AMC7150

Copyright

© 2006 ADDtek Corp.

5

DD034_A

--

JUNE 2006

Inductor

The Inductor L stores energy during switch turn-on period and discharge driving current to LEDs via flywheel

diode while switch turn-off. In order to reduce the current ripple on LEDs, the L value should high enough to keep the

system working at continuous-conduction mode that inductor current won’t fall to zero.

Since in steady-state operation the waveform must repeat from one time period to the next, the integral of the

0

0

0

=

+

=

∫∫

∫

ON

s

ON

s

tT

t

L

L

T

L

dt

v

dt

v

dt

v

Where

OFF

ON

s

t

t

T

+

=

Therefore

LED

SAT

Rsense

CC

F

LED

OFF

ON

V

V

V

V

V

V

t

t

−

−

−

+

=

voltage of the switch which has a typical value of 1V.

turn-on time can also be known by

f

D

T

D

t

s

ON

=

⋅

=

Where

OFF

ON

ON

t

t

t

Dutycycle

D

+

=

)

(

With knowledge of the peak switch current and switch on time, the value of inductance can be calculated.

ON

PK

LED

SAT

Rsense

CC

t

I

V

V

V

V

L

⋅

−

−

−

=