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C ir cu it P r o te c t i o n , T i p s , a n d T r o u b l es h oo t i n g

C ir cu it P r o te c t i o n , T i p s , a n d T r o u b l es h oo t i n g. Fall 2014 E C E 445. Be c o mi n g a Good D es i gn Engine e r. Understand t h e p r obl e m Understand t h e c on str ain ts you ha ve Understand p re v iou s app r oa c h es t o t h e p r obl e m a t hand

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C ir cu it P r o te c t i o n , T i p s , a n d T r o u b l es h oo t i n g

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  1. CircuitProtection, Tips, and Troubleshooting Fall 2014 ECE445

  2. Becoming aGood Design Engineer • Understandtheproblem • Understandtheconstraintsyouhave • Understandpreviousapproachestothe problemathand • Endgoalofseniordesign: • –Solveproblemsyouhaven’tbeenfacedwithandbe innovative • Butfirst:backgroundknowledgeisrequired

  3. Circuit Connections • Payattentiontopolarity LongerLead: Positive Electrolytic capacitor ShorterLead: Negative GOOD BAD

  4. Ratings • Determinepart ratings • Allcomponentsarerated • Capacitors: • – Ifthevoltageacrossthecapacitor isgoingtobe50[V],shouldyouuseacapacitorthat isratedto50[V]? • Resistors:maximumpowerdissipation • P= i2*RorP= v2/R • Example: • – P= (5e-3)2*1e4 • i.e.thepowerdissipatedwithoutburning itout= 250mW FromNewarkElectronics

  5. DataSheets • Byreadingthedatasheet: • Providepin-layouts • Deviceratings • Potentialapplications

  6. VoltageCurrent Limiting • Fuses:typicallyallowfor passageof“normal”current • Afusewill“blow”aboveits currentrating • Diodes: • ConductwhenV>0.7V • Bestsolution:usebothdiodes andfuses • Fuses

  7. Voltage/CurrentProtection Examples Current acrossresistor typically=20mA FusesandDiodeCombination Current LimitingResistor

  8. Device Polarity • Thelonger length isthe(+)terminal • Capacitor • Polarity: tantalumorelectrolytic Nopolarity:ceramicorpolyester (-) (-) (+) • (+) • Diode Thebarindicatescathode (+) (-) (-) (+) http://academic.evergreen.edu/projects/biophysics/technotes/electron/leds.htm/ http://electrapk.com/zener-diode/

  9. Reverse PolarityProtection Below are2differentconfigurationstoensurecorrectvoltagepolaritytothecircuit. Circuit willnot operatewithincorrectpolarity “DiodeBridge” Circuit willoperateundereitherpolarity, but willhavehigherlosses Wikipedia

  10. Power SupplyBypass/ Decoupling Capacitors • Bypasscapacitors • Takesnoisetoground • Rephrased:basically shuntsACsignalsto ground • Typicalvaluesrange from:0.1uF • Largersizecapacitors forhighersupply voltages *Picture http://www.physics.udel.edu/~nowak/phys645/The_bipolar_transistor_files/image013.jpg

  11. EarthGround vs“Ground” • Greenterminalis earthground • Blackterminalsare signalgrounds • Knowthe difference! EarthGround Floating Ground

  12. Potentiometers • Variableresistors • ExampleisatrimpotwithR=10KOhms • From(a)to(c), • R1=6KOhms • From(b)to(c), • R2=4KOhms (b)R2=4k (a)R1=6k ToRestof Circuit (c)

  13. Resistor Codes METRIC-TO-AWGCONVERSIONTABLE • ReadingSurface MountResistors Metric Size mm2 0.5 0.8 1.0 2.0 3.0 5.0 8.0 13.0 19.0 32.0 52.0 AWG Size 20 18 16 14 12 10 8 6 4 2 0 • A resistor marked332is • 3.3kilo-ohms • 3K3is3.3 kilo-ohms • Knowwiregauges ResistorValueChart

  14. WireGauges • Wiregauge isastandardforthesizeofthewire (proportionaltocurrentrating) • Typicalwireinlab is22AWG (AmericanWire Gauges) • 52.9mΩ/meter • 7Aforshortwiring • 0.92Aforpowertransmission • http://www.powerstream.com/Wire_Size.htm • Breadboardinthelabcanonlyuse22AWGor smaller,otherwise itwill damagetheclips • http://www.how-to-wire-it.com/romex-cable.html

  15. Driving HighCurrent Load • Mostmicroprocessor/TTLcandrive<20mA,that is approximatelyanLED. • InterfacemicroprocessorI/Owithagate. • Letthegatebreakinsteadofthemicroprocessor! • Methods • Relays • maywearoutandhavedelays • Transistor • fastswitchingbuthavecurrentlimit • H-bridge • allows forwardandreversecurrent • goodformotors • http://www.acroname.com/robotics/info/articles/drivers/drivers.html

  16. Troubleshooting Steps(1/2) • Checksupplyvoltageusingthemultimeter • Ispowerpluggedin?Isanyswitchoff?Isthefuseblown?Areallthe breadboardbusstripsconnectedtoVDD/GND? • ProbesignalatintermediatestagesorindividualfunctionblocksI/O • Equipmentavailable: • Fordigitalsignals:LogicAnalyzer,LEDs • Foranalogsignals:Oscilloscope,Voltmeter,SpectrumAnalyzer • Checkinterconnections • Isanythingmis-wired?Areanywires loose?Areanycontactsbad?Is anysignalfloating?

  17. Troubleshooting Steps(2/2) • Doublecheckthedesign • Checkthepindiagram • Checkthatyouhavethecorrectdatasheetforthepartnumber • Re-analyzethelogic,gothroughsomecalculation • Ensurecorrectpolarity(refertothenextslide) • Faultydevices/breadboard(Lastresort ifallelsefails!) • Replace/rewire onepartatatime,testaftereverychange • Isolatethepartsundertestfromtherestofthecircuit

  18. References • http://www.intersil.com/data/an/an1325.pdf • http://en.wikipedia.org/wiki/Diode • http://en.wikipedia.org/wiki/Fuse_(electrical) • http://www.learnabout-electronics.org/resistors_07.php • http://www.rbeelectronics.com/wtable.htm • PreviousECE445LectureSlides • StaffoftheECEElectronicsShop, • DanMast,MarkSmart,SkotWiedmann

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