NCP1612B 데이터 시트보기 (PDF) - ON Semiconductor

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NCP1612B

Enhanced, High‐Efficiency Power Factor Controller

ON Semiconductor 

NCP1612A, NCP1612B, NCP1612A1, NCP1612A2, NCP1612A3, NCP1612B2

− Maximum Current Limit: the circuit senses the

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.

− Under-Voltage Protection: this circuit turns off when

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).

− Fast Over-Voltage Detection (Fast OVP): the FOVP

pin provides a redundant protection in the case of an

excessive output voltage level. Note that with the

NCP1612A2 and NCP1612B2 versions, the fast

OVP latches off the circuit.

− Bulk Under-Voltage Detection (BUV): The BUV

function is implemented to prevent the downstream

converter from operating when the buck voltage is

too low. Practically, the BUV comparator monitors

the FOVP pin (NCP1612A, NCP1612A1,

NCP1612A3 and NCP1612B) or the FB pin

(NCP1612A2, NCP1612B2) to disable the driver,

gradually discharge the control pin and ground the

High Current

No Delay → CrM

pfcOK pin when the sensed voltage drops below the

BUV threshold (40% of the 2.5 V reference voltage

with the A1/A3 version, 76% with the other

versions). The BUV function has no action

whenever the pfcOK pin is in low state.

− Brown-Out Detection: the circuit detects low ac line

conditions and stops operation thus protecting the

PFC stage from excessive stress.

− Thermal Shutdown: an internal thermal circuitry

disables the gate drive when the junction

temperature exceeds 150°C (typically). The circuit

resumes operation once the temperature drops below

approximately 100°C (50°C hysteresis).

• Output Stage Totem Pole: the NCP1612 incorporates

a −0.5 A/+0.8 A gate driver to efficiently drive most

TO220 or TO247 power MOSFETs.

NCP1612 Operation Modes

As mentioned, the NCP1612 PFC controller implements

a Current Controlled Frequency Fold-back (CCFF) where:

• The circuit operates in classical Critical conduction

Mode (CrM) when the inductor current exceeds

a programmable value.

• When the current is below this preset level,

the NCP1612 linearly reduces the operating frequency

down to about 20 kHz when the current is zero.

Low Current

The Next Cycle is

Delayed

Lower Current

Longer Dead-time

Timer Delay

Timer Delay

Figure 61. CCFF Operation

As illustrated in Figure 61, under high load conditions, the

boost stage is operating in CrM but as the load is reduced, the

controller enters controlled frequency discontinuous

operation.

Figure 62 details the operation. A voltage representative 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 62), 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 ramp

to reach 2.5 V from the current information floor. Hence, the

lower the current information is, the longer the dead-time. For

all versions except NCP1612A3, the maximum dead-time is

approximately 48.5 ms when the current information is

0.65 V typically. The NCP1612A3 limits the maximum

dead-time to 41.5 ms typically when the current information

is 0.90 V typically. In both cases, if the current information

further decreases, the circuit enters skip mode (see next

section).

To further reduce the losses, the MOSFET turns on is

stretched until its drain-source voltage is at its valley. As

illustrated in Figure 62, 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 Vin, the ramp is

extended until it oscillates above Vin so that the drive will turn

on at the next valley.

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