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參數(shù)資料
| 型號： | HV9903 |
| 廠商： | Supertex, Inc. |
| 元件分類： | LED驅(qū)動器 |
| 英文描述： | White LED Driver |
| 中文描述： | 白光LED驅(qū)動器 |
| 文件頁數(shù)： | 7/12頁 |
| 文件大?。?/td> | 326K |
| 代理商： | HV9903 |
Diode Selection
Since the HV9903 operates at a 1.2MHz switching
frequency, the output rectifier must be fast – 20ns or
less. The faster the diode, the more efficiently the
driver operates. Also, choose a diode with low
capacitance to improve performance. A Schottkey
need not be used, although its lower forward voltage
drop improves efficiency. Peak current rating is the
same as for the inductor. Average current is simply
the LED current. To be compatible with the HV9903’s
open LED protection, the diode’s reverse voltage
rating should be 35V or more. Otherwise, the diode’s
voltage rating should be greater than the LED string’s
voltage drop plus 1 volt.
Dimming
Dimming may be accomplished in one of two ways:
DC dimming or PWM dimming. DC dimming linearly
regulates the current through the LEDs in a
continuous fashion, while PWM dimming rapidly turns
the LEDs on and off while maintaining a constant ‘on’
current. In PWM dimming, the ratio of on to off time
determines perceived brightness. The on/off
frequency must be high enough to prevent visible
flickering – typically above 70Hz. The claimed
advantage of PWM dimming is less color shift as the
LED is dimmed, although the effect is virtually
imperceptible.
DC dimming is accomplished by applying a bias to the
R
SET
resistor.
DC Dimming
R
BIAS
BIAS
DIM
V
SET
LED
I
R
R
100mV
100mV
225
1
6
5
4
2
3
SW
GND
LED
R
SET
SHDN
V
DD
HV9903
L
D
C
OUT
C
DD
R
SET
V
DD
Shutdown
V
DIM
DC Dimming Frequency Response
100
1k
10k
100k
-50
I
L
R
Frequency (Hz)
-40
-30
-20
-10
0
+10
PWM dimming may be implemented via the SHDN
input or via R
SET
. Since SHDN reactivates soft-start, a
delay is introduced (~1ms) to LED turn-on. For this
reason, it is better to use the R
SET
pin for PWM
dimming, as it does not include the soft-start delay.
PWM dimming frequency should be in the range of
70-100Hz to minimize the effect of turn-on delays
while avoiding flicker.
PWM Dimming via SHDN
1
6
5
4
2
3
SW
GND
LED
R
SET
SHDN
V
DD
HV9903
L
D
C
OUT
C
DD
R
SET
V
DD
PWM
SET
avg
LED
R
D
I
V
5
22
)
(
HV9903
HV9903
7
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| HV9903DB1 | 制造商:Supertex Inc 功能描述: |
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