NCP1606BDR2G【PDF 17/22 页】IC POWER FACTOR CONTROLLER 8SOIC

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Sheet目录45

13页 14页 15页 16页 [17页]18页 19页 20页 21页

NCP1606

http://onsemi.com

For the above example, this leads to:

OUT2

2.5 V

400 V * 2.5 V

@ 1.9 MW + 12.0 kW.

STATIC OVERVOLTAGE PROTECTION

If the OVP condition lasts for a long time, it may happen

that the error amplifier output reaches its minimum level

(i.e. Control = V

EAL

). It would then not be able to sink any

current and maintain the OVP fault. Therefore, to avoid any

discontinuity in the OVP disabling effect, the circuit

incorporates a comparator which detects when the lower

level of the error amplifier is reached. This event, called

static OVP, disables the output drives. Once the OVP

event is over, and the output voltage has dropped to normal,

then Control rises above the lower limit and the driver is

reenabled (Figure 35).

Figure 35. OVP Timing Diagram

Vout

Vcontrol

Icontrol

Dynamic OVP

Static OVP

IovpH

IovpL

Vout(nom)

Drive

EAH

EAL

NCP1606 Undervoltage Protection (UVP)

When the PFC stage is plugged in, the output voltage is

forced to roughly equate the peak line voltage. The

NCP1606 detects an undervoltage fault when this output

voltage is unusually low, such that the feedback voltage is

below V

UVP

(300 mV typ). In an UVP fault, the drive

output and error amplifier (EA) are disabled. The latter is

done so that the EA does not source a current which would

increase the FB voltage and prevent the UVP event from

being accurately detected. The UVP feature helps to

protect the application if something is wrong with the

power path to the bulk capacitor (i.e. the capacitor cannot

charge up) or if the controller cannot sense the bulk voltage

(i.e. the feedback loop is open).

Furthermore, the NCP1606 incorporates a novel startup

sequence which ensures that undervoltage conditions are

always detected at startup. It accomplishes this by waiting

approximately 180 ms after V

reaches V

CC(on)

before

enabling the error amplifier (Figure 36). During this wait

time, it looks to see if the feedback (FB) voltage is greater

than the UVP threshold. If not, then the controller enters a

UVP fault and leaves the error amplifier disabled.

However, if the FB pin voltage increases and exceeds the

UVP level, then the controller will start the application up

normally.

Figure 36. The NCP1606s Startup Sequence with

and without a UVP Fault

Control

2.5 V

UVP

UVP Wait

UVP

EAH

EAL

OUT(nom)

OUT

CC(off)

CC(on)

UVP Fault is Removed

The voltage on the output which exits a UVP fault is

given by:

OUT

(UVP)

OUT1

) R

OUT2

@ 300 mV

(eq. 13)

If R

OUT1

= 1.9 MW and R

OUT2

= 12.0 kW, then the V

OUT

UVP threshold is 48 V. This corresponds to an input voltage

of approximately 34 Vac.

Overcurrent Protection (OCP)

A dedicated pin on the NCP1606 senses the peak current

and limits the driver on time if this current exceeds

CS(limit)

. This level is 1.7 V (typ) on the NCP1606A and

0.5 V (typ) on the NCP1606B. Therefore, the maximum

peak current can be adjusted by changing R

SENSE

according

to:

peak

CS(limit)

SENSE

(eq. 14)

An internal LEB filter (Figure 37) reduces the likelihood

of switching noise falsely triggering the OCP limit. This

filter blanks out the first 250 ns (typical) of the current

sense signal. If additional filtering is necessary, a small RC

filter can be added between R

SENSE

and the CS pin.

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