NCL30002 Просмотр технического описания (PDF) - ON Semiconductor

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NCL30002

Power Factor Corrected Buck LED Driver

ON Semiconductor 

NCL30002

COMP

Ct

VControl

VDD

Icharge

VEAH

+

PWM

−

+

ton

DRV

VCt

Ct(offset)

VCt(off)

VControl − Ct(offset)

VControl

ton(max)

DRV

MOSFET Conduction

Output Rectifier Conduction

Iprimary

0A

Isecondary

0A

DRV

Figure 25. On Time Control

0V

Off Time Sequence

Vout

The off time is determined by the peak inductor current,

the inductance and the output voltage. In mode 2, the off time

is variable because the peak inductor current is not fixed.

However in mode 3, the off time is constant since the peak

current and the output voltage are both fixed. The auxiliary

winding used to provide bias to the NCL30002 is also used

0V

to detect when the current has dropped to zero. This is

VZCD(WIND)

illustrated in Figure 26.

VZCD(WIND),off

0V

VZCD(WIND),on

VCL(POS)

VZCD(ARM)

VZCD(TRIG)

0V

VCL(NEG)

ton

tdiode

toff

tSW

Figure 26. Ideal CrM Waveforms with ZCD Winding

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