AME, Inc.
AME5142
n
Application Hints
Dimming Control
B. Using a DC Voltage
Using a variable DC voltage to adjust the brightness
is a popular method in some applications. The dim-
ming control using a DC voltage circuit is shown in
Figure 6. According to the Superposition Theorem,
as the DC voltage increases, the voltage contributed
to V
FB
increases and the voltage drop on R2 decreases,
i.e. the LED current decreases. For example, if the
V
DC
range is from 0V to 3V, the selection of resistors
in Figure 6 sets dimming control of LED current from
20mA to 0mA.
L1
10µH
V
OUT
IN
SW
C
OUT
1µF
GND
FB
R4
91K
R
DC
10K
3V
C
DC
0.1µF
R2
7.5Ω
White LED Boost Converter
In Tiny Package
C. Using a Filtered PWM Signal
The filtered PWM signal can be considered as an adjust-
able DC voltage. It can be used to replace the variable DC
voltage source in dimming control. The circuit is shown in
Figure 7.
L1
10µH
V
OUT
IN
SW
C
OUT
1µF
V
IN
2.7V to 5.5V
C
IN
4.7µF
EN
AME5142
OVP
R3
5.1K
V
IN
2.7V to 5.5V
C
IN
4.7µF
EN
AME5142
OVP
R3
5.1K
GND
FB
R4
91K
VDC Dimming
0V to 3V
R2
7.5Ω
0V
PWM Signal
Figure 7. Dimming Control Using a Filtered PWM Signal
Figure6. Dimming Control Using a DC Voltage
10
Rev. A.01
AME [ ANALOG MICROELECTRONICS ]
