11/18

AN1606 APPLICATION NOTE

The coil requirements can be met using a gapped core set type E66/33/27, characterized with the following key

parameters:

Ae = 550mm^3;

lcore = 146mm;

m_core = >1600;

Vcore = 80.4*10^3mm^3

The air gap needed to avoid saturation and optimize the coil size is equal to lap = 3mm.

Using the parameters in the formula g).

Vcore>67.5mm^3

This result confirms the core is well above the minimum size.

The used formula for the number of turnes, needed to design the total required inductance L, is:

h)

The resulting N=38, in our solution, has been realized with 19 turns +19 turns.

In order to minimize the high frequency losses, the winding has been made using the "multiple wire" approach.

It is possible to estimate the losses for a low frequency current.

Imposing a maximum power value to be dissipated in the copper (Pcu = 5W)

i)

Using the formula for multiple wires: -

l)

Were:

In practice 20 wires were used, each having a diameter d=0.4 mm.

Output Capacitor filter.

For the bulk capacitor selection, we consider a reasonable 100Hz voltage ripple.

N

L

µ

0

------

l core

,

µ

A

⋅

,

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

1gap

A

π

4

---

1gap

⋅

+





2

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

+

⋅

=

P

wi r e

R

DC

I

RM S m ax

,

2

5W

<

⋅

=

R

DC

P

wire

I

RM S m ax

,

2

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

60m

Ω

=

<

R

DC

ρ

Cu

l

tu rn

N

⋅

π

4

---

d

2

M

⋅⋅

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

60m

Ω

<

⋅

=