AL8821

Document number: DS37671 Rev. 1 - 2

9 of 14

www.diodes.com

January 2015

© Diodes Incorporated

AL8821

)

( peak

L

L

I

I

K





3

1

3

1

((

1.5) 0.6 1.4) (2

)

10

1.5

5

32 (

0.444)

-K

=

44 (2

)

10

, 0

1.5

(

0.444)

-K

COMP

IN

COMP

LED

LED

SET

IN

COMP

LED

LED

V

K

V

V

V

V

VI

R

KV

V

V

V

VI

















 

 



















 

 

















（1 ）

（1 ）

4

1

2 (

0.444)

10

=

(2

)

LED

LED

SET

HYS

IN

V

I

K

R

R

VK









 





 

When the value of K,

order to get appropriate efficiency and Electronic Transformer (ET) compatibility, generally K is set between 0.4 and 0.8. Due to the range of

Inductor Selection

Because of the using of the hysteretic control scheme, the switching frequency in a boost configuration can be adjusted in accordance to the value

of the inductor being used. The value of the inductor can be determined on the desired switching frequency by using the following equation:

SW

ave

L

DSON

L

SET

F

LED

L

ave

L

SET

L

F

IN

LED

ave

L

DSON

L

SET

IN

f

I

R

R

R

V

V

I

I

R

R

V

V

V

I

R

R

R

V

L









































]

)

2

2

(

444

.

0

[

]

)

(

444

.

0

[

]

)

(

[

)

(

)

(

1

)

(

1

Where:

L is the coil inductance.

switching loss but need to choose higher inductor values that will result in larger size in order to meet the saturation current. For example the

relationship between switching frequency and inductor value is shown as below Table 1 in the same application system. Considering these factors,

500kHz switching frequency is recommend in typical application.

Operation Frequency of SW at Peak Voltage Of Vac

10µH

840kHz

15µH

800kHz

22µH

680kHz

33µH

465kHZ

Table 1