NCP1653A データシートの表示（PDF） - ON Semiconductor
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NCP1653A Datasheet PDF : 19 Pages
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NCP1653, NCP1653A
stands for the RMS. Ivac is a constant in the 50 or 60 Hz
bandwidth. Multiplier resistor RM is the external resistor
connected to the multiplier voltage VM pin (Pin 5). It is also
constant. RM 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”.
Ivac
+
Ǹ2 Vac
(Rvac )
*4 V
12 kW)
[
Vac
RȀvac
(eq.9)
Sense current IS is proportional to the inductor current IL
as described in (eq.10). IL consists of the high−frequency
component (which depends on di/dt or inductor L) and
low−frequency component (which is IL−50).
IS
+
RCS
RS
IL
(eq.10)
Control current Icontrol is a roughly constant current that
comes from the PFC output voltage Vout that is a slowly
varying signal. The bandwidth of Icontrol can be
additionally limited by inserting an external capacitor
Ccontrol to the control voltage Vcontrol pin (Pin 2) in
Figure 30. It is recommended to limit fcontrol, that is the
bandwidth of Vcontrol (or Icontrol), below 20 Hz typically to
achieve power factor correction purpose. Typical value of
Ccontrol is between 0.1 mF and 0.33 mF.
Vreg
300 k
96% I ref Iref IFB
Regulation Block
I control
=
Vcontrol
R1
2
Vcontrol
Ccontrol
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 Cfilter. Therefore, the multiplier capacitor CM
is generally with a larger value comparing to the filter
capacitor Cfilter.
Input and output power (Pin and Pout) are derived in
(eq.13) when the circuit efficiency η is obtained or
assumed. The variable Vac stands for the RMS input
voltage.
Pin
+
Vac2
Zin
+
2
RS
RȀvac Icontrol Vref
RM RCS Vout
Vac
T
Icontrol Vac
Vout
(eq.13a)
Pout
+
hPin
+
h
2
RS
RȀvac Icontrol Vref
RM RCS Vout
Vac
T
Icontrol Vac
Vout
(eq.13b)
Follower Boost
The NCP1653 operates in follower boost mode when
Icontrol is constant. If Icontrol is constant based on (eq.13), for
a constant load or power demand the output voltage Vout of
the converter is proportional to the RMS input voltage Vac. It
means the output voltage Vout becomes lower when the RMS
input voltage Vac becomes lower. On the other hand, the
output voltage Vout becomes lower when the load or power
demand becomes higher. It is illustrated in Figure 31.
Vout (Traditional boost)
Figure 30. Vcontrol Low−Pass Filtering
Ccontrol
u
2
p
300
1
kW
fcontrol
(eq.11)
From (eq.7)−(eq.10), the input impedance Zin is
re−formulated in (eq.12).
Zin
+
2
RM RCS Vac Vout IL
RS RȀvac Icontrol Vref IL−50
Zin
+
2
RM RCS
RS RȀvac
Vac Vout
Icontrol Vref
whenIL
+
IL−50
(eq.12)
The multiplier capacitor CM is the one to filter the
high−frequency component of the multiplier voltage VM.
The high−frequency component is basically coming from
the inductor current IL. On the other hand, the filter
capacitor Cfilter similarly removes the high−frequency
component of inductor current IL. If the capacitors CM and
Cfilter match with each other in terms of filtering capability,
IL becomes IL−50. Input impedance Zin is roughly constant
Vout (Follower boost)
Vin
time
Pout
time
Figure 31. Follower Boost Characteristics
Follower Boost Benefits
The follower boost circuit offers an opportunity to reduce
the output voltage Vout whenever the RMS input voltage
Vac is lower or the power demand Pout is higher. Because
of the step−up characteristics of boost converter, the output
voltage Vout will always be higher than the input voltage
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