Download ET 238B - Diodes

Device Peripherals ET 238B
Introduction
Overview
• Items to be covered
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Syllabus Review
Lab Safety
The PN Junction
Diodes
Transistors
OP-Amps
Purpose of the course
• An intermediate course
• Covers the design, theory and operation of electronic slot
machines, casino management systems, player tracking
systems, linked machines, local and wide area
progressive systems.
• Students will implement their design of an electronic slot machine
• Who should take the course
• Slot Technology students at CSN , Slot attendants in casinos and
those that want to be slot Technicians that have a analog and digital
electronics, employees of slot machine manufacturers, Etc.
• Outcomes
• Per syllabus
Purpose of the course
• Syllabus Review
• Contact Information
• Grading
• Weekly Topics and Schedule
Lab Safety
• Precautions when working on slot
machines – Appendix C handout
• Remove all metal objects to reduce the
possibility of electrical shock
• Don’t make contact between voltages on
wires and other objects – including yourself
• Power should be turned off adding/removing
electronic components
• Helps prevent shocks and equipment damage
Lab Safety
• Precautions when working on slot
machines – Continued
•
Disconnect machine before changing operating
voltage/frequency settings
• 110 V - 220V operation
• 50 or 60Hz operation
• Hopper containing coins can be very heavy
• Handle all glass and sheet metal carefully
• Ensure all used electrical outlets are correctly wired
ET 238B - PN Junction
• Atomic Structure
• Characteristics
• Smallest particle of an element - anything smaller is the
element
• Bohr Model Reference
• Atomic Number
• Equals the number of protons and the normal number of
electrons
• Determines location on Periodic Table Reference
• Electron Shells and Orbits
• Electrons closer to nucleus have lower energy than those
further away
ET 238B - PN Junction
• Atomic Structure
• Electron Shells and Orbits
• Energy Levels
• Electrons aren’t randomly dispersed
• They are in different Shells (orbits)
• Electrons in the same orbit have the same or nearly the
same levels of energy
• Reference Image
• Number of electrons in each shell
• Ne = 2n2, n = the shell number, (k = 1, L = 2, etc.)
• Starts with Shell 1 closest to the nucleus
• Valence Electrons
• In outermost shell have the highest energy and are less tightly
bound to the atom than closer electrons
• Key to chemical and electrical properties of the element
Image from: http://superstem.org/newsite/EELS.htm
ET 238B - PN Junction
• Atomic Structure
• Electron Shells and Orbits
• Ionization
• The protons and electrons have equal and opposite charges
• Protons are + Electrons are • When an atom absorbs energy the energy levels of electrons is
raised
• If the energy rise is large enough the electrons can chan
levels
• The necessary step is lowest for the electrons in the outer
shell, the Valence Shell
• If an electron gains enough energy to leave the valence
shell - It is a free electron.
• If an atom loses an electron I has a positive charge - if it gains
an electron it has a negative charge
ET 238B - PN Junction
• Semiconductors, Conductors & Insulators
• Conductors
• Characteristics
• Easily conducts electricity (also heat)
• Examples of better conductors
• Copper
• Silver
• Gold
• Aluminum
• Energy Gap
• Small gap between Valence level and conduction level (free
electrons) -- See Figure 1-5c on page 6
• See the Diagram of a copper atom Figure 1-6b on page 7
• Insulators
• Characteristics
• Materials that don’t usually conduct electric current
ET 238B - PN Junction
• Semiconductors, Conductors & Insulators
• Insulators
• Characteristics
• Examples
• Usually compounds not elements
• e.g. rubber, paper, plastics
• Energy Gap
• Has the largest gap
• Semiconductors
• Characteristics
• Not a good conductor or insulator
• Examples
• Silicon
• Germanium
ET 238B - PN Junction
• Semiconductors, Conductors & Insulators
• Semiconductors
• Characteristics
• Examples
• carbon
• compounds, e.g., gallium arsenide
• Single element semiconductors all have four Valence Electrons
• Energy Gap
• Medium size gap between Valence level and conduction level
(free electrons) -- See Figure 1-5b on page 6
• See the Diagram of a silicon atom Figure 1-6a on page 7
• Silicon vs Germanium
• See Reference Diagrams of both
• Reference
ET 238B - PN Junction
• Semiconductors, Conductors & Insulators
• Silicon vs Germanium
• Reference (continued)
• The valence shell for silicon is closer than the one for
germanium
• Third shell for silicon and fourth for germanium
• Germanium requires less energy to free valence electrons
than silicon - thus lower threshold voltages
• Silicon devices are more stable at high operating temps
• Heat will cause less free electrons than in germanium devices
• Covalent Bonds
• Both Silicon and Germanium crystals use covalent
bonding - If they are pure.
• See diagram for Silicon - Reference
ET 238B - PN Junction
• Covalent Bonds
• Characteristics
• Shares a valence electron with each of the neighboring
silicon atoms
• Stabilizes the crystal structure
• Conduction in Semiconductors
• Characteristics
• Semiconductors always have electrons in the conduction
band (free) at a temperature of absolute zero with no other
external excitation
• Conduction Electrons and holes
• At room temperature an intrinsic silicon crystal
• Has a number of free electrons called conduction electrons
• Has a number of electron holes
ET 238B - PN Junction
• Conduction in Semiconductors
• Conduction Electrons and holes
• At room temperature an intrinsic silicon crystal
• Recombination is when a free electron losses energy and fills a
hole
• The creation of electron-hole pairs and recombination occurs
randomly in an unexcited crystal
• Electron and hole current
• Characteristics
• When an electric potential is placed across the silicon crystal
• Electron and apparent hole movement isn’t random
• Electron flow -Electron Current
• The Positive potential of the applied voltage attracts the
thermally generated free electrons
• Happens in the conduction band
ET 238B - PN Junction
• Conduction in Semiconductors
• Electron and hole current
• Hole flow - Hole Current
• Happens in the Valence band
• Electrons in the valence band with out enough energy
cannot leave the valence band
• However they can move through the valence band of the
crystal structure and get closer to the external - charge
• N-Type & P-Type Semiconductors
• Characteristics
• Conductivity of silicon and germanium can be drastically
increased by adding impurities
• Called Doping
• Used to increase either the number of holes or electrons
• Two types of impurities N and P
ET 238B - PN Junction
• N-Type & P-Type Semiconductors
• N-Type Semiconductors
• N stands for the negative charge on an electron
• Impurities with five valence electrons are added
• e.g. arsenic (As), phosphorus (P), bismuth(Bi), antimony (Sb)
• The impurity integrates into of covalent bonded crystal
• The fifth electron in its valence band becomes a free electron
• Electrons are the majority carriers and carry more charge
• P-Type Semiconductors
• P stands for the positive charge on an atom in the crystal
• Impurities with three valence electrons are added
• e.g., boron (B), indium (In), gallium (Ga)
• The impurity integrates into of covalent bonded crystal
• The lack of a fourth valence electron results in a hole
• Holes are the majority carriers and carry more charge
ET 238B - Diodes
• Diode
• Characteristics
• Part of the same crystal is doped with P-Type material and
part with N-Type
• A junction is formed where the materials meet
• There is no charge on either the N or P regions
• Number of electrons equals the number of protons
• Depletion Region Formation
• Before the junction between the “n & p” regions is formed
both regions have zero net charge
• Just as the junction is formed
• The n regions losses free electrons to the p region
• Leaves holes and a net positive charge
• The newly arrived electrons combine with p region holes
• Leaves a net negative charge
ET 238B - Diodes
• Diode
• Depletion Region Formation
• The net negative and positive charged areas are free of
charge carriers >>> Depletion region
• The depletion region grows until the negative charge on the ptype side repels any further electrons crossing the junction
• Barrier Potential
• Measure of the voltage potential across the depletion region in
volts
• The net positive and negative charges on both sides of the
junction create an electronic field
• Forward Bias
• Condition that allows significant current through a diode
• Requirements
• VBIAS > Barrier potential
ET 238B - Diodes
• Biasing the Diode
• Forward Bias
• Requirements
• VBIAS + is connected to the P material and VBIAS - is connected to
the N region
• Process
• After the electrons from the N region enter the P region they
have lost energy and inter a available hole
• Those electrons are then in the Valence Band
• The electrons then move through the common valence band to
the positive charge applied to the P region
• Effectively the holes flow towards the junction
• Reverse Bias
• Condition that prevents significant current through a diode
• Requirements
• + of the reverse bias voltage is connected to the N region
ET 238B - Diodes
• Biasing the Diode
• Reverse Bias
• Requirements
• - of the reverse bias voltage is connected to the P region
• Initial Currents
• Reverse voltage is applied then:
• Electrons flow in the N region to the attached + potential
• Holes flow to the attached - potential
• Depletion region grows
• The resulting initial rush of current quickly decreases
• Reverse Current
• Flows due to minority carriers in N and P regions
• Holes and electrons
• Carries are thermally generated electrons and at a higher
energy level than the conduction band of the N region
• Thus they can easily transition to the N region & fill a Hole
ET 238B - Diodes
• Biasing the Diode
• Reverse Bias
• Reverse Breakdown
• Occurs when the applied reverse bias voltage is to large
• Results in an avalanche current
• These high currents can cause heat damage to a diode
ET 238B - Diodes
Copied from: http://en.wikipedia.org/wiki/Image:Rectifier_vi_curve.GIF
ET 238B - Diodes
• V-I Characteristics of Diodes
• Forward Bias
• See V-I curve on the previous slide
• At any point along the curve you can take Voltage/Current
values to calculate the dynamic (aka AC resistance) resistance
(r’d) of the diode
• Knee voltage
• Nominally 0.6 to 0.7V for silicon
• Nominally 0.2 to 0.3 V for germanium
• red light-emitting diodes (LEDs) can be 1.4 V or more and
blue LEDs can be up to 4.0 V.
• Reverse Bias
• See V-I curve on the previous slide
• The knee voltage is the reverse breakdown voltage (VBR)
• Found in Manufacture’s specifications
• Above VBR the current rapidly increases
ET 238B - Diodes
• V-I Characteristics of Diodes
• Temperature Effects on V-I Characteristics
• Forward Biased
• As the temperature rises the energy level of the electron in the
N region rises a lower Forward Bias voltage is required
• Reverse Biased
• The reverse current increases, but still is very small
• Diode Models
• Structure and Symbol
• Symbol
• Conventional current
follows with the implied diode arrow
• Electron current flow is against the arrow
• P region is known as the Anode and the Cathode is on the N
region side of the pn-junction
ET 238B - Diodes
• Diode Models
• Structure and Symbol
• Electron current flow is against the arrow
• P region is known as the Anode and the Cathode is on the N
region side of the pn-junction
ET 238B - Diodes
• Major uses for Diodes
• Basic DC Power Supply
• Half-Wave Rectifiers
• Full-Wave Rectifiers
• Power Supply Filters and Regulators
• Diode Limiting and Clamping Circuits
• Voltage Multipliers
ET 238B - Diodes
• Zener Diodes
• Characteristics
• Major application - providing a constant reference voltage for
voltage regulators
• Zeners maintain near constant DC voltages under proper
conditions
• Designed to operate in the reverse break-breakdown region
• Zener Breakdown
• Two types of break down are used by Zener Diodes
• avalanche breakdown
• Usually have a breakdown voltage of over 5 volts
• zener breakdown
• Usually have a breakdown voltage of 5 or less volts
ET 238B - Diodes
• Zener Diodes
• Zener Breakdown
• Voltage Ranges
• Commercially available voltages range from 1.8 to 200V
• Tolerances range from 1% to 20%
• Breakdown Characteristics
• As VR (the reverse Voltage) increases very little current flows
until the knee of the curve is reached
• Knee known as the Zener Voltage
• As Current increases the Zener Voltage VZ slowly increases
• Remains very close to the VZ
• Zener Regulation
• Zener diode current must be at least = to the zener knee (IZK)
current to maintain the constant voltage across it
• Currents greater than the maximum rating (IZM)will damage the
diode
ET 238B - Transistors
• Transistor Structure
• Major Components
• Three Doped Semiconductor Regions
• Either a p-type region between two n-type regions (npn)
• Or a n-type region between two p-type regions (pnp)
• Separated by two pn junctions
• Basic Transistor Operation
• Must be biased to operate as an amplifier
• Usually DC biases that are necessary for AC amplification
ReverseVoltage
ReverseVoltage
Some images from
“The Electronics
Club Web site
Forward Voltage
Forward Voltage
ET 238B - Transistors
• Basic Transistor Operation
• Must be biased to operate as an amplifier
• Usually DC biases that are necessary for AC amplification
• For both types the BE junction is forward biased
• The CB junction is reverses biased
• Currents
• Conventional current flow is assumed.
• Emitter-Base Junction
• The junction has a forward voltage applied across the PN or
NP junction
• PNP
• Positive voltage applied to the P Emitter and the negative side
of the voltage to the N Base
ET 238B - Transistors
• Currents
• Emitter-Base Junction
• PNP
• Positive voltage applied to the P Base and the negative side of
the voltage to the N Emitter
• Collector Base Junction
• Major function of the junction is to remove chares from the
Base
• To function the junction must be reversed biased
• PNP Biasing
• The P Collector is connected to the negative side of the reverse
voltage and the positive side is connected to the N Base.
• NPN Biasing
• The N Collector is connected to the positive side of the reverse
voltage and the negative side is connected to the P Base.
ET 238B - Transistors
• Transistor action
• Three factors for the Collector current to be
controlled by the Base Emitter current
• The emitter needs heavy doping to supply free electrons
• The base only has light doping and is very thin
• The collector voltage is relatively high
• Usually 98% to 99% of the charges supplied by the
Emitter to the Base provide the collector current
• The remaining 1% to 2% provide the Base current
• Electrode Currents
• IEmitter = IBase + ICollector  IE = IB + IC
• Base current controls Collector current
• This is the reason transistors can amplify signals
ET 238B - Transistors
• Base current controls Collector current
• Walk through
• Increased Forward voltage on Base Emitter junction causes
more base current
• More Base current means more majority carriers are in the
Base region to be injected into the collector
• Thus more base current yields more Collector current
• Note the Collector currents are usually between 50 to 100
times the Base currents
Image from Biplolar
Junction Transistor
Theory by Chuck
McManis
http://www.mcmanis.com
/chuck/
ET 238B - Transistors
• Typical Amplifier configurations
• Common Emitter
Image from Thomas L. Floyd
Electronic Devices, 6e and
Electronic Devices: Electron Flow
Version, 4e
ET 238B - Transistors
• Typical Amplifier configurations
• Common Collector
• Used to supply larger loads with current
Image from Thomas L. Floyd
Electronic Devices, 6e and
Electronic Devices: Electron Flow
Version, 4e
ET 238B - Transistors
• Typical Amplifier configurations
• Common Base
• Characteristics
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Provides High Voltage Gain and no phase shift
Maximum Current Gain - 1
Low Input Impedance
Input applied to Emitter Circuit
Image from Thomas L. Floyd
Electronic Devices, 6e and
Electronic Devices: Electron Flow
Version, 4e
ET 238B – OP-Amps
• Integrated Circuit Operation Amplifiers
• OP-Amps for short
• OP Amp Development
• Originally contained only bipolar transistors
• Many OP-Amps have Junction field-effect transistors
inputs
• Draw extremely small currents compared to bipolar
• Many have complementary MOS output transistors
on outputs
• Output voltages can reach within millivolts of the supply
voltages
• Called BiMOS
• Specialized OP-Amps
• High Current and/or High Voltage
ET 238B – OP-Amps
• Specialized OP-Amps
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Sonar send/receive modules
Multiplexed amplifiers
Programmable gain amplifiers
Automotive instrumentation and control
Radio/audio/video ICs
ADCs and DACs
• General Purpose OP-Amp
• Circuit Symbol and Terminals
• Figure to the right
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Reference Designator - per drawing
Negative and Positive Supply Terminals
Inverting input terminal - Negative terminal
Non-inverting input terminal - Positive terminal
LM741J
ET 238B – OP-Amps
• General Purpose OP-Amp
• Simplified Circuitry of a 741 OP-Amp
Image from a
National
Semiconductor
data sheet.
ET 238B – OP-Amps
• General Purpose OP-Amp
• Simplified Circuitry of a General Purpose OP-Amp
• Input Stage - Differential Amplifier
• The difference of the voltage across the Inverting and Noninverting Inputs Ed
• Very high gain amplifier
• Intermediate Stage - Level Shifter
• Shifts the DC level of Input stage to match the input requirements
of the Output Stage
• Specifically to bias the output stage
• The biasing is necessary to allow the Input stage generated voltage
to the Output almost unchanged
• Output Stage - Push-Pull
• Most common - pnp-npn circuit
• Supports a high current output
ET 238B – OP-Amps
• OP Amp Terminals
• Ideal OP-Amp Characteristics
• Has infinite Gain
• Has Infinite Input Resistance
• Has Zero Output Resistance
• Real Power Supply Terminals
• Typically Three Power Supply Terminals
• V+ Connected to the OP-Amp
• V- Connected to the OP-Amp
• Usually symmetrical +15V up to +18
• Can be unipolar
• Power Supply Common Not directly connected to the OP-Amp
• Return path for current back to the Power Supply
• Connected through the load to the OP-Amp
• May or May-not be connected to ground
• Real Output Terminals
• Single -ended output
• Voltage referenced to the Power Supply Common
ET 238B – OP-Amps
• OP Amp Terminals
• Real Output Terminals
• Current Limits
• Usually 5 to 10 mA
• Voltage Limits
• Output transistors need some of the supply voltage across the
transistor
• Otherwise it acts as a switch - not an amplifier
• With bipolar transistors - 1 to 2 volts needed
• With MOS Transistors a few millivolts are required
• Thus w/bipolar and +15 Supplies +Vsat = +14V and - Vsat = -13V
• Circuit Protection
• Usually have circuits to limit output current to 25 mA for a short
• Prevents burnout
• Load Resistance limits - 2k
ET 238B – OP-Amps
• OP Amp Terminals
• Input Terminals
• + and - Terminals
• Differential Input Terminals
• Vout depends on the difference between the input terminals times
the gain of the amplifier AOL.
• Ed = {V + input} - {V - input}
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Both are measured with respect to common
Vout = Ed times AOL.
Polarity matches the input - If + Input more positive then + Out
If - Input more positive then - Out
• Input Bias Currents and Offset Voltage
• Input Bias Currents
• Small currents used to activate the input transistors
• Offset Voltages
• Small imbalance voltages on the input terminals
ET 238B – OP-Amps
• Open Loop Voltage Gain
• Definition
Vout = Ed times AOL
• Typical circuits (per Nation Semiconductor’s OP-Amp Circuit
Collection Application Note 31) www.national.com/an/AN/AN-31.pdf
ET 238B – OP-Amps
• Typical circuits (per Nation Semiconductor’s OP-Amp Circuit
Collection Application Note 31) www.national.com/an/AN/AN-31.pdf