I bought some RGB power leds, o.a. a Cree XML. The spec/description at the (Chinese) site mentioned forward voltage of 3.3-3.9V. But when driving the led at that voltage I measure much less current than expected. ~0.150mA @ 3.9V instead of ~1A for the Cree led, and something similar for other leds with a max of 700mA. I need to go above 5V to get the full max current.
Do I misunderstand the meaning of forward voltage? Or is it happening more often that leds are supplied with higher voltage drops (than described).
I planned to use a 5V power supply and a current regulator (mosfet, resistor and transistor feedback) which requires and extra voltage of ~1.2V. This does not fit if forward voltage is that high.