Diodes AP3019A Manuel d'utilisateur télécharger pdf (Page 11)

Data Sheet

WHITE LED STEP-UP CONVERTER AP3019A

May. 2010 Rev. 1.8 BCD Semiconductor Manufacturing Limited

Application Information (Continued)

(2) Changing the Effective Feedback Voltage

There are three 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 Figure 21.

Figure 21. 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.

Figure 22. Dimming Control Using a Filtered PWM

Voltage

Third, using a logic signal to change the feedback

voltage. For example, the FB pin is connected to the

GND through a MOSFET and a resistor. And this

MOSFET is controlled a logic signal. The luminous

intensity of LEDs will be changed when the

MOSFET turns on or off.

Figure 23. Dimming Control Using Logic Signal

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Diodes AP3019A Manuel d'utilisateur Page 11