NCP1608BOOSTGEVB
http://onsemi.com
2
Figure 2. Schematic and Waveforms of an Ideal CrM Boost Converter
Diode Bridge
AC Line
+
−
L
Diode Bridge
AC Line
+
−
L
+
The power switch is ON
The power switch is OFF
Critical Conduction Mode:
Next current cycle starts
when the core is reset.
Inductor
Current
+
With the power switch voltage being about zero, the
input voltage is applied across the inductor. The induct-
or current linearly increases with a (V
in
/L) slope.
The inductor current flows through the diode. The inductor
voltage is (V
out
−
V
in
) and the inductor current linearly decays
with a (V
out
−
V
in
)/L slope.
V
out
(V
out
−
V
in
)/L
I
L(peak)
I
L
V
in
V
drain
V
drain
V
in
/L
V
out
V
in
If next cycle does not start
then V
drain
rings towards V
in
+
I
L
V
in
V
drain
Features of the NCP1608
The NCP1608 is an excellent controller for robust
medium power CrM boost PFC applications due to its
integrated safety features, low impedance driver, high
precision error amplifier, and low standby current
consumption.
For detailed information on the operation of the
NCP1608, please refer to NCP1608/D at
www.onsemi.com
.
A CrM boost pre-converter featuring the NCP1608 is
shown in Figure 3.
Figure 3. CrM Boost PFC Stage Featuring the NCP1608
+
AC Line
EMI
Filter
1
4
3
2
8
5
6
7
+
C
bulk
LOAD
(Ballast,
SMPS, etc.)
NCP1608
V
out
R
sense
C
in
R
ZCD
R
out1
R
out2
C
COMP
V
CC
C
t
D
L
FB
Control
Ct
CS
GND
ZCD
DRV
V
CC
V
in
N
B
:N
ZCD
M
The FB pin senses the boost output voltage through the
resistor divider formed by R
out1
and R
out2
. The FB pin
includes overvoltage protection (OVP), undervoltage
protection (UVP), and floating pin protection (FPP). This
pin is the input to the error amplifier. The output of the error
amplifier is the Control pin.
A combination of resistors and capacitors connected
between the Control and ground pins forms a compensation
network that limits the bandwidth of the converter. For high
PF, the bandwidth is set to less than 20 Hz. A capacitor
connected to the Ct pin sets the maximum on time. The CS
pin provides cycle
−
by
−
cycle overcurrent protection. The