AL5802

Document number: DS35516 Rev. 9 - 2

7 of 11

www.diodes.com

March 2014

© Diodes Incorporated

AL5802

Application Information

Fig. 14 Typical Application Circuit for

Linear Mode Current Sink LED Driver

Fig. 15 Application Circuit for Increasing LED Current

The AL5802 has been designed for driving low current LEDs with typical

LED current of 20mA to 100mA. It provides a cost effective way for

driving low current LEDs compared with more complex switching

regulator solutions. Furthermore, it reduces the PCB board area of the

solution as there is no need for external components like inductors,

capacitors and switching diodes.

Figure 14 shows a typical application circuit diagram for driving an LED

or string of LEDs. The NPN transistor Q1 measures the LED current by

into Q2. Q2 operates in linear mode to regulate the LED current. The

LED current is

From this, for any required LED current the necessary external resistor

Two or more AL5802 can be connected in parallel to construct higher

current LED strings as shown in Figure 15.

Consideration of the expected linear mode power dissipation must be

factored into the design, with respect to the AL5802's thermal

resistance. The maximum voltage across the device can be calculated

by taking the maximum supply voltage less the voltage across the LED

string.

As the output current of AL5802 increases, it is necessary to provide

appropriate thermal relief to the device. The power dissipation

supported by the device is dependent upon the PCB board material, the

copper area and the ambient temperature. The maximum dissipation

the device can handle is given by:

Refer to the thermal characteristic graphs on page 4 for selecting the

appropriate PCB copper area.