NCP1603 ON Semiconductor, NCP1603 Datasheet - Page 24

• Manufacturer Part Number: NCP1603
• Description: PFC/PWM Combo Controller
• Manufacturer: ON Semiconductor

Feedback in PFC Section
V
FB1 pin (Pin 9) of NCP1603. The FB1 pin voltage V
typically smaller than 5.0 V referring to Figure 31. It is
much lower than V
V
where R
(Pin 9) and the output voltage referring to Figure 45.
voltage V
regulation,
overvoltage protection (OVP).
Bulk Voltage Regulation in PFC Section
voltage V
with a reference current (I
Figure 63. When I
is the output of the regulation block is as high as
V
value on V
V
becomes 0 V that gives no MOSFET on time and V
decreases. As a result, the bulk voltage V
around the range between 96% and 100% of the nominal
value of R
level, the V
in high V
output voltage is higher based on the regulation block
characteristic in Figure 63. In other words, the V
the low V
condition. In order to not over−design the circuit in the
application, the V
very closed to V
almost 96% of the nominal value of R
condition.
bulk
FB1
control(max)
bulk
The output voltage of the PFC circuit (i.e., bulk voltage
Then, the feedback current I
PFC−stage feedback current I
Based on Equations 13 and 14 for a particular power
) is sensed as a feedback current I
is generally neglected.
increases. When I
FB1
ac
bulk
bulk
ac
FB1
condition V
ton
control
is the feedback resistor connected the FB1 pin
I FB1 +
(1.05 V typical) that it gives the maximum
condition is much higher than the high V
or the PFC−stage output voltage, is regulated
1 V
and will be used in the PFC section voltage
undervoltage
× I
Figure 63. Regulation Block
and the maximum MOSFET on time and
control(max)
ref
is inversely proportional to V
control
FB1
.
bulk
V
V bulk * V FB1
reg
is lower than 96% of I
96%
control
that is typically 400 V. Therefore,
in the low V
FB1
R FB1
ref
. It makes the output voltage be
I
ref
= 203 mA typical) as shown in
is lower. It means that I
is higher than I
protection
FB1
I
ref
FB1
[
ac
, that presents bulk
FB1
represents the bulk
FB1
I
condition is usually
V bulk
R FB1
FB1
× I
bulk
flowing into the
ref
(UVP),
ref
, the V
ref
is regulated
ac
in high V
, the V
2
. Hence,
control
(eq. 19)
reg
http://onsemi.com
FB1
FB1
and
that
bulk
reg
NCP1603
or
in
ac
ac
is
24
precision resistors in order to set the nominal V
precisely and for safety purpose.
voltage V
(300 kW typical) for the low−pass filter in Figure 62. The
V
collected in the V
that is then compared to a ramp signal to generate the
MOSFET on time t
Current Sense in PFC Section
current sense scheme in Figure 64. This scheme has the
advantages of: (1) the inrush current limitation by the
resistor. R
current detection implemented in the same pin.
negative voltage. This voltage is measured by a current I
flowing out of the CS1 pin (Pin 11). CS1 pin has an offset
voltage V
zero inductor current I
current I
typical variation of offset voltage V
I
is derived.
Zero Current Detection (ZCD) in PFC Section
pin (Pin 11) sense current I
typical). The offset voltage of the CS1 pin in this condition
is V
at the ZCD condition is derived in Equation 21.
S
control
The feedback resistor R
The regulation block output V
The PFC section senses the inductor current I
Inductor current I
The device recognizes zero inductor current when CS1
is shown in Figure 35. Based on Figure 64, Equation 20
S(ZCD)
R
Figure 64. Current Sense in PFC Section
R
CS1
L(OCP)
and the time information of zero current are
S1
S
CS1
control
. This offset voltage is studied in the setting of
I L(ZCD) +
(7.5 mV typical). The inductor current I
. and (2) the overcurrent protection and zero
V S * R S1 I S + −R CS1 I L
I
I
(i.e., overcurrent protection threshold). A
S
L
control
through an internal resistor R
1
L
for power factor correction.
R S1 I S(ZCD) * V S(ZCD)
passes through R
CS1
L(ZCD)
V
processing circuit to generate V
+
−
S
I
L
FB1
S
is smaller than I
NCP1603
consists of two or three high
and the maximum inductor
R CS1
reg
Gnd1
is connected to control
S
versus sense current
CS1
S(ZCD)
and creates a
L
(eq. 20)
(eq. 21)
(14 mA
by the
L(ZCD)
control
bulk
ton
S