高效高功率闪光灯设计技巧

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1、AND8135/DEfficientHighPowerFlashLightPreparedby:MichaelBairanzadeONSemiconductorhttp://onsemi.comAPPLICATIONNOTEINTRODUCTIONDependinguponthetypeofflashinvolved,theamountofenergystoredintocapacitorC1canbealow10Joule(smallAlthoughthexenonlampsdominatethestandardcameracamera)tothousandofJoule

2、forprofessionalapplications.market,theyarenotapplicableintheportablephone.Asamatteroffact,thelargereservoircapacitorandhighvoltageassociatedwiththexenonflashmakesuchaconceptnot+260Vsuitableforthecellularphoneequipments.ThesemiconductorbasedWhiteLEDdevicesprovidetherightchoicewhenlimitedfla

3、shlightbecomesnecessarytoilluminateaphotographicscene.ThispaperdepictstheR11basicsofthexenonconceptanddetailsatypicalWhiteLED470kX1flashapplication.S1+3C2XENONLAMPCONCEPTTRIGGER4.7F/T1AlowpressureofararegasmixturefillsaglassenvelopeC2XENONTUBE300V100nF/withtwoendselectrodesonbothsides.Ins

4、teadystate,the2300VvoltageacrosstheelectrodesissettoavaluewellbelowthetriggervoltageasdepictedFigure1.Atthispoint,nocurrentflowsandthesystemisstableuntilatriggervoltageisGNDappliedtothethirdelectrode.Thishighvoltagepulse,intheFigure2.BasicXenonFlash1kVrange,comesfromatransformerbuiltwithas

5、mallmagnetictoretriggeredbyanabruptdischargeoftheThenetadvantageofsuchaconceptistheveryshortcapacitorC2(seeFigure2).pulse,makingeasysnapshotphotostocapturemovingstuffs.ThedrawbacksarethelargephysicalsizeoftheIreservoircapacitorandtherecycletimeneededtorechargethecapacitorbetweentwoshots(in

6、the5secrangeforconsumerapplications).Clearly,thesedrawbacksmakethexenonbasedflashnotsuitableforhandheldcellularphone,withlimitedsizeandenergysupply.WHITELEDFLASHVVCCToovercomethephysicalsizelimitation,theflashconceptistomakeprofitofthehighefficiency,intermoflight,comingfromthemodernwhiteLE

7、D.VtrigWitha4Vforwarddropvoltage,suchdiodesdonotneedextrahighvoltagetriggerpulse,theyareextremelyfasttoturnON/OFFandalltheassociatedelectroniccircuitcanbehousedinsideastandardportablephone.SincethewhiteFigure1.XenonFlashBreakdownVoltageLEDhaveelectricalcharact