AN458 APPLICATION NOTE

8/19

PD – Losses due to the recirculation diode

PL – Losses due to the coil

Wecan divide these losses in two parts: core losses and copper losses.

The core losses for molypermalloy powder cores are given by the following formula.

where W = watt/lb

f = KHz

N = number of turns

copper losses:

N = number of turns

MLT = lenght/turn for 20% of winding factor

ρ = copper resistivity (1.72 10E-6Wcm)

Refer to table 1 for some

ρ/Aw suggest values.

Table 1.

Typical efficiencies obtained with the test and application circuit of fig. 20 are shown below.

DEVICE DESCRIPTION

Fig.11 shows the pin connection of the Powerdip 12+3+3 plastic package. The internal block diagram of the de-

vice is shown in fig.1. Each block will now be examined in detail.

AWG

Diameter Copper (cm)

OHMS/CM 20C

OHMS/CM 100C

18

.102

.000209

.000280

19

.091

.000264

.000353

20

.081

.000333

.000445

21

.072

.000420

.000561

22

.064

.000530

.000708

PD

VF I

O

V

i

V

O

–

V

i

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

VF I

O

1

V

O

V

i

-------

–





⋅⋅

=

⋅⋅

=

W

0.568 f

1.23

B

2.56

⋅⋅

=

B

KGauss

V

i

V

O

–

() V

O

10

8

⋅⋅

NAe f V

I

⋅⋅

⋅

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

==

P

ρl

2

oMLT N

⋅

–