NCP1611ADR2G ONSEMI [ON Semiconductor], NCP1611ADR2G Datasheet - Page 18

• Manufacturer Part Number: NCP1611ADR2G
• Description: Enhanced, High-Efficiency Power Factor Controller
• Manufacturer: ONSEMI [ON Semiconductor]

boost stage is operating in CrM but as the load is reduced, the
controller enters controlled frequency discontinuous
operation.
of the input current (“current information”) is generated. If
this signal is higher than a 2.5 V internal reference (named
“Dead−Time Ramp Threshold” in Figure 60), there is no
dead−time and the circuit operates in CrM. If the current
information is lower than the 2.5 V threshold, a dead−time
is inserted that lasts for the time necessary for the internal
As illustrated in Figure 59, under high load conditions, the
Figure 60 details the operation. A voltage representative
− Maximum Current Limit: the circuit senses the
− Under−V oltage Protection: this circuit turns off when
− Brown−Out Detection: the circuit detects low ac line
− Thermal Shutdown: an internal thermal circuitry
MOSFET current and turns off the power switch if
the set current limit is exceeded. In addition, the
circuit enters a low duty−cycle operation mode when
the current reaches 150% of the current limit as a
result of the inductor saturation or a short of the
bypass diode.
it detects that the output voltage is below 12% of the
voltage reference (typically). This feature protects
the PFC stage if the ac line is too low or if there is a
failure in the feedback network (e.g., bad
connection).
conditions and stops operation thus protecting the
PFC stage from excessive stress.
disables the gate drive when the junction
High Current
High Current
No delay è CrM
No delay è CrM
Low Current
Low Current
The next cycle is
The next cycle is
delayed
delayed
Lower Current
Lower Current
Longer dead− time
Longer dead− time
Figure 59. CCFF Operation
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NCP1611 Operation Modes
a Current Controlled Frequency Fold−back (CCFF) where:
ramp to reach 2.5 V from the current information floor.
Hence, the lower the current information is, the longer the
dead−time. When the current information is 0.75 V, the
dead−time is 50
stretched until its drain−source voltage is at its valley. As
illustrated in Figure 60, the ramp is synchronized to the
drain−source ringing. If the ramp exceeds the 2.5 V
threshold while the drain−source voltage is below V
ramp is extended until it oscillates above V
will turn on at the next valley.
As mentioned, the NCP1611 PFC controller implements
To further reduce the losses, the MOSFET turns on is
Output Stage Totem Pole: the NCP1611 incorporates a
−0.5 A / +0.8 A gate driver to efficiently drive most
TO220 or TO247 power MOSFETs.
− The circuit operates in classical Critical conduction
− When the current is below this preset level, the
temperature exceeds 150°C (typically). The circuit
resumes operation once the temperature drops below
approximately 100°C (50°C hysteresis).
Mode (CrM) when the inductor current exceeds a
programmable value.
NCP1611 linearly reduces the operating frequency
down to about 20 kHz when the current is zero.
Timer delay
Timer delay
Timer delay
Timer delay
m
s.
in
so that the drive
in
, the