AP5724

WHITE LED STEP-UP CONVERTER

AP5724

Document number: DS31843 Rev. 3 - 2

11 of 17

www.diodes.com

July 2010

© Diodes Incorporated

2. Using a DC Voltage

For some applications, the preferred method of brightness control is a variable DC voltage to adjust the

LED current. The dimming control using a DC voltage is shown in Figure 3. As the DC voltage increases, the

selection of R2 and R3 will make the current from the variable DC source much smaller than the LED current and

dimming control of LED current from 0mA to 20mA.

AP5724

FB

5

R2

5k

R3

100k

Figure 3. Dimming Control Using a DC Voltage

3. Using a Filtered PWM Signal

The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable

DC voltage source in dimming control.

4. Using a Logic Signal

For applications that need to adjust the LED current in discrete steps, a logic signal can be used as shown in

increases when the NMOS is turned on.

AP5724

FB

Logic

Signal

Figure 4. Dimming Control Using a Logic Signal