AN2928

Design equations for the modified buck converter

17/21

Equation 39

N = inductor number of turns (-)

The number of turns for the inductor is:

Equation 40

After the number of turns is calculated, it is also necessary to calculate the wire diameter.

The maximum power loss can be calculated using the maximum inductor temperature and

core thermal resistance with the following equation:

Equation 41

for the E25 core used in the STEVAL-ILL013V1 design is 40 °C/W).

The loss in the core is:

Equation 42

W = core weight (g) (for example, the ETD29 has a weight of 28 g)

Maximum power loss in the wire is simply:

Equation 43

The maximum wire resistance derives from the following equation:

Equation 44

LN

2

A

L

⋅

=

N

L

A

L

------

=

P

MAX LOSS

T

MAX

T

A

–

R

T

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

=

P

CORE

P

V

W10

3

–

⋅⋅

=

P

WI RE

P

MAX LOSS

P

CORE

–

=

R

MAX WIRE

P

WIR E

I

RM S

2

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

=