AL8807EV3

Issue 1 – December 2011

www.diodes.com

© Diodes Incorporated 2011

5

AL8807EV3 Basic operation at full voltage

1.

Connect Vin and GND

Warning: The board does not feature reverse battery/supply protection.

2.

Set the PSU to 36V

3.

Turn on the PSU and the LED will illuminate and the current should be approximately 680mA.

Warning: Do not stare at the LED directly.

Switching the output current off

Shorting the CTRL pin to GND will cause the LED current to go to zero.

Soft start

Adding a C2 capacitor will create a soft-start power-up sequence (0.1ms/nF). This delay will reduce

the PWM dimming performance.

Changing the LED current

1.

Remove R1.

2.

Calculate and replace sense resistor, R1, the value of which is based on the required LED

current without dimming. R1 can be calculated using following equation :

R1 = the sense resistor value in ohms.

0.1V is the nominal sense voltage with ‘CTRL’ open circuit or set to 2.5V.

The device calculator at the address below can be used to speed up the redesign phase:

http://www.diodes.com/destools/calculators.html

PERFORMANCE

The system efficiency depends on the sense resistor, supply voltage, switching frequency and the

number of LEDs.

With a 12V supply and two LEDs, the switching frequency is typically 102kHz, and the efficiency level

is 88% .

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.