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| 型号： | LM3445M/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 20/40页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER TRIAC DIMM 14SOIC |
| 特色产品： | LM3445 TRIAC Dimmable LED Driver |
| 标准包装： | 55 |
| 系列： | PowerWise® |
| 恒定电流： | 是 |
| 拓扑： | PWM，降压（降压） |
| 输出数： | 1 |
| 内部驱动器： | 无 |
| 类型 - 次要： | 高亮度 LED（HBLED） |
| 频率： | 30kHz ~ 1MHz |
| 电源电压： | 8 V ~ 12 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-SOIC（0.154"，3.90mm 宽） |
| 供应商设备封装： | 14-SOICN |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 125°C |
| 产品目录页面： | 1285 (CN2011-ZH PDF) |
| 其它名称： | LM3445M |
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SNVS570L – JANUARY 2009 – REVISED MAY 2013
DETERMINING DUTY-CYCLE (D)
Duty cycle (D) approximately equals:
DESIGN GUIDE
V LED
V BUCK
=D= t ON + t OFF
t ON
= t ON x f SW
(4)
With efficiency considered:
1 u V LED = D
K V BUCK
(5)
For simplicity, choose efficiency between 75% and 85%.
CALCULATING OFF-TIME
The “Off-Time” of the LM3445 is set by the user and remains fairly constant as long as the voltage of the LED
stack remains constant. Calculating the off-time is the first step in determining the switching frequency of the
converter, which is integral in determining some external component values.
PNP transistor Q3, resistor R4, and the LED string voltage define a charging current into capacitor C11. A
constant current into a capacitor creates a linear charging characteristic.
i = C dv
dt
(6)
Resistor R4, capacitor C11 and the current through resistor R4 (i COLL ), which is approximately equal to V LED /R4,
are all fixed. Therefore, dv is fixed and linear, and dt (t OFF ) can now be calculated.
t OFF = C11 x 1.276V x
R4
V LED
(7)
Common equations for determining duty cycle and switching frequency in any buck converter:
f SW =
1
t OFF + t ON
D= t
= V LED
'? = t
Therefore:
t ON
ON + t OFF
t OFF
ON + t OFF
V
BUCK
(8)
D t -
f SW = t ON , and f SW = 1 OFF D
With efficiency of the buck converter in mind:
V LED
V BUCK = K u D
Substitute equations and rearrange:
(9)
(10)
V LED ·
K u V BUCK ?1
f SW =
§
¨ 1
?
1
t OFF
(11)
Off-time, and switching frequency can now be calculated using the equations above.
SETTING THE SWITCHING FREQUENCY
Selecting the switching frequency for nominal operating conditions is based on tradeoffs between efficiency
(better at low frequency) and solution size/cost (smaller at high frequency).
20
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 |
|---|---|
| LM3445MX | 制造商:NSC 制造商全称:National Semiconductor 功能描述:Triac Dimmable Offline LED Driver |
| LM3445MX/NOPB | 功能描述:板上安装温度传感器 RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
| LM3445TRIACEVAL | 功能描述:BOARD EVAL LM3445MM RoHS:否 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 |
| 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 |
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