NCP1607BDR2G【PDF 14/23 页】IC PFC CONTROLLER CRM 8SOIC

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Sheet目录45

10页 11页 12页 13页 [14页]15页 16页 17页 18页

NCP1607

http://onsemi.com

To prevent negative voltages on the ZCD pin, the pin is

internally clamped to V

CL(NEG)

(600 mV typical) when the

ZCD winding is negative. Similarly, the ZCD pin is

clamped to V

CL(POS)

(5.7 V typical), when the voltage rises

too high. Because of these clamps, a resistor (R

ZCD

Figure 29) is necessary to limit the current from the ZCD

winding to the ZCD pin.

At startup, there is no energy in the ZCD winding and

therefore no voltage signal to activate the ZCD

comparators. This means that the driver could never turn

on. Therefore, to enable the PFC stage to startup under

these conditions, an internal watchdog timer is integrated

into the controller. This timer turns the drive on if the driver

has been off for more than 180 ms (typical). This feature is

deactivated during a fault mode (OVP, UVP, or Shutdown),

and reactivated when the fault is removed.

STARTUP

Generally, a resistor connected between the ac input and

(pin 8) charges the V

capacitor to the V

CC(on)

level

(12 V typical). Because of the very low consumption of the

NCP1607 during this stage (< 40 mA), most of the current

goes directly to charging up the V

capacitor. This

provides faster startup times and reduced standby power

dissipation. When the V

voltage exceeds the V

CC(on)

level, the internal references and logic of the NCP1607 turn

on. The controller has an undervoltage lockout (UVLO)

feature which keeps the part active until V

drops below

CC(off)

(9.5 V typical). This hysteresis allows ample time

for the auxiliary winding to take over and supply the

necessary power to V

(Figure 30).

Figure 30. Typical V

Startup Waveform

CC(on)

CC(off)

When the PFC preconverter is loaded by a switch mode

power supply (SMPS), then it is often preferable to have the

SMPS controller startup first. The SMPS can then supply

the NCP1607 V

directly. Advanced controllers, such as

the NCP1230 or NCP1381, can control when to turn on the

PFC stage (see Figure 31) leading to optimal system

performance. This setup also eliminates the startup

resistors and therefore improves the no load power

dissipation of the system.

Figure 31. NCP1607 Supplied by a Downstream SMPS Controller (NCP1230)

NCP1230

BULK

BOOST

PFC_V

QUICK START and SOFT START

At startup, the error amplifier is enabled and Control is

pulled up to V

EAL

(2.1 V typical). This is the lowest level

of control voltage which produces output drives. This

feature, called quick start, eliminates the delay at startup

associated with charging the compensation network to its

minimum level. This also produces a natural softstart

mode where the controllers power ramps up from zero to

the required power (see Figure 32).

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