uses
TNY253ꢀforꢀimplementingꢀa
TVꢀstandbyꢀsupply.ꢀTheꢀcircuitꢀ
TNY253/254/255
V
EN
CLOCK
V
0 V
IN
DC
MAX
I
DRAIN
V
DRAIN
0 V
0
.2
.4
.6
.8
1
Time (ms)
V
DRAIN
Figure 7. TinySwitch Power-Up Timing Diagram.
PI-2261-061198
V
IN
Figure 6. TinySwitch Operation at Light Load.
BYPASS Pin Capacitor
12 V
TheꢀBYPASSꢀpinꢀusesꢀaꢀsmallꢀ0.1ꢀµFꢀceramicꢀcapacitorꢀforꢀ
decouplingꢀtheꢀinternalꢀpowerꢀsupplyꢀofꢀtheꢀTinySwitch.
0 V
Application Examples
V
DRAIN
Television Standby
12 V
0 V
500
TinySwitchꢀisꢀanꢀidealꢀsolutionꢀforꢀlowꢀcost,ꢀhighꢀefficiencyꢀ
standbyꢀpowerꢀsuppliesꢀusedꢀinꢀconsumerꢀelectronicꢀproductsꢀ
suchꢀasꢀTVs.ꢀꢀFigureꢀ9ꢀshowsꢀaꢀ7.5ꢀV,ꢀ1.3ꢀWꢀflybackꢀcircuitꢀthatꢀ
0
100
200
Time (ms)
Figure 8. TinySwitch Power Down Timing Diagram.
300
400
operatesꢀfromꢀtheꢀDCꢀhigh-voltageꢀalreadyꢀavailableꢀfromꢀtheꢀ
mainꢀpowerꢀsupply.ꢀꢀThisꢀinputꢀvoltageꢀcanꢀrangeꢀfromꢀ120ꢀtoꢀ
375ꢀVDCꢀdependingꢀonꢀtheꢀinputꢀACꢀvoltageꢀrangeꢀthatꢀtheꢀTVꢀ
isꢀratedꢀfor.ꢀꢀCapacitorꢀC1ꢀfiltersꢀtheꢀhigh-voltageꢀDCꢀsupply,ꢀ
andꢀisꢀnecessaryꢀonlyꢀifꢀthereꢀisꢀaꢀlongꢀtraceꢀlengthꢀfromꢀtheꢀ
sourceꢀofꢀtheꢀDCꢀsupplyꢀtoꢀtheꢀinputsꢀofꢀtheꢀTVꢀstandbyꢀcircuit.ꢀ
Theꢀhigh-voltageꢀDCꢀbusꢀisꢀappliedꢀtoꢀtheꢀseriesꢀcombinationꢀ
ofꢀtheꢀprimaryꢀwindingꢀofꢀT1ꢀandꢀtheꢀintegratedꢀhigh-voltageꢀ
MOSFETꢀinsideꢀtheꢀTNY253.ꢀꢀTheꢀlowꢀoperatingꢀfrequencyꢀofꢀ
theꢀTNY253ꢀ(44ꢀkHz),ꢀallowsꢀaꢀlowꢀcostꢀsnubberꢀcircuitꢀC2ꢀandꢀ
R1ꢀtoꢀbeꢀusedꢀinꢀplaceꢀofꢀaꢀprimaryꢀclampꢀcircuit.ꢀꢀInꢀadditionꢀ
toꢀlimitingꢀtheꢀDRAINꢀturnꢀoffꢀvoltageꢀspikeꢀtoꢀaꢀsafeꢀvalue,ꢀ
theꢀRCꢀsnubberꢀalsoꢀreducesꢀradiatedꢀvideoꢀnoiseꢀbyꢀloweringꢀ
theꢀdv/dtꢀofꢀtheꢀDRAINꢀwaveform,ꢀwhichꢀisꢀcriticalꢀforꢀvideoꢀ
applicationsꢀsuchꢀasꢀTVꢀandꢀVCR.ꢀꢀOnꢀfixedꢀfrequencyꢀPWMꢀ
andꢀRCCꢀcircuits,ꢀuseꢀofꢀaꢀsnubberꢀwillꢀresultꢀinꢀanꢀundesir-
ableꢀfixedꢀACꢀswitchingꢀlossꢀthatꢀisꢀindependentꢀofꢀload.ꢀꢀTheꢀ
ON/OFFꢀcontrolꢀonꢀtheꢀTinySwitchꢀeliminatesꢀthisꢀproblemꢀ
byꢀscalingꢀtheꢀeffectiveꢀswitchingꢀfrequencyꢀandꢀtherefore,ꢀ
switchingꢀlossꢀlinearlyꢀwithꢀload.ꢀꢀThusꢀtheꢀefficiencyꢀofꢀtheꢀ
supplyꢀstaysꢀrelativelyꢀconstantꢀdownꢀtoꢀaꢀfractionꢀofꢀaꢀwattꢀofꢀ
outputꢀloading.
TheꢀsecondaryꢀwindingꢀisꢀrectifiedꢀandꢀfilteredꢀbyꢀD1ꢀandꢀC4ꢀtoꢀ
createꢀtheꢀ7.5ꢀVꢀoutput.ꢀꢀL1ꢀandꢀC5ꢀprovideꢀadditionalꢀfiltering.ꢀ
Theꢀoutputꢀvoltageꢀisꢀdeterminedꢀbyꢀtheꢀsumꢀofꢀtheꢀoptocouplerꢀ
U2ꢀLEDꢀforwardꢀdropꢀ(~ꢀ1ꢀV)ꢀandꢀZenerꢀdiodeꢀVR1ꢀvoltage.ꢀ
TheꢀresistorꢀR2,ꢀmaintainsꢀaꢀbiasꢀcurrentꢀthroughꢀtheꢀZenerꢀtoꢀ
improveꢀitsꢀvoltageꢀtolerance.
10 W Standby
TheꢀTNY255ꢀisꢀidealꢀforꢀstandbyꢀapplicationsꢀthatꢀrequireꢀupꢀ
toꢀ10ꢀWꢀofꢀpowerꢀfromꢀ230ꢀVACꢀorꢀ100/115ꢀVACꢀwithꢀdoublerꢀ
circuit.ꢀꢀTheꢀTNY255ꢀoperatesꢀatꢀ130ꢀkHzꢀasꢀopposedꢀtoꢀ44ꢀkHzꢀ
forꢀTNY253/254.ꢀꢀTheꢀhigherꢀfrequencyꢀoperationꢀallowsꢀtheꢀ
Rev E
02/12
5
POWERINT [ Power Integrations ]
