Design Idea DI-133
LinkSwitch®-XT
Non-isolated Induction Cooktop Auxiliary Supply
Application
Device
Power Output Input Voltage
5.9 W 185-265 VAC
Output Voltage
Topology
Induction Cooktop LNK364P
5 V, 100 mA / 18 V, 300 mA
Flyback
Design Highlights
Aꢀhigh-voltageꢀcurrentꢀsourceꢀwithinꢀU1ꢀfeedsꢀcurrentꢀintoꢀ
bypassꢀcapacitorꢀC3,ꢀduringꢀtheꢀMOSFETꢀoff-time.ꢀꢀCapacitorꢀ
C3ꢀdevelopsꢀtheꢀoperatingꢀvoltageꢀforꢀtheꢀICꢀandꢀsuppliesꢀ
theꢀnormalꢀoperatingꢀcurrentꢀtoꢀtheꢀchip.
•ꢀ Lowꢀcost,ꢀlowꢀcomponentꢀcountꢀsolution:ꢀonlyꢀ17ꢀparts
•ꢀ Bothꢀoutputsꢀexhibitꢀgoodꢀcrossꢀregulation
•ꢀ <130ꢀmWꢀno-loadꢀpowerꢀconsumptionꢀatꢀ265ꢀVAC
•ꢀ MeetsꢀCECꢀactiveꢀmodeꢀefficiencyꢀwithꢀgoodꢀmargin
DueꢀtoꢀtheꢀphasingꢀofꢀT1’sꢀwindingsꢀandꢀtheꢀlocationsꢀandꢀ
orientationsꢀofꢀtheꢀoutputꢀdiodesꢀ(D4ꢀandꢀD5),ꢀnoꢀsecondaryꢀ
currentꢀflowsꢀwhileꢀtheꢀMOSFETꢀisꢀonꢀandꢀcurrentꢀisꢀflowingꢀ
throughꢀtheꢀprimaryꢀwindingꢀofꢀT1.ꢀꢀOnceꢀtheꢀintegratedꢀ
controllerꢀwithinꢀU1ꢀswitchesꢀoffꢀtheꢀMOSFET,ꢀtheꢀvoltagesꢀ
acrossꢀtheꢀwindingsꢀofꢀT1ꢀreverse,ꢀD4ꢀandꢀD5ꢀareꢀforwardꢀ
biased,ꢀ andꢀ secondaryꢀ windingꢀ currentꢀ flowsꢀ intoꢀ outputꢀ
capacitorsꢀC4ꢀandꢀC5.
Operation
Theꢀnon-isolatedꢀflybackꢀconverterꢀshownꢀinꢀFigureꢀ1ꢀwasꢀ
designedꢀaroundꢀaꢀmemberꢀofꢀtheꢀLinkSwitch-XTꢀICꢀfamily,ꢀ
theꢀLNK364Pꢀ(U1).ꢀꢀItsꢀdualꢀoutputsꢀ(5ꢀVꢀforꢀtheꢀdisplayꢀandꢀ
18ꢀVꢀforꢀtheꢀfanꢀandꢀIGBTꢀcontrolꢀcircuit)ꢀcanꢀprovideꢀupꢀtoꢀ
5.9ꢀWꢀofꢀpowerꢀatꢀtheꢀlowestꢀinputꢀlineꢀvoltageꢀ(185ꢀVAC).
Resistorꢀ dividerꢀ R3ꢀ andꢀ R4ꢀ senseꢀ theꢀ 5ꢀ Vꢀ output.ꢀ ꢀ Theꢀ
controllerꢀwithinꢀU1ꢀusesꢀtheꢀcurrentꢀintoꢀtheꢀFEEDBACKꢀ
(FB)ꢀpinꢀtoꢀcontrolꢀMOSFETꢀswitchingꢀandꢀregulateꢀtheꢀ
5ꢀVꢀoutput.ꢀꢀTheꢀturnsꢀratioꢀbetweenꢀtheꢀ5ꢀVꢀandꢀtheꢀ18ꢀVꢀ
windingsꢀprovidesꢀadequateꢀregulationꢀofꢀtheꢀ18ꢀVꢀoutput.ꢀ
AnꢀLCꢀpostꢀfilterꢀ(L1ꢀandꢀC6)ꢀonꢀtheꢀ5ꢀVꢀoutputꢀattenuatesꢀ
theꢀswitchingꢀrippleꢀtoꢀ<100ꢀmVꢀpk-pk.
SinceꢀtheꢀcooktopꢀhasꢀconductedꢀEMIꢀfilteringꢀforꢀtheꢀinductionꢀ
heatingꢀconverter,ꢀthisꢀauxiliaryꢀsupplyꢀrequiresꢀnoꢀfuseꢀorꢀ
filterꢀcomponents.ꢀꢀDiodeꢀD1ꢀhalf-waveꢀrectifiesꢀtheꢀACꢀinputꢀ
andꢀcapacitorꢀC1ꢀfiltersꢀitꢀtoꢀproduceꢀtheꢀhigh-voltageꢀDCꢀbusꢀ
thatꢀfeedsꢀtransformerꢀT1.ꢀꢀAnꢀRCDꢀclampꢀ(C2,ꢀD3,ꢀR1ꢀandꢀ
R2)ꢀacrossꢀtheꢀprimaryꢀwindingꢀofꢀT1ꢀlimitsꢀtheꢀamplitudeꢀofꢀ
theꢀleakage-inductanceꢀvoltageꢀspikeꢀthatꢀoccursꢀeachꢀtimeꢀtheꢀ
integratedꢀpowerꢀMOSFETꢀwithinꢀU1ꢀswitchesꢀoff.
T1
L
+18 V, 300 mA
2
8
C2
1 nF
1 kV
D1
1N4007
D4
UF4002
R1
120 kΩ
C4
100 µF
25 V
L1
3
6
7
6.8 µH
+5 V, 100 mA
RTN
R2
100 Ω
C5
C6
100 µF
10 V
100 µF
10 V
5
D3
1N4007
C1
4.7 µF
400 V
185-265
VAC
EE16
D5
UF4002
R4
16 kΩ
1/8 W
LinkSwitch-XT
U1
D
LNK364P
FB
BP
R3
S
10 kΩ
C3
100 nF
50 V
1/8 W
N
PI-4573-020907
Figure 1. LinkSwitch-XT, 5.9 W Induction Cooktop, Auxiliary Power Supply.
February 2007
DI-133