White-LED driver touts high efficiency


Posted on Mar 26, 2013

Most products use multiple LEDs to provide adequate backlight for a display. Because the LED`s brightness depends on its forward current, these multiple diodes commonly connect in series to ensure that the same current flows through each of them. You need approximately 14V to forward-bias four series-connected LEDs, starting from the nominal operating voltage, 2.7 to 4.2V, of a single-cell lithium-ion battery. Boost regulators usually provide this operating voltage. A current-sense resistor, which you insert in series with the LEDs, closes the feedback loop. However, it is important to minimize the voltage drop across this resistor to increase efficiency. Currently available integrated boost regulators commonly use a 1.24V bandgap voltage as the feedback reference, which results in 1.24V loss across the current-sense resistor, a loss that represents approximately 7% loss in efficiency.






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