EUP2584
Constant Output Voltage for Backlight of Main
Panel and Flashlight
Constant Output Voltage for Backlight of Main
Panel and Keypad
Figure 6 is an application of EUP2584 for backlight of
main panel and flashlight. Setting the divider-resistors
(R1 & R2) is to get a constant output voltage that
depends on the forward voltage and the numbers of
series-LEDs. There are three kinds of mode controlled
by the switches - backlight mode /flashlight mode
/backlight + flashlight mode. It can turn on backlight or
flashlight at one time or both at the same time.
Applying different duty cycle of PWM signal above
22kHz to backlight's switch can also control the
brightness. The following formula (2)(3) can determine
R3 and R4.
Figure 7 is another application of EUP2584 for
backlight and keypad. Setting the divider-resistors (R1
& R2) is to get a constant output voltage that depends
on the forward voltage and the numbers of series-LEDs.
It can turn on backlight of main panel and keypad at
the same time. Applying different duty cycle of PWM
signal above 22kHz to the backlight's switch can also
control the brightness of main panel's backlight. The
keypad's backlight will keep the same brightness
during the dimming control of main panel. Otherwise
the brightness of keypad's s backlight can also change
during the dimming control of main panel by using the
application circuit as figure 4. The following formula
(5)(6) can determine the resistors of Figure 8.
V
− 3VFb − V
OUT
DS
R3 =
R4 =
--------------------------(2)
--------------------------(3)
Ib
V
− 3VFb − V
OUT
DS
V
− 3VFf − V
R3 =
----------------------------(5)
OUT
DS
Ib
If
V
−3VFk
V
= Ib×R
---------------------------------(4)
DS(ON)
OUT
DS
R4 = R5 = R6 =
= Ib×R
----------------------(6)
Ik
----------------------------------(7)
DS(ON)
V
DS
Figure 6. Constant Output Voltage for Backlight and Flashlight
Figure 7. Constant Output Voltage for Backlight and Keypad
DS2584 Ver1.1 Mar. 2008
10
EUTECH [ EUTECH MICROELECTRONICS INC ]
