Electronic Devices and Circuits PDF

Electronic Devices and Circuits Electrical Classification 1. Conductors 2. Insulators 3. Semiconductors Insulators A material that does not conduct electrical current under normal conditions Mostly compound materials Valence electrons are tightly bound to the atoms Number of va...

Electronic Devices and Circuits Electrical Classification 1. Conductors 2. Insulators 3. Semiconductors Insulators A material that does not conduct electrical current under normal conditions Mostly compound materials Valence electrons are tightly bound to the atoms Number of valence electrons = 5 to 8 Very high resistivities (ex. Mica = 1012 Ω-cm) Conductors A material that easily conduct current Usually a single-element material (ex. Copper, gold, aluminum) Valence electrons = 1 to 3 Resistivities are very low (ex. Copper = 10-6 Ω-cm) Semiconductors In its pure (intrinsic) state, it is neither a good conductor nor a good insulator Valence electrons = 4 Examples are: Silicon (Si), Germanium (Ge), and Carbon (C) Resistivity 50 Ω-cm (germanium) 50000 Ω-cm (silicon)  Semiconductors Semiconductors are between conductors and insulators in their ability to conduct electricity. Unlike metals, silicon forms strong covalent bonds (shared electrons) with its neighbors. Intrinsic silicon is a poor conductor because most of the electrons are bound in the crystal and take part in forming the bonds between atoms. Floyd, Electronic Devices (9Th Edition)  Periodic Table of Elements Floyd, Electronic Devices (9Th Edition) Energy Gap Comparison Eg = 0.67 eV (Ge) Eg = 1.1 eV (Si) Eg = 1.43 eV (GaAs) Semiconductors In intrinsic silicon, a few electrons can jump the energy gap between the valence and conduction band. Having moved into the conduction band, a “hole” (vacancy) is left in the crystal structure. Floyd, Electronic Devices (9Th Edition) Doping Certain impurities will change the conductivity of silicon. An impurity such as Antimony has an electron that is not part of the bonding electrons so is free. This creates an n-material. The process of adding impurities to the intrinsic semiconductor is known as doping. Doping increases the conductivity of the semiconductor N-Type and P-Type Material Adding atoms that are having five valence electrons (pentavalent) or three valence electrons (trivalent) creates n- type and p-type material, respectively. N-type material means it has most of the current carriers being the electrons therefore the majority carriers are the electrons and the minority carriers are the holes  Semiconductor Current Floyd, Electronic Devices (9Th Edition) The PN Junction A p- and an n-material together form a pn junction. When the junction is formed, conduction electrons move to the p region, and fall into holes. Filling a hole makes a negative ion and leaves behind a positive ion in the n-region. This creates a thin region that is depleted of free charges at the boundary. Floyd, Electronic Devices (9Th Edition) The Junction Diode A diode is a semiconductor device with a single pn junction and metal connections to leads. It has the ability to pass current in only one direction. Floyd, Electronic Devices (9Th Edition) The Junction Diode Malvino, Electronic Principles The Junction Diode Shockley’s Equation: 𝑉𝐷 𝐼𝐷 = 𝐼𝑠 𝑒 𝜂𝑉𝑇 − 1 [𝐴] Is = reverse saturation current VD = applied forward bias voltage across the diode n = ideality factor [1, 2]; default = 1 VT = thermal voltage Floyd, Electronic Devices (9Th Edition) The Junction Diode Thermal Voltage 𝑘𝑇 𝑉𝑇 = 𝑞 k = Boltzmann’s Constant = (1.38 x 10-23 J/K) T = absolute temperature in Kelvins q = magnitude of elementary charge = 1.6 x 10-19 C Floyd, Electronic Devices (9Th Edition) Temperature Effects on Is and VTH 𝐼𝑆1 = 𝐼𝑆 𝑒 𝑘 𝑇1 −𝑇𝑜 IS = saturation current at room temperature IS1 = saturation current at new temperature k = 0.07/oC T1 = new temperature To = room temperature Floyd, Electronic Devices (9Th Edition) Temperature Effects on Is and VTH 𝑉𝑇𝐻1 = 𝑉𝑇𝐻 + 𝑘(𝑇1 − 𝑇𝑜 ) VTH1 = threshold voltage at new temperature VTH = threshold voltage at room temperature k = -2.5 mV/oC for Ge, -2.0 mV/oC for Si T1 = new temperature To = room temperature Floyd, Electronic Devices (9Th Edition) Diode Models There are three models of a diode that may be used in circuit analysis: 1. Ideal 2. Practical 3. Complete Ideal Diode Model The ideal model of a diode is the least accurate approximation and can be represented by a simple switch Floyd, Electronic Devices (9Th Edition) Practical Diode Model The practical model includes the barrier potential. Floyd, Electronic Devices (9Th Edition) Complete Diode Model The complete model of a diode is the most accurate approximation and includes the barrier potential, the small forward dynamic resistance (r’d) and the large internal reverse resistance (r’R) Floyd, Electronic Devices (9Th Edition) Resistance Levels DC or Static Resistance The application of a dc voltage to a circuit containing a semiconductor diode will result in an operating point on the characteristic curve that will not change with time. 𝑉𝐷 𝑅𝐷 = 𝐼𝐷 Resistance Levels AC or Dynamic Resistance The application of a dc voltage to a circuit containing a semiconductor diode will result in an operating point on the characteristic curve that will not change with time. Δ𝑉𝑑 26 𝑚𝑉 𝑟𝑑 = = Δ𝐼𝑑 𝐼𝐷 Resistance Levels AC or Dynamic Resistance Considering the resistance of the connection of the semiconductor and the external metallic conductor (called contact resistance) and the semiconductor itself (body resistance) 26 𝑚𝑉 𝑟𝑑 = + rB 𝐼𝐷 Diode Capacitances Transition Capacitance predominant capacitive effect in the reverse-bias region 𝐶(0) 𝐶𝑇 = 𝑉𝑅 𝑛 1+ 𝑉𝐾 Diode Capacitances Diffusion Capacitance predominant capacitive effect in the forward-bias region 𝜏 𝐶𝐷 = 𝐼𝐷 𝑉𝐾 Boylestad, Electronic Circuit and Devices Theory Reverse Recovery Time 𝑡𝑟𝑟 = 𝑡𝑠𝑡𝑜𝑟𝑎𝑔𝑒 + 𝑡𝑡𝑟𝑎𝑛𝑠𝑖𝑡𝑖𝑜𝑛 Boylestad, Electronic Circuit and Devices Theory Zener Diodes The zener diode is designed to operate in the reverse breakdown region. Ideally, the reverse breakdown has a constant breakdown voltage. This makes it useful as a voltage reference, which is its primary application. Floyd, Electronic Devices (9Th Edition) Zener Diodes The zener impedance, ZZ, is the ratio of a change in voltage in the breakdown region to the corresponding change in current: Δ𝑉𝑍 𝑍𝑍 = Δ𝐼𝑍 Zener Diodes The temperature coefficient of a zener diode can be specified as the percent change in zener voltage for each degree Celsius change in temperature: Δ𝑉𝑍 𝑉𝑍 % 𝑇𝐶 = Δ𝑇 𝐶 Δ𝑉𝑍 𝑚𝑉 𝑇𝐶 = Δ𝑇 𝐶 Varactor Diodes A varactor diode is a special purpose diode operated in reverse- bias to form a voltage-controlled capacitor. The width of the depletion region increases with reverse-bias. Floyd, Electronic Devices (9Th Edition) Optical Diodes Diodes can be made to emit light (electroluminescence) or sense light. Light-emitting diodes (LEDs) vary widely in size and brightness – from small indicating lights and displays to high- intensity LEDs that are used in traffic signals, outdoor signs, and general illumination. Photodiodes A photodiode is a special light sensitive diode with a clear window to the pn junction. It is operated with reverse bias. Reverse current increases with greater incident light. Floyd, Electronic Devices (9Th Edition) LASER Diodes A laser diode converts an electrical signal into coherent (monochromatic) light. It produces an intense narrow beam of light from the recombination of electrons and holes in the depletion region. Floyd, Electronic Devices (9Th Edition) Schottky Diode A Schottky diode is a metal-to-semiconductor contact diode that is used primarily in high frequency and fast-switching applications. It has a low forward voltage drop and high efficiency but rather low reverse voltage rating. Floyd, Electronic Devices (9Th Edition) PIN Diode A PIN diode is a three layer diode consisting of a p and n layers separated by a narrow intrinsic layer. In microwave applications, the pin diode acts as a voltage-controlled resistor. Certain types are used as photodetectors in fiber optic systems. Floyd, Electronic Devices (9Th Edition) Tunnel Diode A tunnel diode has a characteristic curve that shows a negative resistance reading between B and C with a small forward voltage. The negative resistance region is unstable. Taking advantage of this characteristic, the tunnel diode can be used in an oscillator circuit at microwave frequencies. Floyd, Electronic Devices (9Th Edition) DC Power Supply Transformer It is a static device that transfers electrical energy from the primary winding without affecting the frequency. Transformer For an ideal transformer: 𝑃𝑃 = 𝑃𝑠 𝑁𝑠 Turns Ratio: 𝑎= 𝑁𝑝 𝑉𝑠 𝑁𝑠 Voltage Ratio: = 𝑉𝑝 𝑁𝑝 2 𝑍𝑠 𝑁𝑠 Impedance Ratio: = 𝑍𝑝 𝑁𝑝 𝐼𝑠 𝑁𝑝 Current Ratio: = 𝐼𝑝 𝑁𝑠 Rectifier Circuits It is a device used to change the ac input voltage to a pulsating dc. Re: Rectifier Circuits Half-wave Rectifier Full-wave Bridge-type Rectifier Full-wave Center-tapped Rectifier Half-Wave Rectifier HWR Operation HWR Operation HWR Operation Average Value of HWR 𝒂𝒓𝒆𝒂 𝒂𝒗𝒆𝒓𝒂𝒈𝒆 𝒗𝒂𝒍𝒖𝒆 = 𝒑𝒆𝒓𝒊𝒐𝒅 𝒃 ‫𝒇 𝒂׬‬ 𝒕 𝒅𝒕 𝒂𝒗𝒆𝒓𝒂𝒈𝒆 𝒗𝒂𝒍𝒖𝒆 = 𝒃−𝒂 Average Value of HWR 𝑽𝒑 𝑽𝑨𝑽𝑬 = ≈ 𝟎. 𝟑𝟏𝟖𝑽𝒑 𝝅 where: Vp = peak value of the voltage Frequency of HWR Signal The output frequency of the HWR is just equal to the input frequency. 𝒇𝒐𝒖𝒕 = 𝒇𝒊𝒏 Effects of Barrier Potential (HWR) 𝑽𝒑 𝒐𝒖𝒕 = 𝑽𝒑(𝒊𝒏) − 𝟎. 𝟕𝑽 Peak Inverse Voltage (HWR) The peak inverse voltage (PIV) is equal to the peak value of the input voltage, and the diode must be capable of withstanding this amount of repetitive reverse voltage. A diode should be rated at least 20% higher than the PIV. 𝑷𝑰𝑽 = 𝑽𝒑(𝒊𝒏) Full-Wave Rectifier Average Value of FWR 𝟐𝑽𝒑 𝑽𝑨𝑽𝑬 = ≈ 𝟎. 𝟔𝟑𝟔𝑽𝒑 𝝅 where: Vp = peak value of the voltage Frequency of FWR Signal The output frequency of the FWR is equal to twice of input frequency. 𝒇𝒐𝒖𝒕 = 𝟐𝒇𝒊𝒏  Center-Tapped FWR Operation A center-tapped rectifier is a type of full-wave rectifier that uses two diodes connected to the secondary of a center- tapped transformer, as shown in given figure. Center-Tapped FWR Operation Center-Tapped FWR Operation Center-Tapped FWR Operation Effect of the Turns Ratio on Output Voltage Effect of the Turns Ratio on Output Voltage Effect of the Turns Ratio on Output Voltage In any case, the output voltage is given by the following equation, no matter what the turns ratio is. 𝑽𝒑(𝒔𝒆𝒄) 𝑽𝒐𝒖𝒕 = − 𝟎. 𝟕𝑽 𝟐 Peak Inverse Voltage (CTFWR) Each diode in the FWR is alternately put in forward and reverse bias. 𝑷𝑰𝑽 = 𝑽𝒑(𝒔𝒆𝒄) − 𝟎. 𝟕 𝑷𝑰𝑽 = 𝟐𝑽𝒑(𝒐𝒖𝒕) + 𝟎. 𝟕 Bridge FWR Operation Bridge FWR Operation Bridge FWR Output Voltage Neglecting the diode drops, 𝑽𝒐𝒖𝒕 = 𝑽𝒑(𝒔𝒆𝒄) Since that a bridge circuit would always involve two diodes in series and taking the drops into account, 𝑽𝒐𝒖𝒕 = 𝑽𝒑(𝒔𝒆𝒄) − 𝟏. 𝟒𝑽  Peak Inverse Voltage (BFWR) If we neglect the diode drops, the PIV would be: 𝑷𝑰𝑽 = 𝑽𝒑(𝒔𝒆𝒄) = 𝑽𝒑(𝒐𝒖𝒕) Not neglecting the diode drops: 𝑷𝑰𝑽 = 𝑽𝒑(𝒐𝒖𝒕) + 𝟎. 𝟕 Summary Ripple Voltage It is an AC voltage that indicates the magnitude of the rms ripple voltage at the output of a filter circuit. Ripple Factor It is an indication of the effectiveness of the filter and is defined as: 𝑎𝑐 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑟= 𝑥100% 𝑑𝑐 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑟𝑖𝑝𝑝𝑙𝑒 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉𝑟𝑚𝑠 ) 𝑟= 𝑥100% 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝑑𝑐 𝑣𝑜𝑙𝑡𝑎𝑔𝑒(𝑉𝑑𝑐 𝑜𝑟 𝑉𝑎𝑣𝑒 ) Ripple Factor 𝑽𝒓 𝒓𝒎𝒔 = 𝑽𝟐𝒐,𝒓𝒎𝒔 − 𝑽𝟐𝑫𝑪 𝟏 𝑽𝒓 𝒑𝒑 ≅ 𝑽𝒑 𝒓𝒆𝒄𝒕 𝒇𝑹𝑳 𝑪 𝟏 𝑽𝑫𝑪 ≅ 𝟏 − 𝑽𝒑 𝒓𝒆𝒄𝒕 𝟐𝒇𝑹𝑳 𝑪 Filters Filters It is used to keep the ripple component from appearing in the output. It is designed to convert pulsating DC from rectifier circuits into a suitably smooth dc level. Two basic types of power supply filters: 1. Capacitance filter (C-filter) 2. RC filter Filters Filters  C-Filters It is the simplest and most economical filter available. C-Filters 𝐼𝑑𝑐 2.4𝐼𝑑𝑐 2.4𝑉𝑑𝑐 𝑉𝑟(𝑟𝑚𝑠) = = = 4 3𝑓𝐶 𝐶 𝑅𝐿 𝐶 𝐼𝑑𝑐 4.17𝐼𝑑𝑐 𝑉𝑑𝑐 = 𝑉𝑚 − = 𝑉𝑚 − 4𝑓𝐶 𝐶 𝑉𝑟(𝑟𝑚𝑠) 2.4𝐼𝑑𝑐 2.4 𝑟= 𝑥100% = × 100% = × 100% 𝑉𝑑𝑐 𝐶𝑉𝑑𝑐 𝑅𝐿 𝐶 RC-Filters It is used to further reduce the amount of ripple voltage across a capacitor filter. Its primary objective is to pass most of the dc component while attenuating or reducing as much of the ac component as possible. RC-Filters RC-Filters (DC Operation) Both C1 and C2 are opened 𝑅𝐿 𝑉′𝑑𝑐 = 𝑉𝑑𝑐 𝑅𝐿 + 𝑅 RC-Filters (AC Operation) For a full-wave rectifier with ac ripple at 120 Hz, the impedance of a capacitor can be calculated using 1.3 𝑋𝑐 = 𝐶 𝑋𝑐 𝑉′𝑟(𝑟𝑚𝑠) = 𝑉𝑟(𝑟𝑚𝑠) 𝑅 Bleeder Resistors Voltage Regulator A voltage regulator can furnish nearly constant output with excellent ripple rejection. Line Regulation Specifies how much the dc output changes for a given change in regulator’s input voltage. Δ𝑉𝑜𝑢𝑡 𝐿𝑖𝑛𝑒 𝑅𝑒𝑔𝑢𝑙𝑎𝑡𝑖𝑜𝑛 = × 100% Δ𝑉𝑖𝑛 Load Regulation Specifies how much change occurs in the output voltage for a given range of load current values, usually from no load (NL) to full load (FL). 𝑉𝑁𝐿 − 𝑉𝐹𝐿 𝐿𝑅 = × 100% 𝑉𝐹𝐿 IC Voltage Regulators IC Voltage Regulators IC Voltage Regulators Adjustable Voltage Regulators The adjustable voltage regulator allows the user to set the output voltage to a desired regulated value. Adjustable Voltage Regulators R1 and R2 set the output to any desired voltage over the adjustment range (1.2 to 3.7 V). The output voltage can be computed as: 𝑅2 𝑉𝑜 = 𝑉𝑟𝑒𝑓 1+ + 𝐼𝑎𝑑𝑗 (𝑅2 ) 𝑅1 Note that typical IC values are: 𝑉𝑟𝑒𝑓 = 1.25 𝑉, 𝐼𝑎𝑑𝑗 = 100 µ𝐴 Zener Diodes as Voltage Regulators A Zener diode is a silicon pn junction device that is designed for operation in the reverse-breakdown region. Zener Breakdown occurs in a Zener diode at low reverse voltages (≤ 5𝑉). Avalanche Breakdown occurs in a Zener diode at high reverse voltages (>5V) Sample Problems  Question 1 Find I, V1, V2, and Vo.  Question 2 Determine Vo for the network shown:  Question 3 Determine the value of ID and VO.  Question 4 Determine ID1. Question 5  Question 6 Line voltage may be from 105 Vrms to 125 Vrms in a half- wave rectifier. With a 5:1 step-down transformer, the maximum peak load voltage is closest to  Question 7 What is the peak load voltage out of a bridge rectifier for a secondary voltage of 10 Vrms?  Question 8 A full-wave rectified signal of 18 Vp is connected to a 400 uF filter capacitor. What is the ripple factor at a load of 100 mA?  Question 9 A half-wave rectifier has a load resistance of 3.5 kilo-ohm. If the diode and secondary of the transformer have a total resistance of 800 ohm and the ac input voltage has 240 V (peak value), determine the DC power output.  Question 10 Determine the regulated voltage of a typical LM317 IC Adjustable Voltage Regulator circuit with R1 = 250 ohms and R2 = 2 kohms. References S. Cuervo, ECE Handbook: Electronics Engineering Villamor, GuideBook in Electronics Engineering A. Hambley, Electrical Engineering : Principles and Applications