NCP1215 查看數據表（PDF） - ON Semiconductor
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NCP1215 Datasheet PDF : 16 Pages
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NCP1215
The EF16 core for transformer was selected. It has
cross−section area Ae = 20.1 mm2. The N67 magnetic
allows to use maximum operating flux density
Bmax = 0.28 Tesla.
The number of turns of the primary winding is:
np
+
Lp · Ippk
B max · Ae
+
4.14 ·
0.28
10−3 · 0.2047
· 20.1 · 10−6
+
150
turns
(eq. 20)
The AL factor of the transformer’s core can be calculated:
AL
+
Lp
(np)2
+
4.14 · 10−3
(150)2
·
+
184
nH
(eq. 21)
For an adapter output voltage of 6.5 V, the number of turns
of the secondary winding can be calculated accounting
Schottky diode for output rectifier as follows:
ns
+
(Vs
) Vfwd)(1 * d
d max · Vbulk−
max)np
min
(eq. 22)
+
(6.5
)
0.7)(1 * 0.5)150
0.5 · 127
+
8.5
+
9
turns
The number of turns for auxiliary winding can be
calculated similarly:
ns
+
(Vs
) Vfwd)(1 * d
d max · Vbulk−
max)np
min
(eq. 23)
+
(12
)
1)(1
0.5 ·
* 0.5)150
127
+
15.35
+
15
turns
The peak primary current is known from initial
calculations. The current sense method allows choosing the
voltage drop across the current sense resistor. Let’s use a
value of 0.5 V. The value of the current sense resistor can
then be evaluated as follows:
RCS
+
VCS
Ippk
+
0.5
0.2047
+
2.442
W
+
2.7
W
(eq. 24)
The voltage drop across the sense resistor needs to be
recalculated:
VCS + RCS · Ippk + 2.7 · 0.2047 + 0.553 V (eq. 25)
Using the above results the value of the shift resistor is:
Rshift
+
VCS
ICS
+
0.553
50 · 10−6
+
11.06
kW
+
11
kW
(eq.
26)
The value of timing capacitor for the off time control has
to be calculated for minimum bulk capacitor voltage since
at these conditions the converter should be able to deliver
specified maximum output power. The value of the timing
capacitor is then given by the following equation:
CT
+
1
fsw
*
1.2
Lp · Ippk
Vbulk− min
· 106
(eq. 27)
+
75
1
· 103
* 4.14 · 10*3 ·
127
0.12 · 106
0.2047
+
55.5
pF
+
56
pF
The value of the startup resistor for startup time of 200 ms
and Vcc capacitor of 200 nF is following:
Rstartup
+
CVcc
Vbulk− min
Vstartup
tstartup
)
ICC−start
MAX
+
200
·
10−9
127
12
0.2
)
10
·
10−6
+ 5.77 MW + 5.6 MW
(eq. 28)
The result of all the calculations is the application
schematic depicted in Figure 21.
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