AL8807B Ver la hoja de datos (PDF) - Diodes Incorporated.

Número de pieza

componentes Descripción

Fabricante

AL8807B

HIGH EFFICIENCY 36V 1.3A PWM DIMMABLE BUCK LED DRIVER

Diodes Incorporated. 

AL8807B

Application Information

The AL8807B is a hysteretic (also known as equal ripple) LED driver with integrated power switch. It is available in two packages that provide a

PCB area-power dissipation capability compromise. It is recommended that at higher LED currents/smaller PCBs that the MSOP-8EP version is

used to maximize the allowable LED current over a wider ambient temperature range.

AL8807B Operation

In normal operation, when voltage is applied at +VIN, the AL8807B internal switch is turned on. Current starts to flow through sense resistor R1,

inductor L1, and the LEDs. The current ramps up linearly, and the ramp rate is determined by the input voltage +Vin and the inductor L1.

This rising current produces a voltage ramp across R1. The internal circuit of the AL8807B senses the voltage across R1 and applies a

proportional voltage to the input of the internal comparator.

When this voltage reaches an internally set upper threshold, the internal switch is turned off. The inductor current continues to flow through R1, L1,

the LEDs and the Schottky diode D1, and back to the supply rail, but it decays, with the rate of decay determined by the forward voltage drop of

the LEDs and the Schottky diode.

This decaying current produces a falling voltage at R1, which is sensed by the AL8807B. A voltage proportional to the sense voltage across R1 is

applied at the input of the internal comparator. When this voltage falls to the internally set lower threshold, the internal switch is turned on again.

This switch-on-and-off cycle continues to provide the average LED current set by the sense resistor R1.

LED Current Control

The LED current is controlled by the resistor R1 in Figure 31.

D1 R1

Ch4: LED Current

VIN:

6 ~ 36V

C1 AL8807B

PWM Dimming

Input:

C2

L1

VIN = 12V

TA =25ºC

2 LEDs

20ns/div

No C2

Ch2: 2V/div

Ch4: 100mA/div

Ch2: SW Pin

Figure 31 Typical Application Circuit

Figure 32 Typical Operating Waveform (C2 not fitted)

Connected between VIN and SET the nominal average output current in the LED(s) is defined as:

ILED



VTHD

R1

For example for a desired LED current of 660mA and a default voltage VCTRL=2.5V the resulting resistor is:

R1



VTHD

ILED



0.1

0.66

 150m

AL88070B

Document number: DS36191 Rev. 1 - 2

9 of 18

www.diodes.com

March 2014

© Diodes Incorporated

Share Link: