LED DRIVE CIRCUITS.docx
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LED DRIVE CIRCUITS.docx
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LEDDRIVECIRCUITS
1.LEDCircuitConsideration
OptimallypoweringwhiteLEDsrequiresspecializedregulatorsthatbothovercomethehighforward-voltageoftheLEDandprovideconstant-currentdrivetominimizeintensityvariationswithbatteryvoltageandbetweenLEDs.Forthispurpose,therearetwomainstreamregulatortypes:
inductor-basedboostconvertersandcapacitor-basedcharge-pumpconverters.Eachregulatortypehasspecificadvantages/disadvantages,sooptimalselectiondependsonthesystem'sparticularpriorities.
LEDCircuitEfficiencyandStability
IntheworldofcustomLEDlighting,itisextremelyimportanttounderstandtherelationshipbetweencircuitstabilityandcircuitefficiency.AstableLEDcircuitislessresponsivetovariationsinsourcevoltage.However,thecircuitdissipatesmoreheatfromtheresistorandisthereforelessefficient.Anunstablecircuitismoreefficient,butvariationsinsourcevoltagewillcausedramaticfluctuationsincurrent.Thiscanleadtooverdrivenlightemittingdiodescausingdamage,orifunderdriven,theLEDlightsmaynotlightatall.WhendesigninganLEDcircuitwithcurrentlimingresistorcircuit,thegoalistofindthebestcompromisebetweenstabilityandefficiency.Toaccomplishthis,itisbesttoconsiderafewdifferentvariationsofthesameLEDdrivercircuitinanattempttodeterminethemostfeasiblesolution.ThisbecomesextremelycriticalwhendesigningforLEDtaillights.
2.Powersupplyfordrivingcircuits
1)Lowdrivingvoltage(theavailablevoltageislowerthantheforwardvoltage)
Applications:
LEDflashlights,emergencylamps,energy-savinglamps.
Solutions:
BoostConverter(usinginductancetostoretheenergy)
Requirements:
lowcost,highefficiencyinconverting,smallvolume
2)Transitionaldrivingvoltage
Sometimestheavailablevoltagesupplyishigherthantheforwardvoltage,whilesometimeslower.
Application:
LEDminer'slamp
Solutions:
reversepolaritychargepumpconverter
3)highdrivingvoltage
Applications:
lawnlamp,headlights..
Solutions:
series-wound switchesbuckconverter
4)Commercialpowersupply
Requirements:
Voltagereduction,currentrectification,highchangingefficiency,lowcost,smallinsize.
<1>SmallandmediumpowerconsumingLEDs:
single-endfly-backconverter
HighPowerconsumingLEDs:
bridgecircuit
3.Typicaldrivingcircuits--drivers
i.Capacitor-basedbuckconverter
ii.UsingSCR
iii.Usingfilteringunit
iv.Mostsimplifyingwayofusingcapacitorstoreducethevoltage
1.Typicalvoltage-reducingdrivecircuitforLEDs
4.Typicalon-chipICsforuse
i.RGBLEDdriverSTP24DP05
Application:
LCDmonitors
TheSTP24DP05isamonolithic,lowvoltage,lowcurrentpower24-bitshiftregisterdesignedforLEDpanELdisplays.Thedevicecontainsa8x3-bitserial-in,parallel-outshiftregisterthatfeedsa8x3-bitD-typestorageregister.Intheoutputstage,twenty-fourregulatedcurrentsourcesweredesignedtoprovide5-80mAconstantcurrenttodrivetheLEDs.
ii.ChargepumpsfordrivingwhiteLEDs
iii.RunninganLEDwithpulsestogetmaximumbrightness
TogivemaximumbrightnessanLEDneedstobedrivenbyapulsecircuit.Inthisway,itispossibletoput0.5AmpcurrentpulsesthroughanLEDatafrequencyofaround100Hzwhichfoolstheeyeintothinkingthatitseesacontinuouslight.
IftheLEDisrunat0.5Ampsforverylong,itwillburnout(usuallywithinafractionofasecond).Bykeepingthepulsedurationrelativelyshort,wecanavoidoverheatingtheLED.
Thiscircuitallowsadjustmentofthepulsewidthsothatthemaximumaveragecurrentisnomorethan50mA.
ToensurelongLEDlife,itshouldbeadjustedformaximumbrightnessthenreducedslightlytoanaveragecurrentofaround40mA.OneortwoLEDscanbedrivensimultaneously.C1canbearound1000uFandactsasareservoirbecausetheaveragebatteryisunabletosupplyhalfAmppulsesofcurrent.Thecircuitcanberunfromabatteryordcsupplyof9to12volts.
Wehadintendedtosupplyallthepartsasakitbutwe'vehadonly2enquiriesintwoyears.However,youshouldbeabletoorderallthecomponentsfromMaplinElectronicsintheUK.
iv.LEDDriveCircuit(SM-CCP-20W)
LEDDriveCircuit(SM-CCP-20W)
ProductDescription
[SM-CCP-20W]isaconstantcurrentLEDdrivecircuitusingICmanufacturers,thecircuitissimpleandefficient.Nocapacitors,resistorsbuck.Smallheat,Circuitreliable,easytoEMItesting.Forsupportingtheuseofhigh-powerLED.Maximum22-1WLED.WidelyusedLEDlights,spotlights,lightscups,lamps,etc.
[SM-CCP-22W--usingsingle-sidedPCBdesign.Coatwithamoisturerole.
Technicalparameters
Automaticallyadaptinginputvoltagerange:
90-265VAC
Outputcurrent50-54-350mA+-15%(200336)
Rated:
20W
LEDvoltage:
10-60V
Efficiency:
80%
AutomaticadaptationofcolorLEDavoidalotofresistanceadjustment.
Compact:
Long-**width=76*43*32mm
Model:
SM-CCP-20W
Company:
XiangshanSolarmaxPhoto-ElectricCo.,Ltd
A.
ballastresistor
Otherconsiderations:
stabilityofcurrentandelectricalefficiency
“Voltage-coefficient”wayofcalculatingthepropertiesofthecircuit
Voltage-coefficient:
(3)
Stabilityofcurrent:
(%)(4)(假定
);
Electricalefficiencyη=
(%)(5);
Ballastresistor:
R=
(Ω)(6);
Sourcevoltage:
U=
(V)(7)
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