NCP1601A Ver la hoja de datos (PDF) - ON Semiconductor
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NCP1601A Datasheet PDF : 18 Pages
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NCP1601A, NCP1601B
Vton + Vcontrol
for CRM (eq.5b)
It is noted that Vton is always greater than or equal to
Vcontrol (i.e., Vton ≥ Vcontrol).
In summary, the input impedance Zin in (eq.6) is obtained
from (eq.1)−(eq.5)
Zin
+
Vin
Iin
+
2 L Ich
Cramp Vcontrol
(eq.6)
Control voltage Vcontrol comes from the PFC output
voltage Vout which is a slowly varying signal. The
bandwidth of Vcontrol can be additionally limited by
inserting an external capacitor Ccontrol to the Vcontrol pin
(Pin 2) in Figure 28. The internal 300 kW resistor and the
capacitor Ccontrol create a low−pass filter which has a
bandwidth fcontrol in (eq.7). It is generally recommended to
limit the bandwidth below 20 Hz to achieve power factor
correction. Typical value of Ccontrol is 0.1 mF.
Ccontrol
u
1
2p300kW
fcontrol
(eq.7)
If the bandwidth of Vcontrol is much less than the 50 or
60 Hz line frequency, the input impedance Zin is slowly
varying or roughly constant. Then, the power factor
correction is achieved in DCM and CRM.
Vreg
96% Iref Iref IFB
Regulation Block
300k
Vcontrol
Processing
Circuit
2
Vcontrol
Ccontrol
Figure 30. Vcontrol Low−Pass Filtering
Maximum Power
Input and output power (Pin and Pout) are derived in
(eq.8) when the circuit efficiency h is obtained or assumed.
The variable Vac stands for the RMS input voltage.
Pin
+
Vac2
Zin
+
Vac2CrampVcontrol
2LIch
(eq.8a)
Pout
+
h
Pin
+
hVac2CrampVcontrol
2LIch
(eq.8b)
From (eq.8), control voltage Vcontrol controls the amount
of output power, input power, or input impedance. The
maximum value of the control voltage Vcontrol is 1.05 V
(i.e., Vcontrol(max) = 1.05 V). A parameter called maximum
power resistor Rpower (10.5 kW typical) is defined in (eq.9)
and restricted to have a maximum ±10% variation
(i.e., 9.5 kW ≤ Rpower ≤ 11.5 kW) for defining the maximum
power in an application.
Rpower
+
Vcontrol(max)
Ich
+
1.05 V
100 mA
+
10.5
kW
(eq.9)
It means that the maximum input and output power
(Pin(max) and Pout(max)) are limited to ±10% variation.
Pin(max)
+
Vac2CrampRpower
2L
(eq.10a)
Pout(max)
+
hVac2CrampRpower
2L
(eq.10b)
The maximum input current Iac(max) to deliver the
maximum input power Pin(max) is also derived in (eq.11).
The suffix ac stands for RMS value.
Iac(max)
+
Pin(max)
Vac
+
VacCrampRpower
2L
(eq.11)
Output Feedback
The output voltage Vout of the PFC circuit is sensed as a
feedback current IFB flowing into the FB pin (Pin 1) of the
device. The FB pin voltage VFB1 is typically less than 5 V
referring to Figure 11. It is much lower than Vout which is
typically 400 V. Therefore, VFB1 is generally neglected.
IFB
+
Vout * VFB1
RFB
[
Vout
RFB
(eq.12)
where RFB is the feedback resistor connected between the
FB pin (Pin 1) and the output voltage referring to Figure 2.
Then, the feedback current IFB represents the output
voltage Vout and will be used in the output voltage
regulation, Undervoltage Protection (UVP), and
Overvoltage Protection (OVP).
Output Voltage Regulation
Feedback current IFB, which presents output voltage
Vout, is regulated with a reference current (Iref = 203 mA
typical) as shown in Figure 31.
Vreg
1.05 V
96% Iref Iref IFB
Figure 31. Regulation Block
When IFB is lower than 96% of Iref, the Vreg which is the
output of the regulation block is as high as Vcontrol(max)
(1.05 V typical) that gives the maximum value on Vton. As
a result, it gives the maximum MOSFET on time and Vout
increases. When IFB is higher than Iref, the Vreg becomes 0
V that gives no MOSFET on time and Vout decreases. As
a result, the output voltage Vout is regulated around the
range between 96% and 100% of the nominal value of RFB
× Iref.
Based on (eq.8) for a particular power level, the Vcontrol
is inversely proportional to Vac2. Hence, in high Vac
condition Vcontrol is lower. It means that IFB or output
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