NCL30002 查看數據表（PDF） - ON Semiconductor

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NCL30002

Power Factor Corrected Buck LED Driver

ON Semiconductor 

NCL30002

AC1 F1

EMI Filter/ Rectifier / Surge Suppression Start−up Resistors HVDC Filter Caps

Lemi1

L4

Output Filter Cap

LED +

AC2

RV1

AC1 +

C6

MOV

AC2 −

D4

Lemi2

Rstart

Rtop

Rin

Rfb

Cfilter

Rbottom Ccomp

1

2

3

4

U1

MFP Vcc

Comp DRV

CT GND

CS ZCD

8

7

6

5

NCL30002

Ct

Feed Forward Compensation

On Time Capacitor

C4

Dbuck

Dvcc

R15

Cvcc

Vcc Bootstrap

Qbuck

Rzcd Rgdrv

ZCD

Current Sense

R8

R2 (Optional)

Rsense

Dovp

Cout

OVP Zener

LED −

Lout

Figure 2. Simplified PFC Buck Application

Overview

Figure 2 illustrates the basic NCL30002 architecture for

a non-isolated low power high power factor LED driver. One

of the notable features of this architecture is the open loop

control. Notice that there is no direct measurement of the

LED current. Tight peak current control coupled with line

feed-forward compensation to vary the on-time allows for

accurate LED drive current. Fortunately in the vast majority

of LED bulb and luminaire applications, the LED forward

voltage range is well bounded and the line voltage may be

limited to one operating range. This is a huge advantage

which makes the simplicity of open loop control possible.

Buck switching on the low side eliminates a floating gate

drive but references the LED to the HV rail. Buck converters

only produce output when the input voltage exceeds the load

voltage. Consequently, the input current goes to zero near

the zero crossing of the line. The exact phase angle of this

event depends on the LED string voltage and the line

voltage. Unlike the boost PFC, the buck PFC has increased

distortion near the zero crossing. However even with cross

over distortion, high power factor and acceptable harmonics

can be achieved.

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