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| 型号： | LM3445-EDSNEV/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 14/40页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL LED DRIVER LM3445 |
| 标准包装： | 1 |
| 系列： | PowerWise® |
| 电流 - 输出 / 通道： | 205 ~ 340 mA |
| 输出及类型： | 1，非隔离 |
| 特点： | 可调光 |
| 输入电压： | 85 ~ 135 VAC |
| 已供物品： | 板 |
| 已用 IC / 零件： | LM3445 |
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SNVS570L – JANUARY 2009 – REVISED MAY 2013
The peak voltage of a two stage valley-fill capacitor is:
V VF-CAP =
V AC-RMS
2
2
(1)
As the AC line decreases from its peak value every cycle, there will be a point where the voltage magnitude of
the AC line is equal to the voltage that each capacitor is charged. At this point diode D3 becomes reversed
biased, and the capacitors are placed in parallel to each other ( Figure 20 ), and V BUCK equals the capacitor
voltage.
V BUCK
V+
D3
C7
+
+
V BUCK
D9
-
C10
D8
+
D4
V BUCK
+
C9
-
Figure 20. Two Stage Valley-Fill Circuit When AC Line is Low
A three stage valley-fill circuit performs exactly the same as two-stage valley-fill circuit except now three
capacitors are now charged in series, and when the line voltage decreases to:
V VF-CAP =
V AC-RMS
3
2
(2)
Diode D3 is reversed biased and three capacitors are in parallel to each other.
The valley-fill circuit can be optimized for power factor, voltage hold up and overall application size and cost. The
LM3445 will operate with a single stage or a three stage valley-fill circuit as well. Resistor R8 functions as a
current limiting resistor during start-up, and during the transition from series to parallel connection. Resistors R6
and R7 are 1 M ? bleeder resistors, and may or may not be necessary for each application.
BUCK CONVERTER
The LM3445 is a buck controller that uses a proprietary constant off-time method to maintain constant current
through a string of LEDs. While transistor Q2 is on, current ramps up through the inductor and LED string. A
resistor R3 senses this current and this voltage is compared to the reference voltage at FLTR2. When this
sensed voltage is equal to the reference voltage, transistor Q2 is turned off and diode D10 conducts the current
through the inductor and LEDs. Capacitor C12 eliminates most of the ripple current seen in the inductor. Resistor
R4, capacitor C11, and transistor Q3 provide a linear current ramp that sets the constant off-time for a given
output voltage.
14
Product Folder Links: LM3445
Copyright ? 2009–2013, Texas Instruments Incorporated
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3445EVM-695 | 功能描述:LM3445 1, Non-Isolated Output LED Driver Evaluation Board 制造商:texas instruments 系列:- 零件状态:有效 电流 - 输出/通道:500mA 输出和类型:1，非隔离 电压 - 输出:- 特性:可调光 电压 - 输入:90 ~ 135 VAC 所含物品:板 使用的 IC/零件:LM3445 标准包装:1 |
| LM3445M | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Triac Dimmable Offline LED Driver |
| LM3445M/NOPB | 功能描述:LED照明驱动器 RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| LM3445M/NOPB NOPB | 制造商:Texas Instruments 功能描述:TRIAC DIMMABLE LED DRIVER |
| LM3445MM | 制造商:Texas Instruments 功能描述:LED DRIVER, TRIAC DIMMABLE, 10MSOP |
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