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UK EE 462G - Electronic Circuits Laboratory EE462G

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Electronic Circuits Laboratory EE462G Lab #3InstrumentationSlide 3Ideal Diode ModelAnalysis of Diode CircuitExampleSPICE Set Up and ResultExampleExample with SPICESlide 10Test Circuit ATest Circuit BTest Circuit CTest Circuit DOther NotesStray Capacitance ModelsSlide 17Power Analysis ExampleBranch CurrentsPower FormulaeRMS Circuit ValuesPower AnalysisMatlab Symbolic ComputationsFinal NotesSlide 25Electronic Circuits LaboratoryEE462GLab #3Diodes, Transfer Characteristics, and Clipping CircuitsInstrumentationThis lab requires:Function Generator and Oscilloscope (as in Lab 1)Tektronix’s PS 280 DC Triple output (one fixed 5V / 3A and 2 variable 0 to 30V / 2A) Power SupplyWhat advantages are there to a chassis ground over an earth ground for a power supply? chassis groundInstrumentationThe 2 variable outputs of the power supply will be used for batteries (DC series sources) in the experiments’ circuits: 10k Vs Vout V1 + - V2 Minus TerminalPlus TerminalLET CHASSIS GROUND FLOAT!Ideal Diode ModelDiode junction acts as a short circuit for forward bias (VD > 0 (anode positive)).Diode junction acts as an open circuit for reverse bias (VD < 0 (anode negative)).Near-Ideal Diode ModelAdd a 0.7 voltage source for the forward offset voltage in series ideal diode with same polarity as the forward bias.Ideal Diode Model Anode Cathode+ Vd = 0 -Id Diode On Anode Cathode+ Vd -Id 0.7 VAnode Cathode- Vd +Id = 0 Diode OffAnalysis of Diode CircuitMethods of Analysis:Load-line analysisDiode-State AnalysisSPICEDiode-State AnalysisDetermine the on-off state of each diode by guessing a combination of on-off states.For on-diodes assume a forward biased current direction (0 volts) and for off-diodes assume a negative anode voltage (0 amps) and then analyze circuit. If guessed state results in an inconsistent voltage or current in circuit analysis, guess another state combination until all are consistent with circuit analysis.Problem:Use near-ideal model to determine the state of diode D1 when V1=10V. (First guess diode is off).Find range of V1 values such that D1 is off.Assume output is current I3 and input is V1, analytically find the transfer characteristics of this circuit.Solve via SPICE and plot:Example V1R1 1k D1R2 1k R3 1k I3In SPICEbuild circuit and insert diode (use default characteristics)Place ammeter at outputSet source to DC (value is not important)In “simulation set up” select (Dual) Parameter DC Sweep. Select V1 as parameter to sweep and indicate range and increment.Ask for graph output and run!SPICE Set Up and Result V1R1 1k D1R2 1k R3 1k VAm1V1 +900.000m I(VAM1) +352.554n D(V1) 0.0D(I(VAM1)) 0.0la2ex1-DC Transfer-2V1(Amp)0.0+1.000m-4.000 -2.000 0.0 +2.000 +4.000Example Sketch output waveform if input is a 5Vrms sinusoid of frequency 1kHz:Determine transfer characteristics from input through waveform output.Map input waveform through the transfer characteristics.Note that when diode is on:kVI34.1130 0.5 1 1.5 2 2.5 3 3.5 4 4.5x 10-3-8-6-4-202468Input VoltagesecondsVolts1.4 Volts 7.07 Volts 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5x 10-300.20.40.60.811.21.41.61.82x 10-3Output CurrentsecondsAmpsExample with SPICEFind output waveform if input is a 5Vrms sinusoid of frequency 1kHz:Build circuit in SPICESet source to sinusoid, but do not check AC box. Go to transient parameters tab and select appropriate amplitude (7.0711) and frequency (1000), the rest can be zero.Set up simulation parameters, select “Parameter sweep of transient,” select source with start and stop magnitudes to same value and step size to a non zero number (you don’t want it to sweep, and it will not use these number since AC box was not check in source set up).The set up transient parameters to appropriate start and stop time and increment.The run simulation. If too many waveform periods appear, such that waveform details cannot be easily seen, make start and stop time shorter.Example with SPICEFind output waveform if input is a 5Vrms sinusoid of frequency 1kHz:TIME -1.000 I(VAM1) -1.000 D(TIME) -1.000D(I(VAM1)) -2.753la2ex2--6time (s)(Amp)0.0+1.000m+2.000m0.0 +2.000m +4.000m +6.000m +8.000m +10.000mProblem:Given Vs is a 2.8 Vrms 250Hz sinusoid, find Vout (for power analysis a 5.1k load will also be considered)Analysis:Use .7 V forward offset voltage and ideal diode approximation. Can derive transfer characteristics or reason out directly.Lab Procedure:Describe function generator settings, oscilloscope probe placement, and oscilloscope settings. Record resulting waveforms for at least one period but not more than 5 (can use GPIB Program “Show_Wave” or save to a floppy disc).Test Circuit A 10k Vs Vout (A) + -Test Circuit B Problem:Given Vs is a 2.8 Vrms 250Hz sinusoid, find Vout without a load.Analysis:Use estimated forward offset voltage and ideal diode approximation. Can derive transfer characteristics or reason out directly. Lab Procedure:Describe function generator settings, power supply attachment with grounding issues, oscilloscope probe placement, and oscilloscope settings. Record resulting waveforms for at least one period but not more than 5. For the power analysis when circuit has a load, the DMM can be put in series with each branch to measure RMS current. 10k Vs Vout V1 + -Test Circuit C Problem:Given Vs is a 2.8 Vrms 250Hz sinusoid, find Vout without a loadAnalysis:Use estimated forward offset voltage and ideal diode approximation. Can derive transfer characteristics or reason out directly. Lab Procedure:Describe function generator settings, power supply attachment and grounding issues, oscilloscope probe placement, and oscilloscope settings. Record resulting waveforms for at least one period but not more than 5. 10k Vs Vout V1 + - V2Test Circuit D Problem:Similar to Circuit B: Does order of diode and DC source change output?Analysis:Does this affect the KVL or KCL equation?Lab Procedure:Power supply is isolated from earth ground; however stray capacitance from chassis ground to earth ground exists that practically affects the output. How will a capacitive path to ground at the 2 different points in Circuits B and D affect the output? Will this effect be observed at some frequencies better than others? 10k Vs Vout V1 + -Power:Recall instantaneous power is a product of the voltage and current waveforms. So for source power find


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