ON Semiconductor NCP1608BOOSTGEVB, Руководство пользователя

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NCP1608BOOSTGEVB
http://onsemi.com
8
Figure 8. Using the SMPS Controller to Supply Power to the NCP1608
1
7
6
5
2
3
4
NCP1608
+
+
+
+
1
7
6
5
2
3
4
NCP1230
PFC(V
CC
)
8 8
+
D
C
bulk
V
CC
+
−
DESIGN STEP 8: Limit the Inrush Current
The sudden application of the ac line voltage to the PFC
pre − converter causes an inrush current and a resonant
voltage overshoot that is several times the normal value.
Resizing the power components to handle inrush current and
a resonant voltage overshoot is cost prohibitive.
1. External Inrush Current Limiting Resistor
A NTC (negative temperature coefficient) thermistor
connected in series with the diode limits the inrush current
(Figure 9). The resistance of the NTC decreases from a few
ohms to a few milliohms as the NTC is heated by the I
2
R
power dissipation. However, an NTC resistor may not be
sufficient to protect the inductor and C
bulk
from inrush
current during a brief interruption of the ac line voltage, such
as during ac line dropout and recovery.
2. Startup Bypass Rectifier
A rectifier is connected from V
in
to V
out
(Figure 10). This
bypasses the inductor and diverts the startup current directly
to C
bulk
. C
bulk
is charged to the peak ac line voltage without
resonant overshoot and without excessive inductor current.
After startup, D
bypass
is reverse biased and does not interfere
with the boost converter.
Figure 9. Use a NTC to Limit the Inrush Current
Through the Inductor
NCP1608
+
Vac
NTC
V
in
V
out
Figure 10. Use a Second Diode to Route the
Inrush Current Away from the Inductor
NCP1608
+
Vac
V
in
V
out
D
bypass
DESIGN STEP 9: Develop the Compensation Network
The pre − converter is compensated to ensure stability over
the input voltage and output power range. To compensate the
loop, a compensation network is connected between the
Control and ground pins. To ensure high PF, the bandwidth
of the loop is set below 20 Hz. A type 2 compensation
network is selected for this design to increase the phase
margin. The type 2 compensation network is shown in
Figure 11.
Figure 11. Type 2 Compensation Network
FB
Control
+
−
E/A
+
gm
C
COMP
R
COMP1
C
COMP1
R
out2
R
out1
V
Control
V
out
R
FB
V
REF
Compensation
Network