参数资料
型号: LM3445-120VFLBK/NOPB
厂商: National Semiconductor
文件页数: 8/40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:
已用 IC / 零件: LM3445
SNVS570L – JANUARY 2009 – REVISED MAY 2013
An RC network consisting of R1, R2, and C1 delay the turn on of the triac until the voltage on C1 reaches the
trigger voltage of the diac. Increasing the resistance of the potentiometer (wiper moving downward) increases the
turn-on delay which decreases the on-time or "conduction angle" of the triac ( θ ). This reduces the average power
delivered to the load. Voltage waveforms for a simple triac dimmer are shown in Figure 13 . Figure 13 a shows the
full sinusoid of the input voltage. Even when set to full brightness, few dimmers will provide 100% on-time, i.e.,
the full sinusoid.
(a)
(b)
DELAY
?
?
DELAY
(c)
Figure 13. Line Voltage and Dimming Waveforms
Figure 13 b shows a theoretical waveform from a dimmer. The on-time is often referred to as the "conduction
angle" and may be stated in degrees or radians. The off-time represents the delay caused by the RC circuit
feeding the triac. The off-time be referred to as the "firing angle" and is simply 180° - θ .
Figure 13 c shows a waveform from a so-called reverse phase dimmer, sometimes referred to as an electronic
dimmer. These typically are more expensive, microcontroller based dimmers that use switching elements other
than triacs. Note that the conduction starts from the zero-crossing, and terminates some time later. This method
of control reduces the noise spike at the transition.
Since the LM3445 has been designed to assess the relative on-time and control the LED current accordingly,
most phase-control dimmers, both forward and reverse phase, may be used with success.
8
Product Folder Links: LM3445
Copyright ? 2009–2013, Texas Instruments Incorporated
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