Driving a WLED does not always require 4 V
The popularity of white-light-emitting diodes (WLEDs) has skyrocketed, primarily because they are used to provide backlight to portable electronics displays. The common belief is that a single WLED requires a 4-V drive voltage. Since a Li-ion battery provides an average voltage of 3.6 V, the general industry consensus is that a step-up converter is required to power WLEDs from a single-cell Li-ion battery. As a result, many ICs are available for driving WLEDs, most requiring an external inductor or flying capacitors to boost the cell voltage high enough. As WLED technology continues to mature, the forward-voltage requirements continue to drop. Currently, there are many LEDs available with typical forward voltages (VF) in the 3.2- to 3.5-V range with maximum ratings at 3.7 to 4 V. The datasheets usually specify these voltages at LED currents of around 15 to 25 mA. This article discusses lower-current applications and how they affect the forward voltage of the WLED.
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