FSEZ13X7 データシートの表示（PDF） - Fairchild Semiconductor
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FSEZ13X7
Fairchild Semiconductor
FSEZ13X7 Datasheet PDF : 16 Pages
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AN-8033
The maximum peak drain current can be obtained at the
nominal output condition as:
I PK
DS
=
2PIN .T
Lm ⋅ fS
(28)
The MOSFET conduction time at the nominal output
condition is obtained as:
TON
=
I PK
DS
Lm
V min
DL
(29)
The minimum number of turns for the transformer primary
side to avoid the core saturation is given by:
N min
P
=
Lm I DS PK
Bsat Ae
(30)
where Ae is the cross-sectional area of the core in m2 and
Bsat is the saturation flux density in Tesla. Figure 12 shows
the typical characteristics of ferrite core from TDK (PC40).
Since the saturation flux density (Bsat) decreases as the
temperature rises, the high-temperature characteristics
should be considered when it comes to charger in enclosed
case. If there is no reference data, use Bsat =0.25~0.3 T.
Table 2 shows the commonly used cores for battery
chargers with output power under 10W. The cores
recommended in Table 2 are typical for the universal input
range and 50kHz switching frequency.
Once the turns ratio is obtained, determine the proper
integer
for
Ns
so
that
the
resulting
Np
is
larger
than
N min
p
obtained from Equation (30).
Then, the non-conduction time at minimum output voltage
is given as:
TOFF @C
=
1
fSR
− TON @C
(1 +
NS
NP
⋅
V min
DL @ C
V min
O
+ VF
)
(33)
The non-conduction time should be larger than 3µs (10% of
switching period), considering the tolerance of switching
frequency.
Table 2.Typical Cores for Battery Charger Application
(for Universal Input Range, DCM Operation, and
fs=50kHz)
Core
EE13-Z
EI16-Z
EE16-Z
EI19-Z
Cross-sectional Area
17.1mm2
19.8mm2
19.0mm2
24.0mm2
Rated Input Power
4~7W
4~7W
7~14W
7~14W
(Design Example) Setting the non-conduction time at
70% of nominal output voltage as 4µs, the MOSFET
conduction time is obtained as:
TON @ B
=
(1 +
1/
NS
fS
⋅
− TOFF
V min
DL@ B
= 5.4μs
)
NP 0.7 ⋅VO + VF
The transformer primary-side inductance is calculated
as:
Lm
=
(VDL@ Bmin ⋅TON @ B )2
2PIN .T @ B
⋅
fS
=
2.24mH
Then, the peak drain current at maximum output power
condition is given as:
IDS PK =
2PIN.T = 292mA
Lm ⋅ fS
Figure 12. Typical B-H Curves of Ferrite Core
(TDK/PC40)
DCM operation at minimum output voltage should be also
checked. The MOSFET conduction time at minimum
output voltage is given as:
TON @C
=1
V min
DL@ C
2PIN.T @C Lm
fSR
(31)
where fSR is the reduced switching frequency to prevent
CCM operation.
The MOSFET conduction time at the nominal output
condition is obtained as:
TON
=
I PK
DS
Lm
V min
DL
= 0.292 2.24 ×10−3
93
= 7.03μs
EE16 core is selected for the transformer and the
minimum number of turns for the transformer primary
side to avoid the core saturation is given by:
N min
P
=
Lm Ids PK
Bsat Ae
=
2.24 ×10−3 ⋅ 0.292
0.3⋅19 ×10−6
= 114
Then, determine the proper integer for Ns so that the
resulting
Np
is
larger
than
N min
p
NP = 13× NS
= 13× 9 = 117 > NPmin
© 2009 Fairchild Semiconductor Corporation
Rev. 1.0.1 • 5/6/10
8
www.fairchildsemi.com
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