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

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

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4 Bentuk gelombang output Tegangan dan arus beban Tegangan dioda V max I max beban

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

6 STRUKTUR THYRISTOR

7 Bentuk gelombang Gelombang tegangan beban Gelombang tegangan thyristor

8 Bentuk gelombang Gelombang tegangan beban Gelombang tegangan dan arus thyristor

9 Bentuk fisik thyristor Two flat-pack thyristors mounted on a liquid cooled heat sink Figure 9.14Demonstration of thyristor operat

10 Thyristor sbg saklar S1 S2

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

12 SWITCHED OFF Thyristor harus dipaksa OFF dgn capasitor

13 SWITCHED OFF Pemaksa an lewat thyristor 2

14 PENGUJIAN THYRISTOR

15 Thyristor di trigger lewat cahaya Light-fired thyristor used for HVDC transmission. Figure 9.14Demonstration of thyristor operat

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17 Controllable rectifiers Figure 9.14Demonstration of thyristor operat Single-phase thyristor-controlled bridge rectifier.

18 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 (a) Positive ac supply cycle. (b) Negative ac supply cycle

19 Controllable rectifiers Figure 9.14Demonstration of thyristor operat (a) AC voltage, current and thyristor voltage 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

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

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

22 GTO Thyristor Vmax = 7,000 V, Imax = 4,000 A, Von = 1.5-3V GTO (Gate Turn-Off thyristor) Vmax = 4,500 V, Imax = 3,000 A, Von = 2-3V

23 GTO Gate turn-off thyristor (GTO) symbol. Figure 9.14Demonstration of thyristor operat Gate turn-off thyristor (GTO) operation.

24 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)

25 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

26 Triode Alternating Current Switch TRIAC

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29 DIMMER

30 komponen R1150K Pot R2115K 1/2W Resistor C1, C V Capacitor L11Lamp To Be Controlled (up to 350 watts) L21Neon Lamp TR TRIAC

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

33 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.

34 Triac Light Dimmer Triac (front view) MT1 MT2 G + V an (from Variac) – Light bulb G MT2 MT1 0.1µF 3.3kΩ 250kΩ linear pot Triac Bilateral trigger diode (diac) a c n b Light bulb a 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 – + V an – + V an – Ingenious Simple Efficient Inexpensive After firing, the triac is a closed switch, so that practically all of V an is applied across the light bulb. Light bulb a n b + V an – + V an – + 0V –

35 Triac Open + V an (from Variac) – Light bulb 0.1µF 3.3kΩ 250kΩ linear pot Bilateral trigger diode (diac) Light bulb resistance is a few ohms when cold, and about Ω when bright (use to get R) 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 + V an (from Variac) – Light bulb 0.1µF 3.3kΩ 250kΩ linear pot Bilateral trigger diode (diac) Triac Closed

36 Hookup Isolation transformer Variac Light dimmer

37 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

38 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

39 TERMISTOR

40 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.

41 LDR

42 UNTAI LDR

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44 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-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

45 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, –W min = 2.4 eV x 160x J eV -1 – = 384 x J The cut-off wavelength is – max = hc/W min – = (663x Js x 300x10 6 m s -1 ) / 384x 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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48 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