AL8807EV4

Issue 2 – May 2012

© Diodes Incorporated 2012

www.diodes.com

7 of 8

Current Setting

parallel.

For the schematic values this gives a resistance of 0.15 * 0.2 (0.15 + 0.2) = 0.0857 ohms.

For the schematic values this gives an LED current of 0.1/0.0857 = 1.167 A nominally. In practice

there is a slight reduction in current partly due to the resistance of the PCB copper, depending on the

PCB layout. At 1.1A this reduction is typically about 5% using AL8807EV4.

The following table gives commercially available resistor values for typical current requirements,

allowing a current error of 3% maximum not including the effect of PCB copper. A power limit of

125mW is assumed for the 0805 size resistors with 50% de-rating.

LED Current

R1, ohms

R2, ohms

150mA

0.68

DO NOT FIT

300mA

0.33

DO NOT FIT

380mA

0.51

DO NOT FIT

500mA

0.2

DO NOT FIT

660mA

0.15

DO NOT FIT

1A

0.2

0.2

1.1A

0.15

0.2

Performance

The performance of the AL8807EV4 demonstrated shows the capability to regulate LED current. The

LED current of 1.1A is approximately 5% lower than the calculated value. This is partly due to copper

resistance. With a load of 2 LEDs, the current changes by less than ±2% over the input voltage range

from 9VDC to 30VDC. With 2 LEDs and a supply of 12VDC, the switching frequency is approximately

440kHz.

For further advice, please contact your local Diodes Field Applications Engineer, or one of our

sales offices listed on the back page of this document.