LM3444_15 Datasheet, PDF (9/27 Pages) Texas Instruments – AC-DC Offline LED Driver

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Feature Description (continued)
LM3444
SNVS682D – NOVEMBER 2010 – REVISED DECEMBER 2015
V+
D3
V_BUCK
C7 ⁺
D9
BR1
C10
R2
D4
D8 _{C9 +}
V_LED
C12
- R4
VAC
Q1
D1
D2
C5
V_LED-
D10
Q3
L2
LM3444
1 NC _U1 NC 10
2 NC
VCC 9
I_COLL
3 NC
GATE ⁸
4 COFF
ISNS ⁷
5 FILTER
GND 6
C4
Q2
R3
C11
Figure 8. LM3444 Schematic
7.3.2 Valley-Fill Circuit
V_BUCK supplies the power which drives the LED string. Diode D3 allows V_BUCK to remain high while V+ cycles on
and off. V_BUCK 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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