NCP1608BOOSTGEVB
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3
internal comparator compares the voltage developed across
R
sense
(V
CS
) to an internal reference (V
ILIM
). The driver
turns off when V
CS
reaches V
ILIM
. The ZCD pin senses the
demagnetization of the boost inductor to turn on the drive.
The drive on time begins after the ZCD pin voltage (V
ZCD
)
exceeds V
ZCD(ARM)
and then decreases to less than
V
ZCD(TRIG)
. A resistor in series with the ZCD winding
limits the ZCD pin current.
The NCP1608 features a powerful output driver on the
DRV pin. The driver is capable of switching the gates of
large MOSFETs efficiently because of its low source and
sink impedances. The driver includes active and passive
pull
−
down circuits to prevent the output from floating high
when the NCP1608 is disabled.
The V
CC
pin is the supply pin of the controller. When V
CC
is less than the turn on voltage (V
CC(on)
), the current
consumption of the device is less than 35
m
A. This results in
fast startup times and reduced standby power losses.
Design Procedure
The design of a CrM boost PFC converter is discussed in
many ON Semiconductor application notes. Table 1 lists
some examples.
This application note describes the design procedure for
a 400 V, 100 W converter using the features of the NCP1608.
A dedicated NCP1608 design tool that enables users to
determine component values quickly is available at
www.onsemi.com
.
Table 1. Additional Resources for the Design and Understanding of CrM Boost PFC Circuits Available at
www.onsemi.com
.
AND8123
Power Factor Correction Stages Operating in Critical Conduction Mode
AND8016
Design of Power Factor Correction Circuits Using the MC33260
AND8154
NCP1230 90 W, Universal Input Adapter Power Supply with Active PFC
HBD853
Power Factor Correction Handbook
DESIGN STEP 1: Define the Required Parameters
The converter parameters are shown in Table 2.
Table 2. CONVERTER PARAMETERS
Parameter Name
Symbol
Value
Units
Minimum Line Input Voltage
Vac
LL
85
Vac
Maximum Line Input Voltage
Vac
HL
265
Vac
Minimum Line Frequency
f
line(MIN)
47
Hz
Maximum Line Frequency
f
line(MAX)
63
Hz
Output Voltage
V
out
400
V
Full Load Output Current
I
out
250
mA
Full Load Output Power
P
out
100
W
Maximum Output Voltage
V
out(MAX)
440
V
Minimum Switching Frequency
f
SW(MIN)
40
kHz
Minimum Full Load Efficiency
h
92
%
Minimum Full Load Power Factor
PF
0.9
−
DESIGN STEP 2: Calculate the Boost Inductor
The value of the boost inductor (L) is calculated using
Equation 1:
L
v
Vac
2
@
ǒ
V
out
2
Ǹ *
Vac
Ǔ
@
h
2
Ǹ @
V
out
@
P
out
@
f
SW(MIN)
(eq. 1)
To ensure that the switching frequency exceeds the
minimum frequency, L is calculated at both the minimum
and maximum rms input line voltage:
L
LL
v
85
2
@
ǒ
400
2
Ǹ *
85
Ǔ
@
0.92
2
Ǹ @
400
@
100
@
40 k
+
581
m
H
Where L
LL
is the inductor value calculated at Vac
LL
.
L
HL
v
265
2
@
ǒ
400
2
Ǹ *
265
Ǔ
@
0.92
2
Ǹ @
400
@
100
@
40 k
+
509
m
H
Where L
HL
is the inductor value calculated at Vac
HL
.
A value of 400
m
H is selected. The inductance tolerance
is
±
15%. The maximum inductance (L
MAX
) value is
460
m
H. Equation 2 is used to calculate the minimum
frequency at full load.
f
SW
+
Vac
2
@
h
2
@
L
MAX
@
P
out
@
ǒ
1
*
2
Ǹ @
Vac
V
out
Ǔ
(eq. 2)
