AL9910/AL9910A/AL9910-5

UNIVERSAL HIGH VOLTAGE HIGH BRIGHTNESS LED DRIVER

AL9910/AL9910A/AL9910-5

Document number: DS35103 Rev. 7 - 2

7 of 16

www.diodes.com

February 2012

© Diodes Incorporated

Applications Information

The AL9910 is very versatile and is capable of operating in isolated or non-isolated topologies. It can also be made to operate

in continuous as well as discontinuous conduction mode.

Fig. 1 Functional Block Diagram

The AL9910 contains a high voltage LDO (see figure 1) the output of the LDO provides a power rail to the internal circuitry

In a non-isolated Buck LED driver when the gate pin goes high the external power MOSFET Q1 is turned on causing current

current sense pin threshold the external MOSFET Q1 is turned off. The stored energy in the inductor causes the current to

continue to flow through the LEDs via diode D1.

The AL9910’s LDO provides all power to the rest of the IC including Gate drive this removes the need for large high power

start-up resistors. This means that operate correctly it requires around 0.5mA from the high voltage power rail. The LDO can

also be used to supply up to 1mA to external circuits.

The AL9910 operates and regulates by limiting the peak current of the external MOSFET; the peak current sense threshold is

nominally set at 250mV.

The same basic operation is true for isolated topologies, however in these the energy stored in the transformer delivers

energy to LEDs during the off-cycle of the external MOSFET.

Design Parameters

Setting the LED Current

In the non-isolated buck converter topology, figure 1, the average LED current is not the peak current divided by 2 - however,

there is a certain error due to the difference between the peak and the average current in the inductor. The following equation

accounts for this error:

()

))

I

*

5

.

0

(

I

mV

250

R

RIPPLE

LED

SENSE

+

=

.

250mV

LD

V

DD

LDO

V

IN

OTP

PWM_D

GND

7.5/10V

OSC

S

RO

R

OSC

GATE

CS

100k

V

DD

V

IN

R

SENSE

AL9910/AL9910A

250mV

LD

V

DD

LDO

V

IN

OTP

PWM_D

GND

7.5/10V

OSC

S

RO

R

OSC

GATE

CS

100k

V

DD

V

IN

R

SENSE

AL9910/AL9910A