AL9910SP-13 Diodes Zetex, AL9910SP-13 Datasheet - Page 12

• Manufacturer Part Number: AL9910SP-13
• Manufacturer: Diodes Zetex

Specifications of AL9910SP-13

• Lead Free Status / Rohs Status: Compliant

Applications Information
DC-DC Buck LED driver
The design procedure for an ac input buck LED driver outlined in the previous chapters equally applies DC input LED drivers.
When driving long LED chains care should be taken not to induce SBO – maximum LED chain voltage should be less half of
V
DC-DC Boost LED driver
Due to the topology of the AL9910 LED driver-controller it is capable of being used in boost configurations – at reduced
accuracy. The accuracy can be improved by measuring the LED current with an op amp and use the op amp’s output to drive
the LD pin.
A Boost LED driver is used when the forward voltage drop of the LED string is higher than the input supply voltage. For
example, the Boost topology can be appropriate when input voltage is supplied by a 48V power supply and the LED string
consists of twenty HB LEDs, as the case may be for a street light.
In a Boost converter, when the external MOSFET is ON the energy is stored in the inductor which is then delivered to the
output when the external MOSFET switches OFF. If the energy stored in the inductor is not fully depleted by the next
switching cycle (continuous conduction mode) the DC conversion between input and output voltage is given by:
From the switching frequency, f
From this the required inductor value can be determined by:
The Boost topology LED driver requires an output capacitor to deliver current to the LED string during the time that the
external MOSFET is on.
In boost LED driver topologies if the LEDs should become open circuit damage may occur to the power switch and so some
form of detection should be present to provide Over-voltage detection/protection.
AL9910/AL9910A/AL9910-5
Document number: DS 35103 Rev. 3 - 2
IN
. So either maximum duty cycle should be kept below 50% or use of constant off-time removes this issue.
L
V
t
ON
OUT
=
0
V
=
3 .
IN
=
f
OSC
∗
∗
1
D
I
V
t
LED
−
ON
IN
D
V
D
IN
=
OSC
V
C1
OUT
V
, the on-time of the MOSFET can be calculated:
OUT
(Continued)
−
C2
V
IN
Fig. 5 Boost LED driver
UNIVERSAL HIGH VOLTAGE HIGH BRIGHTNESS LED
V
LD
PWM_D
DD
R
OSC
www.diodes.com
AL9910/A
R
OSC
12 of 15
AL9910/AL9910A/AL9910-5
GND
V
IN
GATE
CS
R
Q1
SENSE
L1
D1
C3
© Diodes Incorporated
June 2011
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