

BoronTrivalent

“Acceptor”

PhosphorusPentavalent

“Donor”

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PITA ENERGI

PITA HANTARAN

PITA VALENSIelektron

celah energi

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TERBENTUKNYA HOLE

elektron

PITA HANTARAN

ELEKTRON BEBAS

HOLE

ENERGI

TAMBAHAN

Jumlah Elektron Bebas = Jumlah Hole

PITA VALENSI

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p-type material

Semiconductor material doped with acceptors.

Material has high hole concentration

Concentration of free electrons in p-type material is very low.

n-type material

Semiconductor material doped with donors.

Material has high concentration of free electrons.

Concentration of holes in n-type material is very low.

P-N JUNCTION FORMATION

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P-N JUNCTION FORMATION

p-type material

Contains NEGATIVELY charged acceptors (immovable) and POSITIVELY 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) and POSITIVELY charged holes (free).

Total charge = 0

n-type material

Contains POSITIVELY charged donors (immovable) and NEGATIVELY charged free electrons.

Total charge = 0

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

P-N JUNCTION FORMATION

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p- n junction formation

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

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 entire compound crystal.

However, every electrons transfers a negative charge (-q) onto the p-side and also leaves an uncompensated (+q) charge of the donor on the n-side. Every hole creates one positive charge (q) on the n-side and (-q) on the p-side

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p- n junction formation

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

Electrons and holes remain staying close to the p-n junction because negative 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 current – voltage characteristicsWhat 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 only flow 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 current – voltage 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 current – voltage (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

IS is usually a very small current, IS ≈ 10-17 …10-13 A

When the voltage V is negative (“reverse” polarity) the exponential term ≈ -1; The diode current is ≈ IS ( very small).

0 V

When the voltage V is positive (“forward” polarity) the exponential term increases rapidly with V and the current is high.

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Δίοδος

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p-type material

Semiconductor material doped with acceptors.

Material has high hole concentration

Concentration of free electrons in p-type material is very low.

n-type material

Semiconductor material doped with donors.

Material has high concentration 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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DI DOPING ATOM BERVALENSI 3

BAHAN P

ION NEG

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DI DOPING ATOM BERVALENSI 5

ION POS

BAHAN N

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DI DOPING ATOM BERVALENSI 3

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

1exp

kT

qVII S

IS

1exp

kT

qVII S

IS

+-

Time

Voltage+-

Time

Current

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PENYEARAH setengah gelombang

Saat forward

Saat reverse

Tegangan input

Tegangan output

0 π 2π

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TEGANGAN DC RATA-RATA

Mengintegralkan satu periode

2

0

sin2

1dVV mDC

2

0

sin2

dV

V mDC

0cos

2 m

DC

VV

mmDC

VVV 11

2

2π

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 TANPA rD

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DIODA TANPA rD

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1 2 3

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POWER SUPPLYCATU DAYA

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PENYEARAH GELOMBANG PENUH

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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

VoutVinD1 D2L+ L-

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PR

Vin adalah tegangan kotak ± 10 Volt

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PENGGESER DAN PENGARUH R

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PENGGANDA TEGANGAN

TEGANGAN PADA D1

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PENGHASIL TEGANGAN GANDA(DUAL SUPPLY)