TE-UGM Jurusan Teknik Elektro UGM2007 SPECIAL DIODES Bahan Kuliah minggu ke 5 Elektronika Dasar

TE-UGM Zener 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

TE-UGM ZENER CHARACTERISTIC A 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

TE-UGM Some important characteristics: Nominal Zener Voltage : 5.1V zener, 12V zener, etc. Nominal Bias Current: the I z to get the nominal V z 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 1 O C Dynamic Resistance (Rd): Rd =  V/  I

TE-UGM Zener 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

TE-UGM Basic Zener Circuit Key points: V > V V in > V z I = (V in – V z )/R s  I L +I Z I T = (V in – V z )/R s  I L +I Z ITIT IZIZ ILIL

TE-UGM Calculation: Find R Suppose a 5.1 Volt zener is connected to a 12 Volt supply through a resistor. The zener requires a 15 mA bias, and the load is 510 Ohms. Find the required resistor value. load current: I L = 5.1V / 510  = 10 mA load current: I L = 5.1V / 510  = 10 mA total current: I T = I L + I Z = ( ) = 25 mA total current: I T = I L + I Z = ( ) = 25 mA drop across R: V R = 12V – 5.1V = 6.9 V drop across R: V R = 12V – 5.1V = 6.9 V R value : R = V R / I T = 6.9 V / 25 mA = 276 Ohms R value : R = V R / I T = 6.9 V / 25 mA = 276 Ohms Select standard value resistor: R = 270 Ohms Select standard value resistor: R = 270 Ohms

TE-UGM DATA SHEET

TE-UGM Zener Diode Applications Regulation In this simple illustration of zener regulation circuit, the zener diode will “adjust” it’s impedance based on varying input voltages and loads (R L ) 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.

TE-UGM A 10 V zener has 20 mA of bias current. The load resistor across the zener is 20 Ohms. What power rating should the zener have? Remember: if the load is removed, all current is in the zener. A 10 V zener has 20 mA of bias current. The load resistor across the zener is 20 Ohms. What power rating should the zener have? Remember: if the load is removed, all current is in the zener. Find total current: Find total current: I= I + I = 20mA + 50mA = 70 mAI T = I BIAS + I LOAD = 20mA + 50mA = 70 mA Find power in zener (Pz) at a current (Iz) = 70 mA: Find power in zener (Pz) at a current (Iz) = 70 mA: P= V I = 10V  70ma = 700 mWP z = V z  I z = 10V  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 PMAX

TE-UGM Troubleshooting Although 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.

TE-UGM Zener Limiting Zener diodes can be used as limiters. The difference to consider for a zener limiter is a it’s zener breakdown characteristics.

TE-UGM Voltage Surge Protectors Fast, high-voltage transients, called “spikes”, on AC power lines can damage electronic equipment. Fast, high-voltage transients, called “spikes”, on 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.

TE-UGM Varactor Diodes A reverse-biased PN junction makes a voltage-controlled capacitor

TE-UGM Fig 3.12 Capacitance range: from 50 pF to 500 pF Varactor Capacitance

TE-UGM Varactor 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.

TE-UGM Calculation: C & fR If the varactor of figure 3.12 is biased at VR =5 V. If the varactor of figure 3.12 is biased at VR =5 V. 1.Find the capacitance from the graph. 2.Find the resonant frequency with a 253 uH inductor. From the graph, C = 100 pF. From the graph, C = 100 pF. Resonant frequency f = 1/(2LC) = 1.0 MHz Resonant frequency f R = 1/(2LC) = 1.0 MHz

TE-UGM Varactor Tuner Similar tuners are used in TVs, cell-phones, etc.

TE-UGM Varactor Diodes The varactor diode can be useful in filter circuits as the adjustable component.

TE-UGM The PIN Diode Usable at high-frequencies

TE-UGM 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.

TE-UGM Not a PN junction Not a PN junction Fast, but reverse breakdown voltage less than 50 V Fast, but reverse breakdown voltage less than 50 V Schottky Diodes

TE-UGM 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.

TE-UGM 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.

TE-UGM TUNNEL DIODE CHARACTERISTIC The step-recovery diode is also used for fast switching applications.

TE-UGM 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.

TE-UGM Laser is an abbreviation of …... Laser is an abbreviation of …... Light Amplification by Stimulated Emission of Radiation Light Amplification by Stimulated Emission of Radiation “ Stimulated emission ” antonym of “ spontaneous emission ”“ Stimulated emission ” antonym of “ spontaneous emission ” optical transition stimulated by the effect of electric field of light wave on the contrary usually emission occur spontaneously without help of electric fieldoptical transition stimulated by the effect of electric field of light wave on the contrary usually emission occur spontaneously without help of electric field

TE-UGM What is the difference between LED and LD? LED is light emitting diode LED is light emitting diode LD is laser diode LD is laser diode Diode is a semiconductor device which has an effect of rectificationDiode is a semiconductor device which has an effect of rectification Both LED and LD are semiconductor diode with a forward bias. Both emit lightBoth LED and LD are semiconductor diode with a forward bias. Both emit light LED emits light by spontaneous emission mechanism, while LD has an optical cavity which enables multiplication of photon by stimulated emissionLED emits light by spontaneous emission mechanism, while LD has an optical cavity which enables multiplication of photon by stimulated emission

TE-UGM Explain how the light is transmitted through optical fiber. Light is transmitted along the core by total reflection mechanism at the boundary with the cladding layer Light is transmitted along the core by total reflection mechanism at the boundary with the cladding layer N=1.46 N=1.48 cladding core Light Ray Entering Core from Air Light is propagated by Total internal reflection CROSS SECTION

TE-UGM LEDs: Light Emitting Diodes Brightness proportional to current Brightness proportional to current Colors: red, white, blue, green, orange, yellow Colors: red, white, blue, green, orange, yellow Drop across an LED is about 1.5 Volts Drop across an LED is about 1.5 Volts

TE-UGM Optical 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.

TE-UGM How much power does an LED consume if it requires 25 mA and has a forward drop of 2.0 Volts? How much power does an LED consume if it requires 25 mA and has a forward drop of 2.0 Volts? P = V  I = 2V .025A = 50 mW P = V  I = 2V .025A = 50 mW Calculation: Power in an LED

TE-UGM Bright, but consumes a lot of power Bright, but consumes a lot of power Typically multiplexed to conserve power Typically multiplexed to conserve power THE 7-SEGMENT DISPLAY

TE-UGM SEGMENT DISPLAY The seven segment display is an example of LEDs use for display of decimal digits.

TE-UGM How much power would a 4-digit 7- segment LED display consume if each LED required 10 mA and had a forward drop of 1.5 Volts? How much power would a 4-digit 7- segment LED display consume if each LED required 10 mA and had a forward drop of 1.5 Volts? Power in one LED: Power in one LED: P = V  I = 2V .01A = 20 mWP LED = V  I = 2V .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  PLED = 7  20mW = 140 mWPD = 7  PLED = 7  20mW = 140 mW Total Power: Total Power: PT = 4  PD = 4  140 mW = 560 mWPT = 4  PD = 4  140 mW = 560 mW That’s over half a Watt! That’s over half a Watt! Power in a 7-Segment Display

TE-UGM Multiplexing to Reduce Power Suppose a 4-digit display requires 400 mW if all segments are lit. If the display is multiplexed so that each digit is lit in a continuous sequence (1,2,3,4,1,2,3,4...) how much power would the display use? Suppose a 4-digit display requires 400 mW if all segments are lit. If the display is multiplexed so that each digit is lit in a continuous sequence (1,2,3,4,1,2,3,4...) how much power would the display use? Since each digit is on for only 25% of the time, Since each digit is on for only 25% of the time, P = 0.25  400 mW = 100 mW P = 0.25  400 mW = 100 mW

TE-UGM Troubleshooting Although 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.

TE-UGM DIODA FOTO

TE-UGM Fig. Description Harga Fig. Description Harga A Photo Transistor $0.70 $0.55 A Photo Transistor $0.70 $0.55 A Photo Transistor A Photo Transistor B Photo Transistor B Photo Transistor C Photo Transistor C Photo Transistor A Photo Diode A Photo Diode A Photo Diode A Photo Diode H Photo Diode H Photo Diode D Photo Darlington/Motorola D Photo Darlington/Motorola D Photo Darlington D Photo Darlington D Photo Transistor GE D Photo Transistor GE E Photo Diode E Photo Diode D Photo Transistor/Motorola D Photo Transistor/Motorola F Photo Darlington F Photo Darlington F Photo Diode F Photo Diode G Solar Cell G Solar Cell

TE-UGM FOTODIODA INFRA MERAH

TE-UGM FOTODIODA InGaAs

TE-UGM FOTODIODA ULTRAVIOLET

TE-UGM

TE-UGM

TE-UGM

TE-UGM photodiode The 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.

TE-UGM Fundamentals of photodiode Illuminate the pn junction Illuminate the pn junction Electrons and holes are generated by an excitation across the gap Electrons and holes are generated by an excitation across the gap Generated electrons and holes are separated and drift to electrodes by diffusion potential Generated electrons and holes are separated and drift to electrodes by diffusion potential ｐ -type ｎ -type Depletion layer

TE-UGM

TE-UGM

TE-UGM

TE-UGM

TE-UGM

TE-UGM

TE-UGM PENGIRIM DAN PENERIMA

TE-UGM LIGHT DETECTOR CIRCUIT

TE-UGM

TE-UGM

TE-UGM Symbols for Special Diodes

TE-UGM Silicon diodes can be checked for opens and shorts by measuring their resistance with a DMM or a VOM Silicon diodes can be checked for opens and shorts by measuring their resistance with a DMM or a VOM Zener diodes are checked by measuring their voltage either in-circuit or in a test fixture. Zener diodes are checked by measuring their voltage either in-circuit or in a test fixture. LEDs can be checked out of circuit with a DC voltage source and a resistor. Put 10 to 20 milliamps through the LED and see if it lights. LEDs can be checked out of circuit with a DC voltage source and a resistor. Put 10 to 20 milliamps through the LED and see if it lights. Other special diode require special test fixtures, such as an oscillator circuit and frequency counter for a varactor. Other special diode require special test fixtures, such as an oscillator circuit and frequency counter for a varactor. Troubleshooting

TE-UGM Summary  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).

TE-UGM Summary  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