AN2928

Design equations for the modified buck converter

7/21

time:

Equation 2

Equation 3

∆I

∆I

Equation 4

Using Equation 2 and Equation 3, it is possible to create following equations:

Equation 5

Equation 6

Equation 7

The duty cycle for the modified buck topology (also valid for a standard buck topology)

converter is calculated:

Equation 8

∆I

LON

V

L

L

------ t

d

0

t

ON

∫

V

IN

V

LED

–

() t

ON

⋅

L

--------------------------------------------------

==

∆I

LOFF

V

L

L

------ t

d

t

ON

t

ON

t

OFF

+

∫

V

LED

t

OFF

⋅

L

---------------------------------

–

==

∆l

LON

∆I

LOFF

=

V

IN

V

LED

–

() t

ON

⋅

L

--------------------------------------------------

V

LED

t

OFF

–

()

L

------------------------------------

=

V

IN

t

t

ON

V

LED

t

OFF

⋅

=

⋅

–

⋅

V

IN

t

ON

V

LED

t

OFF

t

ON

+

() V

LED

T

⋅

=

⋅

=

⋅

D

t

ON

T

---------

V

LED

V

IN

--------------

=

=