High Efficiency White LED Driver Guarantees Matching LED
Brightness – Design Note 267
Dave Kim
Introduction
White LEDs are widely used in small LCD backlight
applications for simplicity, high reliability and low cost.
However, due to variations in the forward voltage drop of
white LEDs, matching the brightness becomes a major
design consideration for multiple LED applications.
Since LED brightness is proportional to current rather
than voltage, a constant-current source driving LEDs in
series should be used to ensure the same illumination
of each LED. The LTВ®1932 uses a constant-current stepup architecture that directly regulates the LED current
and guarantees a constant light intensity in each LED,
regardless of differences in their forward voltage drops.
Its unique internal current source accurately regulates
LED current even when the input voltage is higher than
the LED voltage, greatly simplifying the battery/adapter
power designs. The internal 36V switch is capable of
driving up to eight LEDs in series with 20mA of LED
current. Li-Ion LED Driver for Four White LEDs
The white LED driver shown in Figure 1 is an ideal solution for Li-Ion powered, 4-LED backlight applications.
The LT1932 and п¬Ѓve external components require less …