LM3448 datasheet(9/43 Pages) TI1

No. de pieza	LM3448

Descripción Electrónicos	Phase Dimmable Offline LED Driver with Integrated FET

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Fabricante Electrónico	TI1 [Texas Instruments]

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LM3448

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SNOSB51B – SEPTEMBER 2011 – REVISED NOVEMBER 2011

Figure 16. Line Voltage and Dimming Waveforms

Voltage waveforms for a simple TRIAC dimmer are shown in Figure 16. Figure 16(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).

Figure 16(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 can be referred to as the "firing angle" and is simply (180° -

θ).

Figure 16(c) shows a waveform from a 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 LM3448 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.

A bridge rectifier converts the line (mains) voltage of Figure 17(b) into a series of half-sines as shown in

Figure 17(a).

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