ncp1608d ON Semiconductor, ncp1608d Datasheet - Page 13

• Manufacturer Part Number: ncp1608d
• Description: Critical Conduction Mode Pfc Controller Utilizing Ota
• Manufacturer: ON Semiconductor

output voltage (V
output voltage is less than the target output voltage, then
V
voltage (V
which increases the power delivered to the output. The
increase in delivered power causes V
target output voltage is achieved. Alternatively, if V
greater than the target output voltage, then V
decreases to cause the on time to decrease until V
decreases to the target output voltage. This cause and effect
regulates V
to FB through R
presence of R
in the divider network calculation.
the tradeoff of noise immunity and power dissipation. R
is calculated using the optimized bias current and output
voltage using Equation 3:
a ripple at a frequency of either 100 Hz (for a 50 Hz line
frequency in Europe) or 120 Hz (for a 60 Hz line frequency
in the USA). The V
loop to ensure V
for the proper shaping of the line current. To ensure V
is constant during the ac line cycle, the loop bandwidth is
typically set below 20 Hz. A type 1 compensation network
consists of a capacitor connected between the Control and
ground pins (see Figure 1). In this configuration, the
capacitor necessary to attenuate the V
calculated using Equation 5:
FB
A resistor divider (R
The output voltage is set using Equation 2:
The divider network bias current is selected to optimize
Due to the charging/discharging of C
is less than V
V
out
Control
out
+ V
FB
so that the scaled down V
(4.6 MW typical value) for FPP is included
Control
). This increases the on time of the driver,
C
REF
out
out1
COMP
out
REF
) and is connected to the FB pin. If the
@ R
ripple is attenuated by the regulation
out1
and R
is constant during the ac line cycle
and the EA increases the control
+
out1
and R
2 @ p @ f
Figure 30. Output Voltage Ripple for a Constant Output Power
out2
@
R
out2
R
P
gm
out2
out2
in
V
is equal to V
CROSS
out
) scales down the boost
out
) R
@ R
to increase until the
P
bulk
out
FB
out
Vac
FB
, V
that is applied
) 1
out
Iac
out
ripple is
REF
contains
http://onsemi.com
(eq. 2)
(eq. 5)
Control
Control
. The
out
out1
out
is
13
Where I
R
R
sinusoidal line voltage. The converter provides the load
with a power that matches the average demand only. The
output capacitor (C
between the delivered power and the power consumed by
the load. When the power delivered to the load is less than
the power consumed by the load, C
the delivered power is greater than the power consumed by
the load, C
situation is depicted in Figure 30.
Where f
amplifier transconductance. The crossover frequency is set
below 20 Hz.
On Time Sequence
variable off times for a given rms input voltage and output
load. The NCP1608 controls the on time with the capacitor
connected to the Ct pin. A current source charges the Ct
capacitor to a voltage derived from the Control pin voltage
(V
V
When V
out2
out2
Ct(off)
The PFC stage consumes a sinusoidal current from a
The switching pattern consists of constant on times and
Ct(off)
is dependent on V
is calculated using Equation 4:
+ V
). V
bias(out)
CROSS
Ct(off)
R
Control
bulk
Ct(off)
out2
is reached, the drive turns off (Figure 31).
is the crossover frequency and gm is error
is the output divider network bias current.
charges to store the excess energy. The
+
− Ct
is calculated using Equation 6:
R
bulk
R
FB
(offset)
out1
out
) compensates for the difference
@
, R
+
V
R
+
V
REF
out1
I
out1
out
bias(out)
2 @ P
V
out
* 1 * R
, and R
@ R
h @ Vac
out
bulk
FB
@ L @ I
FB
discharges. When
2
@ Ct
.
out1
charge
(eq. 3)
(eq. 4)
(eq. 6)