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ELEKTRONIKA DASAR

Jurusan Teknik Elektro

FT-UGM

2007

Bahan Kuliah Minggu ke 6

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DIODA DAYA

V

I

Vbreakdown

Reverse biasregion

Forward biasregion

Anode Cathode

I

V

Diode symbol and ideal current–voltage characteristic.

Typical medium power diode

3

4

Bentuk gelombang

output

VloadVac

Iload

Rload

Vdiode

0 90 180 270 360 450 5400

20

40

60

80

100

Vload t( )

V

Iload t( )

A

t

deg

0 90 180 270 360 450 540100

80

60

40

20

0

20

40

60

80

100

Vac t( )

V

Vdiode t( )

V

t

deg

Tegangan dan

arus beban

Tegangan dioda

Vmax

Imax

beban

5

THYRISTOR

Gate

CathodeAnode

Igate

VACat

IAThyristor or

silicon controlled rectifier (SCR) symbol.

Forward onstate

Ano

de c

urre

nt

Anode-Cathode voltage

Reverse bias Forward bias

Reversebreakdown

voltage

Forward breakdown voltage (VFB) vs.gate current

ig0 = 0ig1ig2ig3ig4

Thyristor current–voltage characteristics.

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STRUKTUR THYRISTOR

ANODE

PINTU

KATODE

P

PN

P

PN

PNPN

IAIB1 IGn

IC2

IKIB2IGp

IC1

A

K

J1

J2

J3

7

Bentuk gelombang

• Gelombang tegangan beban

Vgate Rload

Iload

Vac

Vthy

Vload

0 90 180 270 360 450 5400

20

40

60

80

100

Vload t( )

V

Iload t( )

A

t

deg

0 90 180 270 360 450 540100

80

60

40

20

0

20

40

60

80

100

Vac t( )

V

Vthy t( )

V

Vgate t( )

V

t

deg

• Gelombang tegangan thyristor

8

Bentuk gelombang

• Gelombang tegangan beban

Vgate Rload

Iload

Vac

Vthy

Vload

0 90 180 270 360 450 5400

20

40

60

80

100

Vload t( )

V

Iload t( )

A

t

deg

0 90 180 270 360 450 540100

80

60

40

20

0

20

40

60

80

100

Vac t( )

V

Vthy t( )

V

Vgate t( )

V

t

deg

• Gelombang tegangan dan arus thyristor

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Bentuk fisik thyristor

Two flat-pack thyristors

mounted on a liquid

cooled heat sink

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Thyristor sbg saklar

S1

S2

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FORCED COMMUTATION

NONC NONO

Memutus arus Menghubung singkat thyristor

NO : Normally OpenNC : Normally Closed

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SWITCHED OFF

• Thyristor harus dipaksa OFF

dgn capasitor

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SWITCHED OFF

• Pemaksaan lewat thyristor 2

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PENGUJIAN THYRISTOR

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Thyristor di trigger lewat cahaya

Light-fired thyristor used for HVDC transmission.

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17

Controllable rectifiers

VacVdc

AC

Th4

Th1

Th2

Th3

Vac

Single-phase thyristor-controlled bridge rectifier.

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Operation of the single-phase

thyristor-controlled bridge rectifier

• Operation– Thyristor 1 & 2 fired in the positive cycle– Thyristor 3 & 4 fired in the negative cycle

Vth Iac

Idc

Vac

Vdc

Th4

Th1

Th2

Th3

AC

(a) Positive ac supply cycle

Vth

Iac

Idc

Vac

Vdc

AC

Th4

Th1

Th2

Th3

.

(b) Negative ac supply cycle

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Controllable rectifiers

0 60 120 180 240 300 360180

120

60

0

60

120

180

Vac t( )

V

Iac t( )

A

Vth t( )

V

tdeg

(a) AC voltage, current and thyristor voltage

0 60 120 180 240 300 3600

30

60

90

120

150

180

Vdc t( )

V

Idc t( )

A

Vgate t( )

V

t

deg

Voltage and current waveforms of the single-phase thyristor-controlled bridge rectifier

(b) DC voltage, current and gate pulse

DC voltage is controlled by the delay of firing

delay

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Operation Concept Bridge Inverters

TonVac(t)

t

B

A

Tcyc(c)

Ton

Vdc

-Vdc

Vdc

Vac

Idc

Rload

S1

S2

Iac

Iac

Idc

(b)S4

S3

Vdc

Vac

Idc

Rload

S1

S2

Iac

Iac

Idc

(a)

S3

S4

Purpose: Converts DC to AC

Current flow when S1 and

S2 are conducting

Bridge operationgenerated voltage waveform.

Current flow when S3 and

S4 are conducting

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RMS value of the output voltage and operation frequency

Bridge Inverters

cyc

ondc

T

dccyc

acrms T

TVdtV

TV

on

22

0

2_

cycac Tf

1

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GTO

ThyristorVmax = 7,000 V, Imax = 4,000 A, Von = 1.5-3V

GTO ( -Gate Turn Of f thyristor)

Vmax = 4,500 V, Imax = 3,000 A,

Von = 2-3V

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GTO

Gate turn-off thyristor (GTO) symbol.

Gate

CathodeAnode

Igate

VACat

IA

Vgate Rload

Iload

Vac

VGTO

Vload

0 90 180 270 360 450 5400

20

40

60

80

100

Vload t( )

V

Iload t( )

A

t

deg

0 90 180 270 360 450 540100

75

50

25

0

25

50

75

100

Vac t( )

V

VGTO t( )

V

VGate t( )

V

t

deg

Gate turn-off thyristor (GTO) operation.

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• TRIAC dapat bersifat konduktif dalam dua arah. Dapat dianggap dua buah thyristor tersambung secara antiparalel dengan koneksi gerbang. Untuk pengendalian tegangan AC

• Karena TRIAC merupakan devais bidirectional, terminalnya tidak disebut anode/katode tetapi terminal MT1 dan MT2. MT2 positif terhadap terminal MT1.

• TRIAC dapat dimatikan dengan memberikan sinyal gerbang positip antara gerbang G dan MT1. Jika terminal MT2 negatif terhadap MT1, maka TRIAC akan dapat dihidupkan dengan memberikan sinyal pulsa negatif antara gerbang G dan terminal MT1.

• Tidak perlu untuk memiliki kedua sinyal gerbang positif dan negatif sehingga TRIAC dapat dihidupkan baik oleh sinyal gerbang positif maupun negatif.

• Simbol TRIAC

Bidirectional Triode Thyristor ( TRIAC)

MT2

MT1

G

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• Obviously a triac can also be triggered by exceeding the breakover voltage. This is not normally employed in triac operation. The breakover voltage is usually considered a design limitation. One other major limitation, as with the SCR, is dV/dt, which is the rate of rise of voltage with respect to time. A triac can be switched into conduction by a large dV/dt. Typical applications are in phase control, inverter design, AC switching, relay replacement, etc.

• Major considerations when specifying a triac are:(a) Forward and reverse breakover voltage.(b)Maximum current(c) Minimum holding current(d) Gate voltage and gate current trigger requirements.(e) Switching speed(f) Maximum dV/dt

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Triode Alternating Current Switch TRIAC

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DIMMER

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komponen

R1 1 50K Pot

R2 1 15K 1/2W Resistor

C1, C2 2 0.068 250V Capacitor

L1 1 Lamp To Be Controlled (up to 350 watts)

L2 1 Neon Lamp

TR1 1 40502 TRIAC

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DIAC

DIAC merupakan salah satu jenis dioda SCR, namun memiliki dua terminal (elektroda) saja,

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KARAKTERISTIK DIAC

• The diac is a bidirectional trigger diode which is designed specifically to trigger a triac or SCR.

• Basically the diac does not conduct (except for a small leakage current) until the breakover voltage is reached.

• Typically about 5 volts, creating a breakover current sufficient to trigger a triac or SCR.

Typical diacs have a power dissipations ranging from 1/2 to 1 watt.

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Triac Light Dimmer

Triac(front view)

MT1 MT2 G

+Van

(from Variac)–

Lightbulb

G

MT2

MT1

0.1µF

3.3kΩ

250kΩ linear pot

Triac

Bilateral trigger diode

(diac)

a

c

n

b

Lightbulba

n

b

Before firing, the triac is an open switch, so that practically no voltage is applied across the light bulb. The small current through the 3.3kΩ resistor is ignored in this diagram.

+ 0V –+Van

–

+Van

–

•Ingenious

•Simple

•Efficient

•Inexpensive

After firing, the triac is a closed switch, so that practically all of Van is applied across the light bulb.

Lightbulba

n

b

+ Van –+

Van

–

+0V–

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Triac Open

+Van

(from Variac)–

Lightbulb

0.1µF

3.3kΩ

250kΩ linear pot

Bilateral trigger diode

(diac)

• Light bulb resistance is a few ohms when cold, and about 100-200Ω when bright (use to get R)RPVrms /2

• The light bulb resistance is small compared to the 3.3kΩ and potentiometer combination and can be ignored when analyzing the RC electronic circuit

When the voltage across the diac reaches about ±35V, it self-fires and its voltage

collapses to about ± 5V

• The circuit resets and the process repeats every half-cycle of 60Hz

Capacitor discharges into triac gate

+Van

(from Variac)–

Lightbulb

0.1µF

3.3kΩ

250kΩ linear pot

Bilateral trigger diode

(diac)

• Triac Closed

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Hookup

Isolation transformer

Variac

Light dimmer

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No-Firing Condition – Actual

• When potentiometer resistance is large, there is no firing because the capacitor voltage never exceeds (positive or negative) the diac breakover voltage

Variac voltage

Capacitor voltage

• Capacitor voltage lags variac voltage almost 90º for large potentiometer resistance

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Firing Condition – Actual

• Capacitor voltage Vcn does not go into steady state AC right away as Van crosses the zero axis. There is a time delay due to the RC time constant.

• The RC time constant delay plus phase shift of the AC solution for Vcn determines the point at which the diac breakover is achieved

Van Vcn

α = 90° ≈ 16.67ms ÷ 4

Diac conducts when Vcn

reaches 32-35V (diac breakover voltage). The capacitor then discharges through the triac gate.

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TERMISTOR

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Light-dependent resistors• The simplest of the photoconductive devices is the

light-dependent resistor or LDR.• It is typically used in a voltage divider circuit. • LDRs are cheap and simple to use, but are slow to

respond to changes in light intensity and are often not suitable for high-speed computer applications.

• Due to its relatively large size and power requirements, the LDR tends not to be used for data signal production, but it has a use in applications such as simple alarm circuits and detectors on production lines.

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LDR

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UNTAI LDR

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• LDR consists of a slab of bulk semiconducting material– cadmium sulphide (CdS) or cadmium selenide (CdSe)– a pair of electrical contacts across its ends

• Incident light creates electron-hole pairs– minimum photon energy needed to excite electrons

• will only respond to light below a maximum value– Long wavelength cut-offLong wavelength cut-off

c = hc/Wmin– The increased number of electrons & holes available

for conduction provide an increase in the conductivity of material

• a decrease in the resistivity of the material• a voltage in series with a load resistor is applied across

semiconductor to pull electrons and holes to respective terminals

– Response times of LDR's depend purely on the drift of the photon-generated carriers to their respective electrodes relatively long with 50 ms being fairly typical

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Calculate the cut-off wavelengths of intrinsic CdS, CdSe and PbS LDR's, for respective excitation energies of 2.4, 1.7 and 0.4 eV.

• Solution• For CdS, the excitation energy in Joules is,

– Wmin = 2.4 eV x 160x10-21 J eV-1

– = 384 x 10-21 J

• The cut-off wavelength is– max = hc/Wmin

– = (663x10-36 Js x 300x106 m s-1) / 384x10-21 J– = 520 nm

• Detector will respond only to light in blue-green part of the spectrum.– Similarly for CdSe, max is 720 nm and will respond to all visible

wavelengths– PbS, with a cut-off at 3 m, is sensitive out to the infra-red.

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• Photoconductive1. such devices do not produce

electricity, but simply change their resistance

2. photodiode (as described earlier) can be used in this way to produce a linear device

3. phototransistors act like photodiodes but with greater sensitivity

4. light-dependent resistors (LDRs) are slow, but respond like the human eye