AN1889 STMicroelectronics, AN1889 Datasheet - Page 9

• Manufacturer Part Number: AN1889
• Description: ESBT STC03DE170 IN 3-PHASE AUXILIARY POWER SUPPLY
• Manufacturer: STMicroelectronics

assume the maximum losses on the copper. Normal practice is to choose a dissipation level comparable
with the one achieved in the core, practically we can chose 1W.
From that, knowing the copper resistivity at 100
L
For practical consideration, to better optimize the transformer window utilization and in the main time in
accordance with the above calculation, it has been chosen:
The choice at secondary side of 2 wires of 0.05 mm in parallel vs. one of 0.074 mm has been made to
minimize the skin effect.
During the transformer construction particular care must be put in minimizing the parasitic impedances,
in particular the leakage inductance and the winding capacitance. Practically the leakage inductance
should not exceed 3% of the primary inductance. The use of interleaved winding is a common method to
reduce leakage inductance. Practically half of the primary turns is firstly wound, then the secondary turns
and finally the last half of the primary that must result series connected with the first half-wind of the
primary. To avoid an excessive increase of the winding capacitance the second half of the primary must
be connected with the switch.
The final transformer has been realized from TDK in accordance with the above specification, its relative
part number is SRW2924ED-E02V015. The table below summarizes the most important parameters of
the above-mentioned transformer:
Table 2: Transformer Parameters
From the Joule's law we can calculate the resistance of both primary and secondary winding.
t
(L
t
= 4.1cm), we can easily calculate the wire sections (in cm
Symbol
R
A
P
A
V
A
l
l
CW
e
g
e
e
L
=
I 2
P
2
PRMS
CU
d
p
= 0.025
Cross sectional winding area
Effective cross section Area
R
Effective magnetic path
Single turn inductance
Effective core volume
P
=
. 3
Air gap lenght
Description
46
[cm]
Ω
o
C (
d
s
=0.05 [cm] (2 in parallel)
ρ
100
R
=2.303 10
S
=
I 2
P
2
SRMS
2
Values
115.45
CU
85.78
58.65
5030
)
130
0.8
-6
Ω cm), and the average wind length
R
S
AN1889 - APPLICATION NOTE
=
. 0
Dimension
0174
nH/n
mm
mm
mm
mm
mm
2
3
2
Ω
2
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