NCP1027P100G(2015) Просмотр технического описания (PDF) - ON Semiconductor
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производитель
NCP1027P100G
(Rev.:2015)
(Rev.:2015)
ON Semiconductor
NCP1027P100G Datasheet PDF : 30 Pages
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NCP1027
• Large K: approaching BCM where the rms losses are
the worse, but smaller inductance, leading to a better
leakage inductance.
From Equation 16, a K factor of 0.8 (40% ripple), gives
an inductance of:
L
+
(120 0.49)2
60k 0.8 18.75
+
3.8
mH
DIL
+
Vind
LFSW
+
120
3.8m
0.49
60k
+
258
mA
peak
*
to
*
peak
The peak current can be evaluated to be:
Ipeak
+
Iavg
d
)
DIL
2
+
Ipeak
+
156m
0.49
)
DIL
2
+
447
mA
In Figure 46, I1 can also be calculated:
I1
+
Ipeak−
DIL
2
+
0.447−0.129
+
318
mA
5. Based on the above numbers, we can now
evaluate the conduction losses:
Ǹ ǒ Ǔ Id, rms + I1 Ǹd
1
)
1
3
DIL
2I1
2 + 0.318
0.7
Ǹ ǒ Ǔ 1
)
1
3
0.258
2 0.318
2 + 228 mA rms
HV
HV
If we take the maximum RDS(on) for a 120°C junction
temperature, i.e. 11 W, then conduction losses worse case
are:
Pcond + I2d, rms Rds(on) + 571 mW
6. Off−time and on−time switching losses can be
estimated based on the following calculations:
Poff
+
IpeakVdstoff
6TSW
+
0.447
6
650
15u
40n + 130 mW
(eq. 18)
Pon
+
IpeakN(Vout )
6TSW
Vf)ton
+
0.447
6
114
15u
40n + 22 mW
(eq. 19)
The theoretical total power is then 0.571 + 0.13 + 0.022
= 723 mW.
7. The ramp compensation will be calculated as
suggested by Equation 13 giving a resistor of
78 kW or 82 kW for the normalized value.
Power Switch Circuit Protection
As in any Flyback design, it is important to limit the drain
excursion to a safe value, e.g. below the power switch
circuit BVdss which is 700 V. Figures 47a, b, c present
possible implementations:
HV
Rclamp
Cclamp
D
Dz
D
1
8
1
8
1
8
2
7
2
7
2
7
3
6
3
6
3
6
CVCC +
4
5
CVCC +
4
5
CVCC +
4
5
C
a.
b.
c.
Figure 47. Different Options to Clamp the Leakage Spike
Figure 47a: The simple capacitor limits the voltage
according to Equation 14. This option is only valid for low
power applications, e.g. below 5.0 W, otherwise chances
exist to destroy the MOSFET. After evaluating the leakage
inductance, you can compute C with Equation 15. Typical
values are between 100 pF and up to 470 pF. Large
capacitors increase capacitive losses…
Figure 47b: The most standard circuitry called the RCD
network. You calculate Rclamp and Cclamp using the
following formulae:
Rclamp
+
2Vclamp(Vclamp−(Vout )
LpeakI2peak FSW
Vf)
N)
(eq. 20)
Cclamp
+
Vclamp
VrippleFSWRclamp
(eq. 21)
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