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HT7L4091 Folha de dados(PDF) 7 Page - Holtek Semiconductor Inc

Nome de Peças HT7L4091
Descrição Electrónicos  Universal Step-Down PWM Control For High Brightness LED Lighting Control
PDF  17 Pages
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Fabricante Electrônico  HOLTEK [Holtek Semiconductor Inc]
Página de início  http://www.holtek.com
Logo HOLTEK - Holtek Semiconductor Inc

HT7L4091 Folha de dados(HTML) 7 Page - Holtek Semiconductor Inc

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Rev. 1.20
7
March 12, 2013
HT7L4091
Tcharge
Tdischarge
t
VIN
8.333ms
1
120Hz
ΔV
The Waveform of Input Voltage in the C1
Chargeperiod:
ms
f
T
AC
CP
333
.
8
2
1
=
×
=
∆
−
−
×
=
−
90
)
1
(
sin
1
2
1
arg
IN
CP
e
ch
V
V
T
T
,where
%
DCripple
IN
V
V
V
∆
=
∆
Tdischarge=TCP–Tcharge
ms
ms
ms
T
e
dich
2232
.
6
90
%)
30
1
(
sin
1
2
333
.
8
333
.
8
1
arg
=
−
−
×
−
=
−
Application Description
Thissectionshowshowtodesignabuckcircuit
LEDapplicationusingasimpleexample.Forother
application conditions, such as high efficiency
solutions,refertotheHT7L4091applicationnotesfor
moredetails.
Forexample:
AC Input voltage: VAC_typ = 110Vrms; VAC_min = 95Vrms;
VAC_max = 125Vrms; fAC = 60Hz
Target working condition: FPWM > 40kHz
Output Voltage: LED string × LED Voltage = 8×(3~3.3)
= 24V~26.4V, typical 25.2V
Average Output LED Current: ILED = 400mA
Expected efficiency: η = 90%
Refertothetypicalapplicationcircuit.
Input Bulk Capacitor – C1
The input Bulk Capacitor determines the ripple
amplitudeofinputvoltageafterrectification.Alarge
capacitancegeneratesasmallerinputvoltageripple
amplitude.Thefirstdesigncriteriontomeetisthat
themaximumLEDstringvoltageshouldbelessthan
80%oftheminimumACinputvoltage(Vmin,AC).Note
that80%isaroughestimatehere.Herethelarge
rippleamplitudehasawidefrequencyvariationwhich
leadstoincreaseincircuitpowerlosses.Assumethat
theinputvoltageDCripple(ΔVDCripple%)isequalto
30%andthencalculatetheC1value.
V
V
V
V
DCripple
AC_
4
.
26
2
.
75
8
.
0
%)
30
1
(
95
2
8
.
0
%)
1
(
2
min
>
=
×
−
×
×
=
×
∆
−
×
×
(maximum output voltage)
Aboveformulameans30%inputvoltagerippleis
approvedthatexceedoutputvoltage.
Finally,ausefulrulecanfindthevalleyvoltageofthe
inputvoltage.Usingthefigurebelow,itisnecessary
tocalculatethechargetimeanddischargetimeofthe
inputbulkcapacitor.



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