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參數(shù)資料
| 型號： | ZXLD1100 |
| 文件頁數(shù)： | 8/15頁 |
| 文件大小： | 222K |
| 代理商： | ZXLD1100 |
APPLICATIONS
Programming the maximum LED current
The maximum LED currentis programmed by adding a
single resistorin series with the LED chain. The current
is determined by the resistor value and feedback
voltage and is given by:
I
LED
= V
FB
/R1
where V
FB
=100mV
The table below gives recommended resistor values
for required LED currents:
LED Current
R1 V alue
10mA
10
15mA
6.8
20mA
5
30mA
3.3
Dimming Control via a PWM signal on the EN pin
A Pulse Width Modulated (PWM) signal can be applied
to the EN pin in order to adjust the output current to a
value below the maximum LED current. Two modes of
adjustment are possible as described below.
True Analog Dimming - Filtered ‘DC’ mode
If a PWM signal of 10kHz or higher is applied to the EN
pin, the device will remain active when the EN pin is
low. However, the input to the internal low pass filter
will be switched alternately from V
to ground, with a
duty cycle (D) corresponding to thatofthe PWM signal.
This will present a filtered dc voltage equal to the duty
cycle multiplied by V
to the control loop and will
produce a dc output current lower than the maximum
set value. This current is given by:
I
OUTdc
= 0.1D/R1
This mode of adjustment minimizes flicker in the light
output and system noise.
Pulsed Dimming - Gated Mode
If a lower frequency of 1kHz or less is applied to the EN
pin, the device will be gated ‘on’ and ‘off’ ata duty cycle
(D) corresponding to that of the input signal. The
average output current is then given by:
I
OUTavg
0.1D/R1
This mode may be preferred over dc current control if
the purest white output is required. However, note the
120 s nominal turn-offdelay ofthe device, when using
the device in this mode.
Dimming Control using a DC voltage
For applications where the EN pin is not available a DC
voltage can be used to control dimming. By adding
resistors R2 and R3 and applying a DC voltage, the LED
current can be adjusted from 100% to 0%. As the DC
voltageincreases, thevoltagedropacross R2increases
and the voltage drop across R1 decreases, thus
reducing the current through the LEDs. Selection of R2
and R3 should ensure that the current from the DC
voltage is much less than the LED current and much
larger than the feedback current. The component
values in the diagram below represent 0% to 100%
dimming control from a 0 to 2V DC voltage.
Dimming Control using a logic signal
For applications where the LED current needs to be
adjusted in discrete steps a logic signal can be applied
as shown in the diagram below. When Q1 os ‘off’, R1
sets theminimum LED current.WhenQ1is ‘on’, R2sets
the LED currentthatwill be added to the minimum LED
current. The formula for selecting values for R1 and R2
are given below:
MOSFET ‘off’
I
V
R
LED MIN
(
FB
LED
)
MOSFET ‘on’
I
V
R
I
LED MAX
(
LED
LED MIN
(
FB
)
)
where V
FB
= 100mV
ZXLD1100
S E M IC O N D U C T O R S
ISSUE 2 - FEBRUARY 2004
8
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| ZXLD1100H6 | 制造商:Diodes Incorporated 功能描述:LED DRIVER ADJUSTABLE SMD SC-70-6 |
| ZXLD1100H6 | 制造商:Diodes Incorporated 功能描述:LED DRIVER ADJUSTABLE SMD SC-70-6 |
| ZXLD1100H6TA | 功能描述:LED照明驅(qū)動器 Series/Parallel RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SO-16N |
| ZXLD1100H6TC | 制造商:ZETEX 制造商全稱:ZETEX 功能描述:ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH AND OPEN CIRCUIT PROTECTION IN SC70-6 |
| ZXLD1101 | 制造商:ZETEX 制造商全稱:ZETEX 功能描述:ADJUSTABLE LED DRIVER WITH INTERNAL SWITCH IN TSOT23-5 |
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