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| 型号： | LM3445TRIACEVAL |
| 厂商： | National Semiconductor |
| 文件页数： | 13/40页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL LM3445MM |
| 标准包装： | 1 |
| 系列： | PowerWise® |
| 电流 - 输出 / 通道： | 770mA |
| 输出及类型： | 1，非隔离 |
| 特点： | 可调光 |
| 输入电压： | 8 ~ 12V |
| 已供物品： | 板 |
| 已用 IC / 零件： | LM3445MM |
| 相关产品： | LM3445MMX-ND - IC LED DRIVER TRIAC DIMM 10-MSOP LM3445MMDKR-ND - IC LED DRIVER TRIAC DIMM 10-MSOP LM3445MMCT-ND - IC LED DRIVER TRIAC DIMM 10-MSOP LM3445MMTR-ND - IC LED DRIVER TRIAC DIMM 10-MSOP |
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SNVS570L – JANUARY 2009 – REVISED MAY 2013
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 18 illustrates a two and three stage valley-fill circuit.
V+
D3
V BUCK
V + D3
V BUCK
C7
+
D9
R6
C7
+
D6
D9
R6
D8
R8
C10
D8
R8
C10
D4
+
C9
R7
D4
D5
C8
D7
C9
+
R7
Figure 18. Two and Three Stage Valley Fill Circuit
The valley-fill circuit allows the buck regulator to draw power throughout a larger portion of the AC line. This
allows the capacitance needed at V BUCK to be lower than if there were no valley-fill circuit, and adds passive
power factor correction (PFC) to the application. Besides better power factor correction, a valley-fill circuit allows
the buck converter to operate while separate circuitry translates the dimming information. This allows for dimming
that isn’t subject to 120Hz flicker that can be perceived by the human eye.
VALLEY-FILL OPERATION
When the “input line is high”, power is derived directly through D3. The term “input line is high” can be explained
as follows. The valley-fill circuit charges capacitors C7 and C9 in series (see Figure 19 ) when the input line is
high.
V BUCK
V+
D3
+
C7
+
V BUCK
2
-
D8
+
C10
D4
V BUCK
2
+
C9
-
Figure 19. Two Stage Valley-Fill Circuit When AC Line is High
Copyright ? 2009–2013, Texas Instruments Incorporated
Product Folder Links: LM3445
13
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| LM3445TRIACEVAL/NOPB | 制造商:Texas Instruments 功能描述:TRIAC Dimmable Offline LED Driver Evaluation Board |
| LM3447 | 制造商:TI 制造商全称:Texas Instruments 功能描述:Phase Dimmable, Primary Side Power Regulated PFC Flyback Controller for LED Lighting |
| LM3447-A19-120VEVM | 功能描述:LED 照明开发工具 LM3447 Eval Mod RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
| LM3447-A19-230VEVM | 功能描述:LED 照明开发工具 LM3447 Eval Mod RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
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