AN1262 APPLICATION NOTE

14/42

Table 11. Wire Table (RS-214). Copper wire. Heavy insulation.

Finally the total winding area must be checked to make sure they fit the bobbin window Aw:

(14)

where Api and Asi are the individual wire cross-section, primary and secondary respectively, including isola-

tion. If the above inequality is not verified there are the following options:

b) choose a smaller wire, recalculate Nwp and Nws and recheck window fitting;

c) use fewer wires in a strand accepting a likely larger temperature rise;

d) use the next size core and restart from step 2.

Finally, the auxiliary winding will be defined. It has not been considered before because it handles a very low

power, thus it will be made with a single thin wire (e.g. AWG32 or AWG33) which gives a negligible contribu-

tion to winding build and losses. Just the turns number needs to be defined:

(15)

where 0.7 V is the typical forward drop on the auxiliary (small signal) diode.

secondary windings has to be calculated first:

;

,

AWG

Diameter

Copper

[cm]

Diameter

Insulated

[cm]

Area

Copper

Area

Insulated

22

0.064

0.071

0.003255

0.004013

23

0.057

0.064

0.002582

0.003221

24

0.051

0.057

0.002047

0.002586

25

0.045

0.051

0.001624

0.002078

26

0.040

0.046

0.001287

0.001671

27

0.036

0.041

0.001021

0.001344

28

0.032

0.037

0.000810

0.001083

29

0.029

0.033

0.000642

0.000872

30

0.025

0.030

0.000509

0.000704

31

0.023

0.027

0.000404

0.000568

32

0.020

0.024

0.000320

0.000459

33

0.018

0.022

0.000254

0.000371

N

aux

Ns

V

CC

0.7

+

V

out

V

F

+

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

⋅

=

Rp

ρ

100

Np L

t

⋅

Nw p Ap

Cu

⋅

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

⋅

=

Rs

ρ

100

Ns L

t

⋅

Nws As

Cu

⋅

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

⋅

=