NCP1381 ONSEMI [ON Semiconductor], NCP1381 Datasheet - Page 13

• Manufacturer Part Number: NCP1381
• Description: Low−Standby High Performance PWM Controller
• Manufacturer: ONSEMI [ON Semiconductor]

Figure 13. The Soft−start Starts During Skip Mode
Figure 14. The 8 ms Timeout Helps to Restart the
and Smooths the Current Signature
Controller
Current Sense and Timeout Restart
8 ms
Demag Restart
8 ms
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NCP1381
13
Overpower Compensation
Conduction Mode (BCM) transfers energy from primary to
secondary according to the following law:
Therefore, we can see that for various switching frequency
values (dependent on the input condition if the output
demand is fixed), the converter will permanently adjust the
peak current I
manipulating the slope definitions S
Figure 8), we can show that the peak current is defined by:
where h is the converter’s efficiency, V
V
graph the peak variation with the input voltage, as depicted
by Figure 16 for a 90 W converter operating on universal
mains and featuring the following parameters:
V
N
R
t
L
Note that these elements were selected to design for a 100 W
value, giving us design margin.
P
Figure 15. The Internal Soft−start is Activated During
out
out
P
sense
P
A FLYBACK converter operating in Borderline
(Propagation Delay) = 100 ns,
:N
= 700 mH, h = 0.85 and V
= 19 V @ 4.7 A,
the output voltage. Feeding a math processor lets us
S
= 0.25 W, 200 VDC − 400 VDC Input Voltage,
= 1:0.166,
P in +
I P + 2 @ P out @
P out
P
h +
to keep the output power constant. By
Each Skipped Cycles
1
2
h @ V in @ N @ (V out ) V F )
@ L P @ I P
N @ (V out ) V F ) ) V in
F
= 0.8 V
2
@ F
SW
ON
in
the input voltage,
and S
OFF
(eq. 2)
(eq. 3)
(see