Application Note 9 2011-07-06
[11]
The peak current is
AII
rmsrpkr
91.2*2
__
==
. The OCP level is set with about 20% margin:
AII
pkrpkocp
49.3*2.1
__
==
The actual leakage inductance (
leak
L ) measured at primary side with one of the secondary side winding
shorted is around 13uH. Therefore, the inductance for the independent resonant choke is:
If a magnetic core with specs of RM10/PC95 is selected, where
2
min_
90mmA
e
= , and
max
B
is selected
to be 0.08T to reduce core loss, the minimum turns can be given as:
[12]
2.2.7 Transformer design
From Figure 2, the normalized frequency
35.0
min
F
has been located to achieve maximum gain
28.1=
pk
G
. Accordingly the actual minimum frequency
min
f is:
kHzfFf
r
3010*85*35.0*
3
min
===
The voltage across the primary winding can be calculated as
)(
fop
VVnV
. The half switching cycle
period is around:
min
2
1
f
t
= . According to Faraday’s law:
BAN
f
VVn
ep
fo
Δ=
+
min
2
)(
The minimum number of turns at primary side can be found:
BAf
VVn
N
e
fo
p
Δ
+
=
*2
)(
min
min
[13]
Where
2
161mmA
e
= with PQ3230 core. TB 62.0
is selected to avoid magnetic saturation.
Then
minp
N can be calculated as:
33
62.0*10*161*10*30*2
)1.012(*5.16
63
min
=
+
=
−
p
N
The number of turns at primary side is selected as
33
min
p
N . The secondary side turns can be
calculated accordingly:
A
V
P
I
rmsin
in
rmsin
06.2
79.151*96.0
300
*
min__
max__
===
η
4.19
10*90*08.0
49.3*10*40
6
6
minmax
__
min
==
⋅
⋅
=
−
−
LL
pkrchoker
L
AB
IL
N
uHLLL
leakrchoker
40
_
=−=
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