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| 型号： | LM3445TRIACEVAL |
| 厂商： | National Semiconductor |
| 文件页数： | 23/40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
t OFF =
Finally:
1
1 V LED
K u V BUCK
f SW
(21)
K u V BUCK
L2 =
V LED 1
f SW x ' i
1 V LED
(22)
Refer to DESIGN EXAMPLE to better understand the design process.
SETTING THE LED CURRENT
The LM3445 constant off-time control loop regulates the peak inductor current (I L2 ). The average inductor current
equals the average LED current (I AVE ). Therefore the average LED current is regulated by regulating the peak
inductor current.
I L2-PK
' i L
I AVE
I L2-MIN
I L2 (t)
t ON
t OFF
t
Figure 28. Inductor Current Waveform in CCM
Knowing the desired average LED current, I AVE and the nominal inductor current ripple, Δ i L , the peak current for
an application running in continuous conduction mode (CCM) is defined as follows:
I L2-PK = I AVE + ' 2 i L
Or, the maximum, or "undimmed", LED current would then be,
I AVE(UNDIM) = I L2-PK(UNDIM) - ' 2 i L
(23)
(24)
This is important to calculate because this peak current multiplied by the sense resistor R3 will determine when
the internal comparator is tripped. The internal comparator turns the control MOSFET off once the peak sensed
voltage reaches 750 mV.
I L-PK(UNDIM) =
750 mV
R3
(25)
Current Limit : Under normal circumstances, the trip voltage on the PWM comparator would be less than or
equal to 750 mV, depending on the amount of dimming. However, if there is a short circuit or an excessive load
on the output, higher than normal switch currents will cause a voltage above 1.27V on the ISNS pin which will
trip the I-LIM comparator. The I-LIM comparator will reset the RS latch, turning off Q2. It will also inhibit the Start
Pulse Generator and the COFF comparator by holding the COFF pin low. A delay circuit will prevent the start of
another cycle for 180 μs.
VALLEY FILL CAPACITORS
Determining voltage rating and capacitance value of the valley-fill capacitors:
The maximum voltage seen by the valley-fill capacitors is:
Copyright ? 2009–2013, Texas Instruments Incorporated
Product Folder Links: LM3445
23
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相关代理商/技术参数 |
参数描述 |
|---|---|
| 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: |
| LM3447MT | 制造商:TI 制造商全称:Texas Instruments 功能描述:a Phase-Dimmable, Primary-Side Regulated LED Driver |
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