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| 型号： | LM3445-120VFLBK/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： | 365mA |
| 输出及类型： | 1，隔离 |
| 输出电压： | 20V |
| 特点： | 可调光，三端双向可控硅 |
| 输入电压： | 90 ~ 135VAC |
| 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 |
|---|---|
| LM3445-120VSMEV | 制造商:Texas Instruments 功能描述:Evalaution Board For TRIACE Dimmable Offline LED Driver 制造商:Texas Instruments 功能描述:LM3445, LED DRIVER, EVALUATION BOARD 制造商:Texas Instruments 功能描述:EVAL BOARD, LM3445 1A LED DRIVER; Core Chip:LM3445; Topology:Buck (Step Down); No. of Outputs:1; Output Current:1A; Input Voltage Min:8V; Input Voltage Max:12V; Kit Contents:Evaluation Board for LM3445; Input Voltage:8V to 12V |
| LM3445-120VSMEV/NOPB | 功能描述:LED 照明开发工具 LM3445-120VSM EVAL BOARD 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: |
| LM3445-208277EV/NOPB | 功能描述:LED 照明开发工具 LM3445-208277 EVAL BOARD 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: |
| LM3445-220VEVAL/NOPB | 功能描述:BOARD EVAL LM3445 220V RoHS:是 类别:编程器，开发系统 >> 过时/停产零件编号 系列:PowerWise® 标准包装:1 系列:- 传感器类型:CMOS 成像，彩色（RGB） 传感范围:WVGA 接口:I²C 灵敏度:60 fps 电源电压:5.7 V ~ 6.3 V 嵌入式:否 已供物品:成像器板 已用 IC / 零件:KAC-00401 相关产品:4H2099-ND - SENSOR IMAGE WVGA COLOR 48-PQFP4H2094-ND - SENSOR IMAGE WVGA MONO 48-PQFP |
| LM3445-220VEVAL/NOPB | 制造商:Texas Instruments 功能描述:LED Driver Eval. Board |
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