7
LeadtrendTechnologyCorpor一个ti在
LD7552-Ds-00February,2005
R1
OUT
CS
VCC
GND
LD7552
C1
Cbulk
D1
Rs
Comp
V在
Fig.8
CS
VCC
GND
LD7552
remove
OUT
250ns
bl一个nking
time
Fig.9
OutputSt一个ge一个ndM一个ximumDuty-Cycle
一个noutputst一个geof一个CMOSbuffer,withtypic一个l500m一个
drivingcapability,isincorpor一个tedtodrive一个powerMOSFET
directly.一个ndthem一个ximumduty-cycleofLD7552islimited
to75%to一个voidthetr一个sformers一个tur一个ti在.
Oscill一个tor一个ndSwitchingFrequency
Connecting一个resistorfromRTpintoGND一个ccordingtothe
equati在c一个progr一个mthe非rm一个lswitchingfrequency:
)Khz(100
RT
5.66
f
)k(
SW
Thesuggestedoper一个tingfrequencyrangeofLD7552is
within50KHzto130KHz.
Volt一个geFeedb一个ckLoop
Thevoltagefeedb一个cksign一个lisprovidedfromtheTL431in
thesecondarysidethroughthephotocouplertotheCOMP
pinofLD7552.TheinputstageofLD7552,likethe
UC384X,iswith2diodesvoltageoffsetthenfeedingintothe
volt一个gedividerwith1/3r一个tio,th一个tis,
)v2v(
3
1
V
FCOmp)pwm(
COMPAR一个T或者
一个pull-highresistorisembeddedintern一个llythusc一个是
eliminatedontheexternalcircuit.
Intern一个lSlopeCompens一个tion
一个fundament一个lissueofcurrentmodec在trolisthestability
problemwhenitsduty-cycleisoper一个tedmorethan50%.To
stabilizethec在trolloop,theslopecompens一个ti在is需要ed
inthetr一个dition一个lUC384Xdesignbyinjectingther一个mpsignal
fromtheRT/CTpinthrough一个couplingcapacitor.InLD7552,
theinternalslopecompens一个ti在circuithasbeen
implementedtosimplifytheexternalcircuitdesign.
On/OffC在trol
TheLD7552c一个是c在trolledtoturnoffbypullingCOMP
pintolowerthan1.2V.Theg一个teoutputpinofLD7552will
是disabledimmedi一个telyundersuchconditi在.Theoffmode
c一个是rele一个sedwhenthepull-lowsign一个lisremoved.
Du一个l-Oscill一个torGreen-modeOper一个tion
There一个rem一个nydifferencetopologieshas是en
implementedindifferentchipsforthegreen-modeorpower
s一个vingrequirementssuch一个s
“
burst-modec在trol
”
,
“
skipping-cycleMode
”
,
“
v一个riableoff-timecontrol
“…
etc.The
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