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TE-UGM-2007TE-UGM-2007 11
Jurusan Teknik ElektroJurusan Teknik Elektro
UGMUGM
20072007
SPECIAL DIODESSPECIAL DIODES
Bahan Kuliah minggu ke 5Bahan Kuliah minggu ke 5
Elektronika DasarElektronika Dasar
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Zener DiodesZener Diodes
A zener is used in reverse breakdown mode
The voltage across a zener is more or less independent of the current through it
The function of a zener is to provide a voltage reference in a circuit
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ZENER CHARACTERISTICZENER CHARACTERISTICA zener diode is much like a normal diode. The exception being is that it is placed in the circuit in reverse bias and operates in reverse breakdown.
Operation region
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Some important characteristics:Some important characteristics: Nominal Zener Voltage :
5.1V zener, 12V zener, etc.
Nominal Bias Current: the Iz to get the nominal Vz
Tolerance on zener voltage, e.g. : 12V 5%,
Maximum Power: 1Watt zener, 5 Watt zener, etc.
Temperature coefficient: by what % does zener voltage change as diode temp. changes
1OC Dynamic Resistance (Rd):
Rd = V/ I
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Zener Operation RegionZener Operation Region• Zeners are
available with voltage breakdowns of 1.8 V to 200 V.
• This curve illustrates the minimum and maximum ranges of current operation that the zener can effectively maintain it’s voltage.
∆V
∆I
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Basic Zener CircuitBasic Zener Circuit
Key points:Key points: VVin > V > Vz
IIT = (V = (Vinin – V – Vzz)/R)/Rss I ILL+I+IZZ
IT
IZ IL
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Calculation: Find RCalculation: Find RSuppose a 5.1 Volt zener is connected to a 12 Volt supply Suppose a 5.1 Volt zener is connected to a 12 Volt supply
through a resistor. The zener requires a 15 mA bias, and through a resistor. The zener requires a 15 mA bias, and the load is 510 Ohms. Find the required resistor value.the load is 510 Ohms. Find the required resistor value.
load current: Iload current: ILL = 5.1V / 510 = 5.1V / 510 = 10 mA = 10 mA total current: Itotal current: ITT = I = ILL + I + IZZ = (10 + 15) = 25 = (10 + 15) = 25
mA mA drop across R: Vdrop across R: VRR = 12V – 5.1V = 6.9 V = 12V – 5.1V = 6.9 V R value : R = VR value : R = VRR / I / ITT = 6.9 V / 25 mA = = 6.9 V / 25 mA =
276 Ohms276 Ohms Select standard value resistor: R = 270 Select standard value resistor: R = 270
OhmsOhms
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DATA SHEETDATA SHEET
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Zener Diode ApplicationsZener Diode ApplicationsRegulation
In this simple illustration of zener regulation circuit, the zener diode will “adjust” it’s impedance based on varying input voltages and loads (RL) to be able to maintain it’s designated zener voltage. Zener current will increase or decrease directly with voltage input changes. The zener current will increase or decrease inversely with varying loads. Again, the zener has a finite range of operation.
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A 10 V zener has 20 mA of bias current. A 10 V zener has 20 mA of bias current. The load resistor across the zener is 20 The load resistor across the zener is 20 Ohms. Ohms. What power rating should the What power rating should the zener havezener have? Remember: if the load is ? Remember: if the load is removed, all current is in the zener.removed, all current is in the zener.
Find total current: Find total current: • IIT = I= IBIAS + I + ILOAD = 20mA + 50mA = 70 mA = 20mA + 50mA = 70 mA
Find power in zener (Pz) at a current (Iz) Find power in zener (Pz) at a current (Iz) = 70 mA:= 70 mA:
• PPz = V= Vz I Iz = 10V = 10V 70ma = 700 mW 70ma = 700 mW Double value for reliability:Double value for reliability:
• Use a zener rated for 1.5 Watts or higherUse a zener rated for 1.5 Watts or higher
Calculation: Find PMAXCalculation: Find PMAX
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TroubleshootingTroubleshootingAlthough precise power supplies typically use IC type regulators, zener diodes can be used alone as a voltage regulator.
A properly functioning zener will work to maintain the output voltage within certain limits despite changes in load.
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Zener LimitingZener Limiting
Zener diodes can be used as limiters. The difference to consider for a zener limiter is a it’s zener breakdown characteristics.
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Voltage Surge ProtectorsVoltage Surge Protectors
Fast, high-voltage transients, called “spikes”, on Fast, high-voltage transients, called “spikes”, on AC power lines can damage electronic equipment.AC power lines can damage electronic equipment.
Back-to-back zeners can clip off the spikes.Back-to-back zeners can clip off the spikes.
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Varactor DiodesVaractor Diodes
A reverse-biased PN junction makes a A reverse-biased PN junction makes a
voltage-controlled capacitorvoltage-controlled capacitor
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Fig 3.12 Capacitance range: from 50 pF to 500 pFFig 3.12 Capacitance range: from 50 pF to 500 pF
Varactor CapacitanceVaractor Capacitance
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Varactor DiodesVaractor Diodes
A varactor diode is best explained as a variable capacitor. Think of the depletion region a variable dielectric. The diode is placed in reverse bias. The dielectric is “adjusted” by bias changes.
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Calculation: C & fRCalculation: C & fR If the varactor of figure 3.12 is If the varactor of figure 3.12 is
biased at Vbiased at VRR =5 V. =5 V.1.1. Find the capacitance from the graph.Find the capacitance from the graph.2.2. Find the resonant frequency with a 253 Find the resonant frequency with a 253
uH inductor.uH inductor.
From the graph, C = 100 pF.From the graph, C = 100 pF. Resonant frequency fResonant frequency fR = 1/(2 = 1/(2LC) LC)
= 1.0 MHz= 1.0 MHz
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Varactor TunerVaractor Tuner
Similar tuners are used in TVs, cell-phones, etc.Similar tuners are used in TVs, cell-phones, etc.
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Varactor DiodesVaractor DiodesThe varactor diode can be useful in filter circuits as the adjustable component.
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The PIN DiodeThe PIN Diode
Usable at high-frequenciesUsable at high-frequencies
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PIN DIODE
The pin diode is also used in mostly microwave frequency applications. It’s variable forward series resistance characteristic is used for attenuation, modulation, and switching. In reverse bias exhibits a nearly constant capacitance.
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Not a PN junctionNot a PN junction Fast, but reverse breakdown voltage Fast, but reverse breakdown voltage
less than 50 Vless than 50 V
Schottky DiodesSchottky Diodes
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Schottky diode
The Schottky diode’s significant characteristic is it’s fast switching speed. This is useful for high frequencies and digital applications. It is not a typical diode in the fact that it does not have a p-n junction, instead it consists of a heavily doped n-material and metal bound together.
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TUNNEL Diode TUNNEL Diode
The tunnel diode has negative resistance. It will actually conduct well with low forward bias.
With further increases in bias it reaches the negative resistance range where current will actually go down. This is achieved by heavily doped p and n materials that creates a very thin depletion region.
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TUNNEL DIODE CHARACTERISTICTUNNEL DIODE CHARACTERISTIC
The step-recovery diode is also used for fast switching applications.
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LASER DIODE
The laser diode (light amplification by stimulated emission of radiation) produces a monochromatic (single color) light. Laser diodes in conjunction with photodiodes are used to retrieve data from compact discs.
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Laser is an abbreviation of …... Laser is an abbreviation of …...
LLight ight AAmplification by mplification by SStimulated timulated EEmission of mission of RRadiationadiation• ““Stimulated emission”Stimulated emission”
antonym of “spontaneous emission”antonym of “spontaneous emission”• optical transition stimulated by the effect of optical transition stimulated by the effect of
electric field of light waveelectric field of light waveon the contrary usually emission occur on the contrary usually emission occur spontaneously without help of electric fieldspontaneously without help of electric field
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What is the difference between LED and LD?What is the difference between LED and LD?
LED is light emitting diodeLED is light emitting diode LD is laser diodeLD is laser diode
• Diode is a semiconductor device which has Diode is a semiconductor device which has an effect of rectificationan effect of rectification
• Both LED and LD are semiconductor diode Both LED and LD are semiconductor diode with a forward bias. Both emit lightwith a forward bias. Both emit light
• LED emits light by LED emits light by spontaneous emissionspontaneous emission mechanism, while LD has an mechanism, while LD has an optical cavityoptical cavity which enables multiplication of photon by which enables multiplication of photon by stimulated emission stimulated emission
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Explain how the light is transmitted Explain how the light is transmitted through optical fiber.through optical fiber.
Light is transmitted along the core by Light is transmitted along the core by total reflection mechanism at the total reflection mechanism at the boundary with the cladding layerboundary with the cladding layer
N=1.46
N=1.48
cladding
core
Light Ray EnteringCore from Air
Light is propagated by Total internal reflection
CROSS SECTION
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LEDs: Light Emitting DiodesLEDs: Light Emitting Diodes
Brightness proportional to currentBrightness proportional to current Colors: red, white, blue, green, orange, yellowColors: red, white, blue, green, orange, yellow Drop across an LED is about 1.5 VoltsDrop across an LED is about 1.5 Volts
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Optical DiodesOptical Diodes
The light-emitting diode (LED) emits photons as visible light. It’s purpose is for indication and other intelligible displays. Various impurities are added during the doping process to vary the color output.
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How much power does an LED How much power does an LED consume if it requires consume if it requires 25 mA25 mA and and has a forward drop of has a forward drop of 2.0 2.0 Volts?Volts?
P = V P = V I = 2V I = 2V .025A = 50 .025A = 50 mWmW
Calculation: Power in an LEDCalculation: Power in an LED
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Bright, but consumes a lot of powerBright, but consumes a lot of power Typically multiplexed to conserve powerTypically multiplexed to conserve power
THE 7-SEGMENT DISPLAYTHE 7-SEGMENT DISPLAY
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7 SEGMENT DISPLAY 7 SEGMENT DISPLAY The seven segment display is an example of LEDs use for display of decimal digits.
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How much power would a 4-digit 7-How much power would a 4-digit 7-segment LED display consume if each LED segment LED display consume if each LED required required 10 mA10 mA and had a forward drop of and had a forward drop of 1.5 1.5 Volts?Volts?
Power in one LEDPower in one LED: : • PPLED = V = V I = 2V I = 2V .01A = 20 mW .01A = 20 mW• Assume all segments are lit, then:Assume all segments are lit, then:
Power in a Digit: Power in a Digit: • PD = 7 PD = 7 PLED = 7 PLED = 7 20mW = 140 mW 20mW = 140 mW
Total Power: Total Power: • PT = 4 PT = 4 PD = 4 PD = 4 140 mW = 560 mW 140 mW = 560 mW
That’s over half a Watt!That’s over half a Watt!
Power in a 7-Segment DisplayPower in a 7-Segment Display
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Multiplexing to Reduce PowerMultiplexing to Reduce Power
Suppose a 4-digit display requires Suppose a 4-digit display requires 400 mW if all segments are lit. If the 400 mW if all segments are lit. If the display is multiplexed so that each digit is display is multiplexed so that each digit is lit in a continuous sequence lit in a continuous sequence (1,2,3,4,1,2,3,4...) how much power would (1,2,3,4,1,2,3,4...) how much power would the display use?the display use?
Since each digit is on for only 25% of the Since each digit is on for only 25% of the time,time,
P = 0.25 P = 0.25 400 mW = 100 mW 400 mW = 100 mW
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TroubleshootingTroubleshootingAlthough precise power supplies typically use IC type regulators, zener diodes can be used alone as a voltage regulator.
A properly functioning zener will work to maintain the output voltage within certain limits despite changes in load.
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DIODA FOTODIODA FOTO
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Fig. Fig. Description Description Harga Harga
A A Photo Transistor Photo Transistor $0.70 $0.55$0.70 $0.55 A A Photo Transistor Photo Transistor 0.40 0.30 0.40 0.30 B B Photo Transistor Photo Transistor 0.45 0.400.45 0.40 C C Photo Transistor Photo Transistor 0.40 0.300.40 0.30 A A Photo Diode Photo Diode 0.75 0.650.75 0.65 A A Photo Diode Photo Diode 0.50 0.400.50 0.40 H H Photo Diode Photo Diode 0.50 0.400.50 0.40 D D Photo Darlington/Motorola Photo Darlington/Motorola 2.95 2.502.95 2.50 D D Photo Darlington Photo Darlington 2.25 1.952.25 1.95 D D Photo Transistor GE Photo Transistor GE 1.85 1.651.85 1.65 D D Photo Transistor GE Photo Transistor GE 1.85 1.651.85 1.65 E E Photo Diode Photo Diode 1.20 0.901.20 0.90 D D Photo Transistor/Motorola Photo Transistor/Motorola 1.90 1.601.90 1.60 F F Photo Darlington Photo Darlington 2.50 1.952.50 1.95 F F Photo Diode Photo Diode 1.60 1.401.60 1.40 G G Solar Cell Solar Cell 2.10 1.952.10 1.95
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FOTODIODA INFRA MERAHFOTODIODA INFRA MERAH
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FOTODIODA InGaAsFOTODIODA InGaAs
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FOTODIODA ULTRAVIOLETFOTODIODA ULTRAVIOLET
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photodiodeThe photodiode is used to vary current by the amount of light that strikes it. It is placed in the circuit in reverse bias. As with most diodes when in reverse bias, no current flows when in reverse bias, but when light strikes the exposed junction through a tiny window, reverse current increases proportional to light intensity.
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Fundamentals of photodiodeFundamentals of photodiode
Illuminate the pn Illuminate the pn junctionjunction
Electrons and holes Electrons and holes are generated by an are generated by an excitation across the excitation across the gapgap
Generated electrons Generated electrons and holes are and holes are separated and drift to separated and drift to electrodes by electrodes by diffusion potential diffusion potential
ｐ -type ｎ -type
Depletion layer
++++
----
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PENGIRIM DAN PENERIMAPENGIRIM DAN PENERIMA
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LIGHT DETECTOR CIRCUITLIGHT DETECTOR CIRCUIT
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Symbols for Special DiodesSymbols for Special Diodes
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Silicon diodes can be checked for Silicon diodes can be checked for opens and opens and shortsshorts by measuring their resistance with a by measuring their resistance with a DMM or a VOMDMM or a VOM
Zener diodes are checked by measuring Zener diodes are checked by measuring their voltage either their voltage either in-circuit or in a testin-circuit or in a test fixture.fixture.
LEDs can be checked LEDs can be checked out of circuitout of circuit with a with a DC voltage source and a resistor. Put 10 to DC voltage source and a resistor. Put 10 to 20 milliamps through the LED and see if it 20 milliamps through the LED and see if it lights.lights.
Other special diode require special test Other special diode require special test fixtures, such as an fixtures, such as an oscillatoroscillator circuit and circuit and frequency counter for a varactor.frequency counter for a varactor.
TroubleshootingTroubleshooting
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SummarySummary
The zener diode operates in reverse breakdown.
A zener diode maintains a nearly constant voltage across it’s terminals over a specified range of currents. Line regulation is the maintenance of a specific voltage with changing input voltages. Load regulation is the maintenance of a specific voltage for different loads. There are other diode types used for specific RF purposes such as varactor diodes (variable capacitance), Schottky diodes (high speed switching), and PIN diodes (microwave attenuation and switching).
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SummarySummary
Light emitting diodes (LED) emit either infrared or visible light when forward biased.
Photodiodes exhibit an increase in reverse current with light intensity.
The laser diode emits a monochromatic light
