低成本自動應急燈電路

低成本自動應急燈電路
低成本自動應急燈電路,Lowcost/AutomaticEmergencyLight
Description--------------------------------------------------------------------------------Hereisawhite-LED-basedemergencylightthatoffersthefollowingadvantages:1.ItishighlybrightduetotheuseofwhiteLEDs.2.Thelightturnsonautomaticallywhenmainssupplyfails,andturnsoffwhenmainspowerresumes.3.Ithasitsownbatterycharger.Whenthebatteryisfullycharged,chargingstopsautomatically.Thecircuitcomprisestwosections:chargerpowersupplyandLEDdriver.Thechargerpowersupplysectionisbuiltaround3-terminaladjustableregulator(IC1)LM317,whiletheLEDdriversectionisbuiltaroundtransistorBD140(T2).Inthechargerpowersupplysection,inputACmainsissteppeddownbytransformertodeliver9V,500mAtothebridgerectifier,whichcomprisesdiodes(IN4007x4).Filtercapacitor(25v/1000uf)eliminatesripples.UnregulatedDCvoltageisfedtoinputpin3ofIC1andprovideschargingcurrentthroughdiodeIN4007(D5)andlimitingresistor(16ohm)R16.Byadjustingpreset2.2K(VR1),theoutputvoltagecanbeadjustedtodelivertherequiredchargingcurrent.Whenthebatterygetschargedto6.8V,zenerdiodeconductsandchargingcurrentfromregulator(IC1)findsapaththroughtransistorBC547(T1)togroundanditstopschargingofthebattery.TheLEDdriversectionusesatotaloftwelve10mmwhiteLEDs.AlltheLEDsareconnectedinparallelwitha100-ohmresistorinserieswitheach.Thecommon-anodejunctionofallthetwelveLEDsisconnectedtothecollectorofpnptransistorT2andtheemitteroftransistorT2isdirectlyconnectedtothepositiveterminalof6Vbattery.TheunregulatedDCvoltage,producedatthecathodejunctionofBridge(Diodes),isfedtothebaseoftransistorT2througha1kresistor.Whenmainspowerisavailable,thebaseoftransistorT2remainshighandT2doesnotconduct.ThusLEDsareoff.Ontheotherhand,whenmainsfails,thebaseoftransistorT2becomeslowanditconducts.ThismakesalltheLEDs(LED1throughLED12)glow.Themainspowersupply,whenavailable,chargesthebatteryandkeepstheLEDsoffastransistorT2remainscut-off.Duringmainsfailure,thechargingsectionstopsworkingandthebatterysupplymakestheLEDsglow.Assemblethecircuitonageneral-purposePCBandencloseinacabinetwithenoughspaceforbatteryandswitches.MounttheLEDsonthecabinetsuchthattheylightuptheroom.Aholeinthecabinetshouldbedrilledtoconnect230VACinputfortheprimaryofthetransformer.Ihavetestedthecircuitwithtwelve10mmwhiteLEDs.YoucanusemoreLEDsprovidedthetotalcurrentconsumptiondoesnotexceed1.5A.DrivertransistorT2candeliverupto1.5Awithproperheat-sinkarrangement.