AME, Inc.
White LED Boost Converter
In Tiny Package
AME5142
n Application Hints
Dimming Control
B. Using a DC Voltage
C. Using a Filtered PWM Signal
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 VFB increases and the voltage drop on R2 decreases,
i.e. the LED current decreases. For example, if the
VDC range is from 0V to 3V, the selection of resistors
in Figure 6 sets dimming control of LED current from
20mA to 0mA.
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
10mH
VIN 2.7V to 5.5V
VOUT
CIN
4.7mF
COUT
1mF
IN
SW
L1
AME5142OVP
EN
10mH
VIN 2.7V to 5.5V
VOUT
R3
5.1K
CIN
4.7mF
COUT
1mF
FB
GND
IN
SW
R4
R2
7.5W
91K
AME5142OVP
EN
CDC
0.1mF
RDC
10K
R3
5.1K
3V
0V
FB
GND
R2
7.5W
PWM Signal
R4
91K
Figure 7. Dimming Control Using a Filtered PWM Signal
VDC Dimming
0V to 3V
Figure6.Dimming Control Using a DC Voltage
Rev.A.01
10
AME [ ANALOG MICROELECTRONICS ]
