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NCP1653DR2G

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21
NCP1653, NCP1653A
www.onsemi.com
10
FUNCTIONAL DESCRIPTION
Introduction
The NCP1653 is a Power Factor Correction (PFC) boost
controller designed to operate in fixed−frequency
Continuous Conduction Mode (CCM). It can operate in
either peak current−mode or average current−mode.
Fixed−frequency operation eases the compliance with
EMI standards and the limitation of the possible radiated
noise that may pollute surrounding systems. The CCM
operation reduces the application di/dt and the resulting
interference. The NCP1653 is designed in a compact 8−pin
package which offers the minimum number of external
components. It simplifies the design and reduces the cost.
The output stage of the NCP1653 incorporates ±1.5 A
current capability for direct driving of the MOSFET in
high−power applications.
The NCP1653 is implemented in constant output voltage
or follower boost modes. The follower boost mode permits
one to significantly reduce the size of the PFC circuit
inductor and power MOSFET. With this technique, the
output voltage is not set at a constant level but depends on
the RMS input voltage or load demand. It allows lower
output voltage and hence the inductor and power MOSFET
size or cost are reduced.
Hence, NCP1653 is an ideal candidate in high−power
applications where cost−effectiveness, reliability and high
power factor are the key parameters. The NCP1653
incorporates all the necessary features to build a compact
and rugged PFC stage.
The NCP1653 provides the following protection features:
1. Overvoltage Protection (OVP) is activated and
the Drive Output (Pin 7) goes low when the
output voltage exceeds 107% of the nominal
regulation level which is a user−defined value.
The circuit automatically resumes operation when
the output voltage becomes lower than the 107%.
2. Undervoltage Protection (UVP) is activated and
the device is shut down when the output voltage
goes below 8% of the nominal regulation level.
The circuit automatically starts operation when
the output voltage goes above 12% of the
nominal regulation level. This feature also
provides output open−loop protection, and an
external shutdown feature.
3. Overpower Limitation (OPL) is activated and the
Drive Output (Pin 7) duty ratio is reduced by
pulling down an internal signal when a computed
input power exceeds a permissible level. OPL is
automatically deactivated when this computed input
power becomes lower than the permissible level.
4. Overcurrent Protection (OCP) is activated and
the Drive Output (Pin 7) goes low when the
inductor current exceeds a user−defined value.
The operation resumes when the inductor current
becomes lower than this value.
5. Thermal Shutdown (TSD) is activated and the
Drive Output (Pin 7) is disabled when the
junction temperature exceeds 150_C. The
operation resumes when the junction temperature
falls down by typical 30_C.
CCM PFC Boost
A CCM PFC boost converter is shown in Figure 25. The
input voltage is a rectified 50 or 60 Hz sinusoidal signal.
The MOSFET is switching at a high frequency (typically
102 kHz in the NCP1653) so that the inductor current I
L
basically consists of high and low−frequency components.
Filter capacitor C
filter
is an essential and very small value
capacitor in order to eliminate the high−frequency
component of the inductor current I
L
. This filter capacitor
cannot be too bulky because it can pollute the power factor
by distorting the rectified sinusoidal input voltage.
Figure 25. CCM PFC Boost Converter
V
in
I
in
I
L
L
V
out
C
bulk
C
filter
PFC Methodology
The NCP1653 uses a proprietary PFC methodology
particularly designed for CCM operation. The PFC
methodology is described in this section.
Figure 26. Inductor Current in CCM
I
in
t
2
t
1
time
T
I
L
As shown in Figure 26, the inductor current I
L
in a
switching period T includes a charging phase for duration
t
1
and a discharging phase for duration t
2
. The voltage
conversion ratio is obtained in (eq.1).
V
out
V
in
+
t
1
) t
2
t
2
+
T
T * t
1
V
in
+
T * t
1
T
V
out
(eq.1)
NCP1653, NCP1653A
www.onsemi.com
11
The input filter capacitor C
filter
and the front−ended EMI
filter absorbs the high−frequency component of inductor
current I
L
. It makes the input current I
in
a low−frequency
signal only of the inductor current.
I
in
+ I
L−50
(eq.2)
The suffix 50 means it is with a 50 or 60 Hz bandwidth
of the original I
L
.
From (eq.1) and (eq.2), the input impedance Z
in
is
formulated.
Z
in
+
V
in
I
in
+
T * t
1
T
V
out
I
L−50
(eq.3)
Power factor is corrected when the input impedance Z
in
in (eq.3) is constant or slowly varying in the 50 or 60 Hz
bandwidth.
Figure 27. PFC Duty Modulation and Timing Diagram
R
S
Q
0 1
clock
PFC Modulation
Output
Clock
Latch Set
Latch Reset
Inductor
Current
without
filtering
−
+
+
V
ref
V
ref
V
ramp
V
ramp
V
M
V
M
V
M
I
ch
C
ramp
The PFC duty modulation and timing diagram is shown
in Figure 27. The MOSFET on time t
1
is generated by the
intersection of reference voltage V
ref
and ramp voltage
V
ramp
. A relationship in (eq.4) is obtained.
V
ramp
+ V
M
)
I
ch
t
1
C
ramp
+ V
ref
(eq.4)
The charging current I
ch
is specially designed as in
(eq.5). The multiplier voltage V
M
is therefore expressed in
terms of t
1
in (eq.6).
I
ch
+
C
ramp
V
ref
T
(eq.5)
(eq.6)
V
M
+ V
ref
*
t
1
C
ramp
C
ramp
V
ref
T
+ V
ref
T * t
1
T
From (eq.3) and (eq.6), the input impedance Z
in
is
re−formulated in (eq.7).
(eq.7)
Z
in
+
V
M
V
ref
V
out
I
L−50
Because V
ref
and V
out
are roughly constant versus time,
the multiplier voltage V
M
is designed to be proportional to
the I
L−50
in order to have a constant Z
in
for PFC purpose.
It is illustrated in Figure 28.
Figure 28. Multiplier Voltage Timing Diagram
V
in
time
time
V
M
time
I
in
I
L
It can be seen in the timing diagram in Figure 27 that V
M
originally consists of a switching frequency ripple coming
from the inductor current I
L
. The duty ratio can be
inaccurately generated due to this ripple. This modulation
is the so−called “peak current−mode”. Hence, an external
capacitor C
M
connected to the multiplier voltage V
M
pin
(Pin 5) is essential to bypass the high−frequency
component of V
M
. The modulation becomes the so−called
“average current−mode” with a better accuracy for PFC.
Figure 29. External Connection on the Multiplier
Voltage Pin
5
R
M
I
vac
I
S
2I
control
V
M
=
PFC Duty
Modulation
I
M
V
M
R
M
C
M
The multiplier voltage V
M
is generated according to
(eq.8).
V
M
+
R
M
I
vac
I
S
2I
control
(eq.8)
Input−voltage current I
vac
is proportional to the RMS
input voltage V
ac
as described in (eq.9). The suffix ac
NCP1653, NCP1653A
www.onsemi.com
12
stands for the RMS. I
vac
is a constant in the 50 or 60 Hz
bandwidth. Multiplier resistor R
M
is the external resistor
connected to the multiplier voltage V
M
pin (Pin 5). It is also
constant. R
M
directly limits the maximum input power
capability and hence its value affects the NCP1653 to
operate in either “follower boost mode” or “ constant
output voltage mode”.
I
vac
+
2
Ǹ
V
ac
* 4V
ǒ
R
vac
) 12 kW
Ǔ
[
V
ac
RȀ
vac
(eq.9)
Sense current I
S
is proportional to the inductor current I
L
as described in (eq.10). I
L
consists of the high−frequency
component (which depends on di/dt or inductor L) and
low−frequency component (which is I
L−50
).
I
S
+
R
CS
R
S
I
L
(eq.10)
Control current I
control
is a roughly constant current that
comes from the PFC output voltage V
out
that is a slowly
varying signal. The bandwidth of I
control
can be
additionally limited by inserting an external capacitor
C
control
to the control voltage V
control
pin (Pin 2) in
Figure 30. It is recommended to limit f
control
, that is the
bandwidth of V
control
(or I
control
), below 20 Hz typically to
achieve power factor correction purpose. Typical value of
C
control
is between 0.1 mF and 0.33 mF.
Figure 30. V
control
Low−Pass Filtering
FB
ref ref
reg
300 k
C
control
V
I
I
96% I
Regulation Block
2
V
control
I =
control
V
control
R
1
(eq.11)
C
control
u
1
2 p 300 kW f
control
From (eq.7)−(eq.10), the input impedance Z
in
is
re−formulated in (eq.12).
Z
in
+
R
M
R
CS
V
ac
V
out
I
L
2R
S
RȀ
vac
I
control
V
ref
I
L−50
Z
in
+
R
M
R
CS
V
ac
V
out
2R
S
RȀ
vac
I
control
V
ref
whenI
L
+ I
L−50
(eq.12)
The multiplier capacitor C
M
is the one to filter the
high−frequency component of the multiplier voltage V
M
.
The high−frequency component is basically coming from
the inductor current I
L
. On the other hand, the filter
capacitor C
filter
similarly removes the high−frequency
component of inductor current I
L
. If the capacitors C
M
and
C
filter
match with each other in terms of filtering capability,
I
L
becomes I
L−50
. Input impedance Z
in
is roughly constant
over the bandwidth of 50 or 60 Hz and power factor is
corrected.
Practically, the differential−mode inductance in the
front−ended EMI filter improves the filtering performance
of capacitor C
filter
. Therefore, the multiplier capacitor C
M
is generally with a larger value comparing to the filter
capacitor C
filter
.
Input and output power (P
in
and P
out
) are derived in
(eq.13) when the circuit efficiency η is obtained or
assumed. The variable V
ac
stands for the RMS input
voltage.
P
in
+
V
ac
2
Z
in
+
2R
S
RȀ
vac
I
control
V
ref
V
ac
R
M
R
CS
V
out
(eq.13a)
T
I
control
V
ac
V
out
P
out
+ hP
in
+ h
2R
S
RȀ
vac
I
control
V
ref
V
ac
R
M
R
CS
V
out
(eq.13b)
T
I
control
V
ac
V
out
Follower Boost
The NCP1653 operates in follower boost mode when
I
control
is constant. If I
control
is constant based on (eq.13), for
a constant load or power demand the output voltage V
out
of
the converter is proportional to the RMS input voltage V
ac
. It
means the output voltage V
out
becomes lower when the RMS
input voltage V
ac
becomes lower. On the other hand, the
output voltage V
out
becomes lower when the load or power
demand becomes higher. It is illustrated in Figure 31.
Figure 31. Follower Boost Characteristics
V
in
V (Follower boost)
out
time
time
V (Traditional boost)
out
P
out
Follower Boost Benefits
The follower boost circuit offers an opportunity to reduce
the output voltage V
out
whenever the RMS input voltage
V
ac
is lower or the power demand P
out
is higher. Because
of the step−up characteristics of boost converter, the output
voltage V
out
will always be higher than the input voltage
V
in
even though V
out
is reduced in follower boost operation.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21

NCP1653DR2G

Mfr. #:
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Manufacturer:
ON Semiconductor
Description:
Power Factor Correction - PFC Fixed Frequency Current Mode PFC
Lifecycle:
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