Diodes AP3033 - Manual (Page 10)

Preliminary Datasheet
10
Jan. 2010 Rev. 1. 0 BCD Semiconductor Manufacturing Limited
WHITE LED STEP-UP CONVERTER AP3033
Application Information (Continued)
Two other typical types of dimming control circuit are
presented as below.
(1) Using DC Voltage to Change the Effective Feed-
back Voltage
Adding a constant DC voltage through a resistor
divider to FB pin can control the dimming. Changing
the DC voltage or resistor between the FB Pin and the
DC voltage can get appropriate luminous intensity.
Comparing with all kinds of PWM signal control, this
method features a stable output voltage and LEDs
current. Please refer to Figure 15.
Figure 15. Dimming Control
Using DC Voltage
(2) Using Filtered PWM Signal to Change the Effec-
tive Feedback Voltage
The filtered PWM signal can be considered as a
varying and adjustable DC voltage, please refer to Fig-
ure 16.
Figure 16. Dimming Control
Using Filtered PWM Voltage
R1
R2 R3
PWM
R4
C
Effective
Feedback Voltage
FB
AP3033
R1
FB
AP3033
R2 R3
V
DC
Effective
Feedback Voltage