AL9910/AL9910A/AL9910-5

UNIVERSAL HIGH VOLTAGE HIGH BRIGHTNESS LED DRIVER

AL9910/AL9910A/AL9910-5

Document number: DS35103 Rev. 7 - 2

11 of 16

www.diodes.com

February 2012

© Diodes Incorporated

Input Bulk Capacitor

For Offline lamps an input bulk capacitor is required to ensure that the rectified AC voltage is held above twice the LED string

voltage throughout the AC line cycle. The value can be calculated from:

≥

IN

C

MAX

_

DC

L

MIN

_

LINE

CH

IN

V

f

2

V

2

)

D

1

(

P

Δ

×

×

×

−

×

Where

ch

D

L

MAX

_

DC

V

Δ

MIN

_

LINE

V

2

If the capacitor has a 15% voltage ripple then a simplified formula for the minimum value of the bulk input capacitor

approximates to:

2

IN

LEDs

LED

V

0.06

V

I

×

×

Power Factor Correction

If power factor improvement is required then for the input power less than 25W, a simple passive power factor correction

circuit can be added to the AL9910 typical application circuit. Figure 4 shows that passive PFC circuitry (3 current steering

diodes and 2 identical capacitors) does not significantly affect the rest of the circuit. Simple passive PFC improves the line

current harmonic distortion and achieves a power factor greater than 0.85.

Fig. 4 Typical Application Circuit with Passive PFC

Each of these identical capacitors should be rated for half of the input voltage and have twice as much capacitance as the

For further design information please see AN75 from the Diodes website.

R

SENSE

AL9910/A

GATE

CS

LD

PWM_D

GND

R

OSC

V

DD

V

IN

LED +

LED -

V

Q1

L1

D1

R

OSC

C3

C4

BR1

Passive PFC

C1

C2

R

SENSE

AL9910/A

GATE

CS

LD

PWM_D

GND

R

OSC

V

DD

V

IN

LED +

LED -

V

Q1

L1

D1

R

OSC

C3

C4

BR1

Passive PFC

C1

C2