NCP1608 Ver la hoja de datos (PDF) - ON Semiconductor

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Fabricante

NCP1608

Critical Conduction Mode PFC Controller Utilizing OTA

ON Semiconductor 

NCP1608

VControl

Ct(offset)

VCt

VCt(off)

DRV

Low VControl Voltage

Noise Induced Voltage Spike

VControl − Ct(offset)

Low VCt(off) Voltage

VZCD

VZCD(ARM)

VZCD(TRIG)

VCL(NEG)

VZCD(ARM)

is Not Exceeded

0V

ton(loop)

DRV Remains Off

ton

tstart

Figure 37. Ct Pin Noise Induced On Time

Reduction and Pulse Skipping

The wide control range of the NCP1608 increases

VControl and VCt(off) in comparison to devices with less

control range. Figure 38 compares VCt(off) of the NCP1608

to a device with a 3 V control range for an application with

the following parameters:

Pout = 250 W

L = 200 mH

h = 92%

VacLL = 85 Vac

VacHL = 265 Vac

Figure 38 shows that VCt(off) of the NCP1608 is 50%

larger than the 3 V control range device. The 50% increase

enables the NCP1608 to prevent inadvertent skipping at

high input voltages and high output power.

0.55

0.50 Vac = 265 Vac

0.45

NCP1608

0.40

0.35

0.30

0.25

0.20

3 V Control

0.15

Range

0.10

0.05

0

25

75

125

175

225 275

Pout, OUTPUT POWER (W)

Figure 38. Comparison of Ct Charging Threshold

vs. Output Power

Startup

Generally, a resistor connected between the rectified ac

line and VCC charges the VCC capacitor to VCC(on). The low

startup current consumption (< 35 mA) enables minimized

standby power dissipation and reduced startup durations.

When VCC exceeds VCC(on), the internal references and

logic of the NCP1608 are enabled. The controller includes

an undervoltage lockout (UVLO) feature that ensures that

the NCP1608 is enabled until VCC decreases to less than

VCC(off). This hysteresis ensures sufficient time for the

auxiliary winding to supply VCC (Figure 39).

VCC

VCC(on)

VCC(off)

Figure 39. Typical VCC Startup Waveform

When the PFC pre-converter is loaded by a switch−mode

power supply (SMPS), it is generally preferable for the

SMPS controller to startup first. The SMPS then supplies

the NCP1608 VCC. Advanced controllers, such as the

NCP1230 or NCP1381, control the enabling of the PFC

stage (see Figure 40) and achieve optimal system

performance. This sequence eliminates the startup resistors

and improves the standby power dissipation of the system.

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