Facebook | Solarsciencegroup Led Lighting: High-Brightness LEDs: Input Voltage and Forward Voltage

Facebook | Solarsciencegroup Led Lighting: High-Brightness LEDs: Input Voltage and Forward Voltage
Sources of input voltage for LED arrays come from batteries or
power supplies that have a certain tolerance. An automotive
battery, for example, may supply 8V to 16V depending on the load
and the age of the battery. The "silver box" power supply inside a
desktop CPU may supply 12V ±10%.
High-brightness (HB) LEDs also give a range of forward voltage.
A typical HB LED might be characterized at a forward current
of 350 mA. The forward voltage of the LED when IF = 350 mA is
specified with a range that includes a typical value as well as
over-temperature maximum and minimum values. To ensure that
a true constant current is delivered to each LED in an array, the
power topology must be able to deliver an output voltage equal
to the sum of the maximum forward voltages of every device
placed in the string.
Manufacturers bin their devices for color, brightness, and
forward voltage. Binning for all three characteristics is
expensive, and forward voltage is often the specification that
is allowed to vary the most. Adding this to the shift in forward
voltage as the LED die temperature changes gives rise to the
need for constant-current regulators that have a wide range of
output voltage.
Constant