Diodes AP3032 - Manual (Page 10)

Data Sheet
WHITE LED STEP-UP CONVERTER AP3032
Dec. 2012 Rev. 1. 2 BCD Semiconductor Manufacturing Limited
10
Application Information (Continued)
Two typical types of dimming control circuit are
present as below. First, controlling CTRL Pin voltage
to change operation state is a good choice. Second,
changing the feedback voltage to get appropriate duty
and luminous intensity is also useful.
5.1 Adding a Control Signal to CTRL Pin
Adding a PWM signal to CTRL pin directly, the
AP3032 is turned on and off by this signal. When the
PWM frequency is lower than 2.5kHz (Typ), the IC
works in the soft-start mode to dimming the light. But
we intense suggest set the PWM signal frequency
higher than 25kHz to avoid audio noise. In this
situation, IC works in the standby mode and start
directly to achieve dimming the light. More details
please refer to Figure 17 and Figure 18.
AP3032
CTRL
up to 25kHz
Figure 17. Dimming Control
Using a PWM Signal on CTRL Pin
Figure 18. High Frequency
(25kHz) Dimming Waveform
5.2 Changing the Effective Feedback Voltage
There are two popular methods to change the
effective feedback voltage.
First, 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 19.
Figure 19. Dimming Control
Using DC Voltage
Second, using a filtered PWM signal can do it. The
filtered PWM signal can be considered as a varying
and adjustable DC voltage. Please refer to Figure 20.
Figure 20. Dimming Control
Using Filtered PWM Voltage