Bahan Kuliah Minggu ke 6 ELEKTRONIKA DASAR Jurusan

Bahan Kuliah Minggu ke 6 ELEKTRONIKA DASAR Jurusan Teknik Elektro FT-UGM 2007 1

DIODA DAYA Typical medium power diode Diode symbol and ideal current– voltage characteristic. 2

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beban Vmax Imax Bentuk gelombang output Tegangan dan arus beban Tegangan dioda 4

THYRISTOR Thyristor or silicon controlled rectifier (SCR) symbol. Thyristor current–voltage characteristics. 5

STRUKTUR THYRISTOR 6

Bentuk gelombang • Gelombang tegangan beban • Gelombang tegangan thyristor 7

Bentuk gelombang • Gelombang tegangan beban • Gelombang tegangan dan arus thyristor 8

Bentuk fisik thyristor Two flat-pack thyristors mounted on a liquid cooled heat sink 9

Thyristor sbg saklar S 1 S 2 10

FORCED COMMUTATION NO NO : Normally Open NC : Normally Closed Memutus arus NC NO NO Menghubung singkat thyristor 11

SWITCHED OFF • Thyristor harus dipaksa OFF dgn capasitor 12

SWITCHED OFF • Pemaksa an lewat thyristor 2 13

PENGUJIAN THYRISTOR 14

Thyristor di trigger lewat cahaya Light-fired thyristor used for HVDC transmission. 15

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Controllable rectifiers Single-phase thyristor-controlled bridge rectifier. 17

Operation of the single-phase thyristor-controlled bridge rectifier (b) Negative ac supply cycle (a) Positive ac supply cycle • Operation – Thyristor 1 & 2 fired in the positive cycle – Thyristor 3 & 4 fired in the negative cycle. 18

Controllable rectifiers (a) AC voltage, current and thyristor voltage DC voltage is controlled by the delay of firing delay (b) DC voltage, current and gate pulse Voltage and current waveforms of the singlephase thyristor-controlled bridge rectifier 19

Operation Concept Bridge Inverters Current flow when S 1 and S 2 are conducting Current flow when S 3 and 1. S 4 are conducting Bridge operation generated voltage waveform. Purpose: Converts DC to AC 20

RMS value of the output voltage and operation frequency Bridge Inverters 21

GTO (Gate Turn-Off thyristor( Vmax = 4, 500 V, Imax = 3, 000 A, Von = 2 -3 V Thyristor Vmax = 7, 000 V, Imax = 4, 000 A, Von = 1. 5 -3 V 22

GTO Gate turn-off thyristor (GTO) symbol. Gate turn-off thyristor (GTO) operation. 23

Bidirectional Triode Thyristor ( TRIAC) • 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 MT 1 dan MT 2 positif terhadap terminal MT 1. • TRIAC dapat dimatikan dengan memberikan sinyal gerbang positip antara gerbang G dan MT 1. Jika terminal MT 2 negatif terhadap MT 1, maka TRIAC akan dapat dihidupkan dengan memberikan sinyal pulsa negatif antara gerbang G dan terminal MT 1. • Tidak perlu untuk memiliki kedua sinyal gerbang positif dan negatif sehingga TRIAC dapat dihidupkan baik oleh sinyal gerbang positif maupun negatif. • Simbol TRIAC 24

• 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 d. V/dt, which is the rate of rise of voltage with respect to time. A triac can be switched into conduction by a large d. V/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 d. V/dt 25

Triode Alternating Current Switch TRIAC 26

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DIMMER 29

komponen R 1 1 50 K Pot R 2 1 15 K 1/2 W Resistor C 1, C 2 2 0. 068 250 V Capacitor L 1 1 Lamp To Be Controlled (up to 350 watts) L 2 1 Neon Lamp TR 1 1 40502 TRIAC 30

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DIAC merupakan salah satu jenis dioda SCR, namun memiliki dua terminal (elektroda) saja, 32

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. 33

Triac Light Dimmer Light bulb a b Triac (front view) 3. 3 kΩ + Van (from Variac) – c Bilateral trigger diode (diac) n + Van – n Light bulb + 0 V – • Efficient Triac G MT 1 0. 1µF a • Simple MT 2 250 kΩ linear pot + Van – 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. 3 kΩ resistor is ignored in this diagram. • Inexpensive MT 1 MT 2 G a b • Ingenious + Van – n Light bulb + Van – b + 0 V – After firing, the triac is a closed switch, so that practically all of Van is applied across the light bulb. 34

• Triac Closed Triac Open When the voltage across the diac reaches about ± 35 V, it self-fires and its voltage collapses to about ± 5 V Light bulb 3. 3 kΩ + Van (from Variac) – 250 kΩ linear pot 0. 1µF Bilateral trigger diode (diac) + Van (from Variac) – Capacitor discharges into triac gate Light bulb 3. 3 kΩ 250 kΩ linear pot 0. 1µF Bilateral trigger diode (diac) • Light bulb resistance is a few ohms when cold, and about 100 -200Ω when bright (use to get R) • The light bulb resistance is small compared to the 3. 3 kΩ and potentiometer combination and can be ignored when analyzing the RC electronic circuit • The circuit resets and the process repeats every half-cycle of 60 Hz 35

Hookup Variac Isolation transformer Light dimmer 36

No-Firing Condition – Actual Variac voltage Capacitor voltage • When potentiometer resistance is large, there is no firing because the capacitor voltage never exceeds (positive or negative) the diac breakover voltage • Capacitor voltage lags variac voltage almost 90º for large potentiometer resistance 37

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 38

TERMISTOR 39

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. 40

LDR 41

UNTAI LDR 42

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• LDR consists of a slab of bulk semiconducting material – cadmium sulphide (Cd. S) or cadmium selenide (Cd. Se) – 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-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 44

Calculate the cut-off wavelengths of intrinsic Cd. S, Cd. Se and Pb. S LDR's, for respective excitation energies of 2. 4, 1. 7 and 0. 4 e. V. • • Solution For Cd. S, the excitation energy in Joules is, – Wmin = 2. 4 e. V x 160 x 10 -21 J e. V-1 – = 384 x 10 -21 J • The cut-off wavelength is – max = hc/Wmin – = (663 x 10 -36 Js x 300 x 106 m s-1) / 384 x 10 -21 J – = 520 nm • Detector will respond only to light in blue-green part of the spectrum. – Similarly for Cd. Se, max is 720 nm and will respond to all visible wavelengths – Pb. S, with a cut-off at 3 m, is sensitive out to the infra-red. 45

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• Photoconductive 1. 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 48