AL8808EV1

Issue 1 – January 2013

www.diodes.com

© Diodes Incorporated 2013

5

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 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 30V supply and one LED, the switching frequency is typically 188kHz. The efficiency level is

>85%.

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.