ELECTRIC CIRCUITS ECSE2010 Spring 2003 Class 8

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ELECTRIC CIRCUITSECSE-2010Spring 2003 Class 8

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ASSIGNMENTS DUE

• Today (Thursday)
• Will do Experiment 3 In Class (EP-3)
• Activities 8-1, 8-2, (In Class)
• Next Monday
• Homework 3 Due
• Activity 9-1, Op-Amp ILM
• Next Tuesday/Wednesday
• Activity 10-2 (There is no 10-1)
• Will do Experiment 4 in Class (EP-4)

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FINAL EXAM

• Wednesday, May 7
• 8-11 AM
• Room(s) to be Announced at a Later Date
• Please Note on Your Schedules
• Everyone Must Take the Final Exam

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REVIEW

• Source Conversions
• Any Voltage Source, vs in Series with Resistor,
  Rs, May be Replaced by a Current Source, is vs
  / Rs, in Parallel with Same Resistor, Rs
• Sometimes a Useful Technique
• Often Simplifies a Problem
• Not Always the Best Technique to Use
• Be Very Careful with Controlled Sources
• Sometime lose controlling v, i, when make
  source conversion

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REVIEW

• Superposition
• A technique to use when there is more than 1
  Independent Source in a circuit
• Not always the best technique to use
• Will learn lots of techniques Experience helps
  us learn which technique to choose
• Find Output due to each independent source with
  all other independent sources set 0
• Source of 0 is called a dead source
• Dead voltage source 0 V Short Circuit
• Dead current source 0 A Open Circuit

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REVIEW

• Superposition (Continued)
• Total Output Sum of all Outputs due to each
  independent source with all other independent
  sources dead
• Simply Add them
• Works only for Linear Circuits Only kind we will
  consider
• Leave Controlled Sources Alone!!
• Find Outputs due to Independent Sources only
• Do NOT set Controlled Sources 0

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REVIEW

• Source Network
• Resistors, Controlled Sources and at least 1
  Independent Source
• Thevenin Equivalent Circuit
• Can Replace any Source Network with Voltage
  Source, voc, in Series with Resistor, RT
• Norton Equivalent Circuit
• Can Replace any Source Network with Current
  Source isc, in Parallel with Resistor, RT

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SOURCE CONVERSIONS

• Define v, i using Active Convention

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THEVENIN EQUIVALENT CIRCUIT

• Define v, i using Active Convention

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NORTON EQUIVALENT CIRCUIT

• Define v, i using Active Convention

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THEVENIN/NORTON CIRCUITS
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ACTIVITY 8-1
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ACTIVITY 8-1

• Use Thevenins Theorem to Find the DC Bias Point
  of a Bipolar Junction Transistor (BJT)
• Find the Thevenin Equivalent Circuit for
  everything to the LEFT of the BJT
• Find the DC Bias Point

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ACTIVITY 8-1

• Could Solve Using Node Equations or Mesh
  Equations, but it is Much Easier to First Find
  the Thevenin Equivalent Circuit for everything to
  the LEFT of the BJT
• This Will Allow Us to Easily Find ib, Which Then
  Determines Everything Else in the Circuit

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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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ACTIVITY 8-1
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REAL SOURCES
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REAL SOURCES

• See Plot of i vs v for Voltage Source
• Voltage decreases as Current increases
• For small Currents Model with Linear Curve
• Slope of Straight Line - 1 / Rs
• Rs is called the Source Resistance
• Model for Real Voltage Source is Ideal Voltage
  Source, Vs, in Series with Source Resistance, Rs
• Can also be viewed as the Thevenin Equivalent Ckt
  for a more complicated Source Network

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REAL SOURCES
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REAL SOURCES

• For the Function Generator
• Rs 50 ohms
• Designed that Way
• When Modeling Function Generator, Use Measured
  Open Circuit Voltage (Voltage when No Current
  Flows) in Series with 50 Ohm Resistor
• Will use this in later Experiments

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POWER TRANSFER

• Can Model Any Source Network with its Thevenin
  Equivalent Ckt
• Vs in series with Rs if Voltage Source
• voc in series with RT if More Complicated Network
• Can Model Any Load Network with its Equivalent
  Resistance
• Req v / i

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POWER TRANSFER
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DESIGN PROBLEM

• Rs is Usually Fixed
• Determined by Voltage Source or Source Network
• Load is Chosen by Designer
• We Usually Have Some Control Over This
• How Do We Choose Req to Get Maximum Power to
  Load?
• Choose Req Rs
• Will See Example in Activity 8-2

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MAXIMUM POWER TRANSFER
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ACTIVITY 8-2
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ACTIVITY 8-2

• Replace Source Network with Thevenin Equivalent
  Circuit
• Open Circuit Output
• voc 30 / (30 6) 24 20 V
• RT 6 // 30 5k

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ACTIVITY 8-2
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ACTIVITY 8-2
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ACTIVITY 8-2

• Replace Source Network with Thevenin Equivalent
  Circuit
• voc 30 / (30 6) 24 20 V
• RT 6 // 30 5k
• For Maximum Power to RL
• Want RL RT 5k
• How can we model this using PSpice?

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ACTIVITY 8-2

• To Vary the Value of an Element in a PSpice
  Circuit File
• Put Element in in Circuit File
• Use .param Statement
• Use .dc Statement
• R30 3 0 RL
• Resistor Called R30
• Connected between Node 3 and Node 0
• Value of Resistor is Variable

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ACTIVITY 8-2

• .param RL 0.1k
• Parameter to be varied is called RL
• Nominal value of RL .1k (starting point)
• .dc lin param RL .1k, 16k, .1k
• Perform a DC Analysis at each Value
• Linearly change the parameter RL
• Vary RL from .1k to 16k in steps of .1k

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ACTIVITY 8-2

• To Find Power in RL
• pL vL x iL
• PSpice will calculate all currents and voltages
• Multiply vL by iL in Probe
• Plot

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ACTIVITY 8-2

• Circuit File
• Activity 8-2
• v10 1 0 dc 24
• R12 1 2 6k
• R20 2 0 30k
• R30 2 0 RL
• .param RL .1k
• .dc lin param RL .1k, 16k, .1k
• .probe
• .end

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ACTIVITY 8-2

• Circuit File Has Been Simulated
• Run PSpice A/D
• FILE gt Open
• C/files/ce-studio/circuits/act_3.1.dat
• TRACE gt Add
• i(R30) v(3)
• TRACE gt Cursor gt Display
• Click on Graph gt note cursor
• TRACE gt Cursor gt Peak gt Read Value
• PMAX at RL 5 k ohms

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ACTIVITY 8-2
Using Schematics
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ACTIVITY 8-2

• With Schematics
• Show RL as a Variable Resistor
• Doubleclick on Variable Resistor
• Set its Value as RL
• Change Set from .5 to 1.0
• Add Parameters from Parts
• Doubleclick on Parameters
• Choose Name1 RL, Value1 1k (Any Nominal Value
  in Range)

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ACTIVITY 8-2

• With Schematics
• Click Setup Analysis
• Choose DC Sweep then Doubleclick
• Choose to Sweep a Global Parameter
• Choose a Linear Sweep
• Set Name of parameter RL
• Set Start Value .1k
• Set End Value 16 k
• Set Increment .1k
• Click Simulate Plot i(RL) v(RL)

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RECALL EXPERIMENT 2a

• For a Load Network
• Replace Load Network with Req
• Plot i vs v gt Straight Line
• Passes Through i v 0
• Slope 1 / Req
• Best Slope When Have Random Errors Method of
  Least Squares
• We did this in Experiment 2a Just Yesterday

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EXPERIMENT 2a
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EXPERIMENT 3a

• For a Source Network
• Replace with Thevenin Equivalent Circuit
• Plot i vs v gt Straight Line
• Does NOT Pass Through i v 0
• Crosses v axis at voc
• Crosses i axis at voc / RT isc
• Slope - 1 / RT
• Best Slope When Have Random Errors Method of
  Linear Regression
• This is Experiment 3a

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EXPERIMENT 3a
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EXPERIMENT 3a
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EXPERIMENT 3a

• Model with Thevenin Equivalent Circuit
• If Open Circuit RL i 0
• Measure v voc with Multimeter
• Connect RL
• Measure voltage, v, across RL with Multimeter
• Change RL until v .8 voc Record v

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EXPERIMENT 3a

• Disconnect RL and Measure with Multimeter
• Calculate i v / RL
• Change RL until v .6 voc, etc Measure v, RL
• Take at least 5 data points for v, RL
• Calculate i at each point
• Use as many Significant Figures as possible
• Plot v vs i or i vs v Find best voc and RT using
  Method of Linear Regression as Explained in Notes

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EXPERIMENT 3b

• OPTIONAL BUT ENCOURAGED!!
• Build the Circuit Analyzed in Activity 8-1
• Take Protoboard Home for Weekend
• Pick Up All Parts
• 1-PN2222 Transistor
• 2-10k Resistors 2-1k Resistors
• Bring to Class on Monday
• Measure DC Bias Point Compare with what you
  calculated
• Keep on Protoboard Will Use Again Later

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PINS FOR A TRANSISTOR
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END OF UNIT I!!

• Exam I will Cover Classes 1-8
• Exam I is Monday, 2/10, 7-9 pm
• Will Review for Exam I Next Week Thursday
• Will Start Unit II on Monday