ICOLL

V+

VAC

+

+

1

2

3

4

5

6

7

8

9

10

-

VLED

GND

VCC

FILTER

NC

NC

ISNS

GATE

NC

COFF

NC

LM3444

VLED-

D3

C7

C9

C10

D4

D8

D9

R2

D1

Q1

C5

C12

D2

D10

Q2

L2

Q3

R3

R4

C11

C4

U1

VBUCK

BR1

LM3444

www.ti.com

SNVS682D – NOVEMBER 2010 – REVISED DECEMBER 2015

Feature Description (continued)

Figure 8. LM3444 Schematic

7.3.2 Valley-Fill Circuit

VBUCK supplies the power which drives the LED string. Diode D3 allows VBUCK to remain high while V+ cycles on

and off. VBUCK has a relatively small hold capacitor C10 which reduces the voltage ripple when the valley fill

capacitors are being charged. However, the network of diodes and capacitors shown between D3 and C10 make

up a valley-fill circuit. The valley-fill circuit can be configured with two or three stages. The most common

configuration is two stages. Figure 9 illustrates a two- and three-stage valley-fill circuit.

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