Design Idea DI-131
LinkSwitch®-TN
LED Driver for Halogen Light Bulb Retrofit
Application
Device
Power Output Input Voltage
3 W 85-265 VAC
Output Voltage
Topology
LED Lighting LNK306DN
10 VTYP (9-15 V), 300 mA Non-isolated Buck
Design Highlights
DiodeꢀbridgeꢀBR1ꢀrectifiesꢀtheꢀACꢀinputꢀwhileꢀcapacitorsꢀC1ꢀ
andꢀC2ꢀfilterꢀit.ꢀꢀInductorꢀL1ꢀandꢀRF1ꢀattenuateꢀconductedꢀEMI.ꢀ
Inꢀcaseꢀofꢀaꢀcomponentꢀfailure,ꢀRF1ꢀwillꢀactꢀasꢀaꢀfuse.
•ꢀ FitsꢀinsideꢀstandardꢀGU10ꢀlampꢀbase
•ꢀ Constantꢀcurrentꢀ(CC)ꢀoutput
•ꢀ DriveꢀcurrentꢀindependentꢀofꢀLEDꢀVFꢀvariations
•ꢀ Tightꢀlineꢀregulationꢀ(±5%)ꢀforꢀconstantꢀlightꢀoutput
•ꢀ Noꢀannoyingꢀlineꢀfrequencyꢀflickerꢀ
TheꢀMOSFETꢀwithinꢀU1,ꢀdiodeꢀD3,ꢀinductorꢀL2ꢀandꢀcapacitorꢀ
C3ꢀformꢀtheꢀbuckꢀconverterꢀstage.ꢀꢀTheꢀcontrollerꢀwithinꢀ
U1ꢀregulatesꢀtheꢀoutputꢀcurrentꢀbyꢀenablingꢀandꢀdisablingꢀ
MOSFETꢀswitchingꢀcycles.
•ꢀ Universalꢀinputꢀvoltageꢀrangeꢀ
•ꢀ Aꢀsingleꢀdesignꢀcanꢀbeꢀsoldꢀworldwide
•ꢀ Consistentlyꢀhighꢀefficiencyꢀacrossꢀentireꢀrange
•ꢀ MeetsꢀEN55022ꢀBꢀconductedꢀEMIꢀlimits
•ꢀ Completeꢀovervoltageꢀandꢀoverꢀtemperatureꢀprotection
•ꢀ Operatesꢀunloaded:ꢀcanꢀbeꢀtestedꢀwithoutꢀtheꢀLEDs
•ꢀ Auto-restart:ꢀwithstandsꢀshortedꢀoutputꢀindefinitely
•ꢀ Thermalꢀshutdown:ꢀprotectsꢀentireꢀlampꢀassembly
Duringꢀ normalꢀ operation,ꢀ theꢀ outputꢀ currentꢀ developsꢀ aꢀ
voltageꢀdropꢀacrossꢀR8ꢀandꢀR10,ꢀwhichꢀisꢀimpressedꢀacrossꢀ
C6.ꢀꢀWhenꢀtheꢀvoltageꢀacrossꢀC6ꢀexceedsꢀtheꢀVBEꢀofꢀQ1,ꢀ
Q1ꢀandꢀQ2ꢀbothꢀturnꢀon.ꢀꢀWhenꢀQ2ꢀturnsꢀon,ꢀcurrentꢀisꢀ
injectedꢀintoꢀtheꢀFEEDBACKꢀ(FB)ꢀpinꢀofꢀU1ꢀfromꢀC5,ꢀviaꢀ
R3.ꢀꢀWheneverꢀtheꢀcurrentꢀintoꢀtheꢀFBꢀpinꢀexceedsꢀ49ꢀmA,ꢀ
MOSFETꢀswitchingꢀisꢀdisabled.ꢀꢀTheꢀcontrollerꢀadjustsꢀtheꢀ
ratioꢀofꢀenabledꢀandꢀdisabledꢀcyclesꢀtoꢀregulateꢀtheꢀoutputꢀ
currentꢀatꢀ330ꢀmA.
Operation
Theꢀ non-isolatedꢀ buckꢀ converterꢀ shownꢀ inꢀ Figureꢀ 1ꢀ wasꢀ
designedꢀaroundꢀaꢀmemberꢀofꢀtheꢀLinkSwitch-TNꢀICꢀfamily,ꢀ
theꢀ LNK306DNꢀ (U1).ꢀAꢀ LNK306ꢀ wasꢀ selectedꢀ sinceꢀ itsꢀ
minimumꢀcurrentꢀlimitꢀ(450ꢀmA)ꢀensuresꢀthatꢀitꢀwillꢀbeꢀableꢀ
toꢀdeliverꢀtheꢀrequiredꢀ330ꢀmAꢀofꢀoutputꢀcurrent.
Duringꢀno-loadꢀoperation,ꢀtheꢀoutputꢀvoltageꢀisꢀsensedꢀbyꢀ
D1,ꢀD2ꢀandꢀC2.ꢀꢀTheꢀvoltageꢀacrossꢀC5ꢀfeedsꢀcurrentꢀintoꢀ
theꢀFBꢀpinꢀofꢀU1ꢀthroughꢀdividerꢀR7ꢀandꢀR1.ꢀꢀTheꢀFBꢀpinꢀ
D1
D2
R7
30 kΩ
BAV21WS-7-F BAV21WS-7-F
Q2
MMST3906
C5
100 nF
25 V
R3
10 kΩ
R6
10 kΩ
R1
4.7 kΩ
R4
10 kΩ
R9
4.7 kΩ
Q1
MMST3904
C4
100 nF
25 V
BP
C6
100 nF
25 V
9-15 V,
300 mA
FB
S
D
J3
L2
BR1
MB6S
600 V
R8
1 mH
RF1
10 Ω
2.5 W
2 Ω
LinkSwitch-TN
U1
LNK306DN
L
R10
R11
1 kΩ
C1
4.7 µF
380 V
C2
C3
2.2 µF
25 V
12 Ω
4.7 µF
85-265
VAC
D3
MURS160T3
380 V
L1
1 mH
N
J4
PI-4575-030707
Figure 1. 3 W LED, Halogen Bulb Replacement using LinkSwitch-TN in Non-Isolated Buck Converter Technology.
March 2007
DI-131
POWERINT [ Power Integrations ]
