Description

AN4339

12/27

DocID025039 Rev 1

1.3.6

Transformer design

Primary inductance value is calculated by Equation 19:

Equation 19

Lp = 1.25 mH

Select

Lp = 1 mH

Primary to secondary turn ratio:

Equation 20

n = 6.911

Primary number of turns:

Equation 21

Considering max flux density:

Bmax = 0.3 T

Select core EE25 (After calculating the minimum area product required, not described in this

section).

Cross sectional area:

Equation 22

Primary number of turns:

Equation 23

Np = 91

Select Np = 90 T

Secondary number of turns:

Equation 24

Ns = Np/n

Ns = 13 T

Aux. voltage required:

3



1Kv

+

  f

swmin



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

=

n

+

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

=

3

–





4

–





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

=