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| Design Idea DI-131 LinkSwitch-TN Application LED Lighting Device LNK306DN (R) LED Driver for Halogen Light Bulb Retrofit Power Output 3W Input Voltage 85-265 VAC Output Voltage Topology 10 VTYP (9-15 V), 300 mA Non-isolated Buck Design Highlights * FitsinsidestandardGU10lampbase * Constantcurrent(CC)output * DrivecurrentindependentofLEDVFvariations * Tightlineregulation(5%)forconstantlightoutput * Noannoyinglinefrequencyflicker * Universalinputvoltagerange * Asingledesigncanbesoldworldwide * Consistentlyhighefficiencyacrossentirerange * MeetsEN55022BconductedEMIlimits * Completeovervoltageandovertemperatureprotection * Operatesunloaded:canbetestedwithouttheLEDs * Auto-restart:withstandsshortedoutputindefinitely * Thermalshutdown:protectsentirelampassembly DiodebridgeBR1rectifiestheACinputwhilecapacitorsC1 andC2filterit.InductorL1andRF1attenuateconductedEMI. Incaseofacomponentfailure,RF1willactasafuse. TheMOSFETwithinU1,diodeD3,inductorL2andcapacitor C3 form the buck converter stage. The controller within U1regulatestheoutputcurrentbyenablinganddisabling MOSFETswitchingcycles. During normal operation, the output current develops a voltagedropacrossR8andR10,whichisimpressedacross C6. When the voltage across C6 exceeds theVBE of Q1, Q1 and Q2 both turn on. When Q2 turns on, current is injectedintotheFEEDBACK(FB)pinofU1fromC5,via R3.WheneverthecurrentintotheFBpinexceeds49mA, MOSFETswitchingisdisabled.Thecontrolleradjuststhe ratioofenabledanddisabledcyclestoregulatetheoutput currentat330mA. Duringno-loadoperation,theoutputvoltageissensedby D1,D2andC2.ThevoltageacrossC5feedscurrentinto theFBpinofU1throughdividerR7andR1.TheFBpin R7 30 k Q2 MMST3906 R3 10 k R1 4.7 k R9 4.7 k D1 BAV21WS-7-F D2 BAV21WS-7-F Operation The non-isolated buck converter shown in Figure 1 was designedaroundamemberoftheLinkSwitch-TNICfamily, the LNK306DN (U1). A LNK306 was selected since its minimumcurrentlimit(450mA)ensuresthatitwillbeable todelivertherequired330mAofoutputcurrent. C5 100 nF 25 V R6 10 k R4 10 k C6 100 nF 25 V R8 2 R10 12 L2 1 mH C3 2.2 F 25 V R11 1 k Q1 MMST3904 9-15 V, 300 mA J3 C4 100 nF 25 V FB BP S D L 85-265 VAC N RF1 10 2.5 W BR1 MB6S 600 V C1 4.7 F 380 V L1 1 mH C2 4.7 F 380 V LinkSwitch-TN U1 LNK306DN D3 MURS160T3 J4 PI-4575-030707 Figure 1. 3 W LED, Halogen Bulb Replacement using LinkSwitch-TN in Non-Isolated Buck Converter Technology. DI-131 March 2007 DI-89 DI-131 voltageisspecifiedas1.63Vat49mA,whichallowsittobe usedasareference.Theoutputvoltageisregulatedto<18V bydisablingMOSFETswitchingcyclesasthecurrentintothe FBpinexceeds49mA. dBV 70 60 50 40 30 20 10 0 -10 -20 0.15 1.0 10.0 100.0 QP AV QP AV PI-4579-021207 80 Key Design Points * TopreventEMIcouplingbetweentheswitchingnodeson themainboardandtheinputfilterboard,ashieldboard (connectedtoC2negative)wasplacedbetweenthetwo PCboards(seeFigure3).Thisgreatlyimprovedthe margintotheconductedEMIlimits. * DiodesD1andD2canbereplacedbyasingle600V diode.Two250Vdiodeswereusedbecausetheytookup lessspacethanasingle600Vdiode. * IncreasingthevalueofC3willreducetheripplecurrent throughtheLEDloadattheexpenseofincreased componentsizeandcost. * Pre-loadresistorR11ensurescorrectno-loadoperation, whichenablesthepowersupplytobetestedwithoutthe loadconnectedtoit. * VerifythatL2doesnotsaturateheavilyatthemaximum currentlimitofU1(647mA).RefertotheInductor Manufacturer'sL-20%currentrating. * Inlessthermallychallengedenclosures,theFBpincan beusedtodirectlysensethevoltageacrossresistors R8andR10.ThiscaneliminateQ1,Q2andassociated components,butrequiresthecurrentlimitsensevoltage toincreasefrom0.65Vto1.65V.Thiswillincreasethe senseresistordissipationbyabout300mWandcausethe internalambienttemperatureofthesupplytoincrease. * MaximizethePCBareathattheU1SOURCEpins connectto,foroptimalheatsinking. * Sincethisdesigndoesnotprovideinputtooutput isolation,theloadLEDsmustbeisolatedfromtheuservia thelightbulbenclosure. MHz Figure 2. Worst Case Conducted EMI (230 VAC). 0.780" TOL 0.050" 1.080" 1.024" 0.742" 0.614" PI-4577-030707 Figure 3. Assembled Unit, Dimensions: 0.78 x 1 inch (19.8 x 25.4 mm). For the latest updates, visit www.powerint.com Power Integrations reserves the right to make changes to its products at any time to improve reliability or manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications illustrated herein (transformer construction and circuits external to the products) may be covered by one or more U.S. and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A complete list of Power Integrations' patents may be found at www.powerint.com. Power Integrations grants its customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm. The PI logo,TOPSwitch, TinySwitch,LinkSwitch, DPA-Switch,PeakSwitch,EcoSmart, Clampless,E-Shield,Filterfuse,StackFET,PI ExpertandPI FACTS are trademarks of Power Integrations, Inc. Other trademarks are property of their respective companies. (c)2007, Power Integrations, Inc. Rev. B 03/07 Power Integrations 5245 Hellyer Avenue San Jose, CA 95138 Phone: 1-408-414-9200 Apps: 1-408-414-9660 Apps Fax: 1-408-414-9760 For a complete listing of worldwide sales offices, please visit www.powerint.com |
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