The LED draws the advertised 3W at around 3.7V (0.8A), the LEDs should be operated between 3.0-3.7V. Using higher voltage than 3.7V will just produce a lot more heat without any noticable increase in brightness and at around 3V the brightness starts to drop very rapidly untill the voltage gets below the treshold voltage (about 2.3V) and the LED gets completely dark...
I got the LEDs here: [ Ссылка ] (but there are many other offers for the same LEDs, just search high power 3W LED...)
The step-down power converter module (with LM2596 chip): [ Ссылка ] (again many offers for the same or similar PCBs...).
