thx for answers.
Supply is from 12v PB, when charging circuit is not connected so input voltage is 10-14V.
this is white led, 4x4 array, datasheet say 13-14V, 1.4-1,5 A.
AN from Ti is interesting reading.
I know that making good driver is demand for longer work , I just want to have some simply driver just for temporary use, later I will do more development on that.
I am thinking make dc/dc 12 to 24, 1 pcs, and then 2 drivers for each 20w led ..buck. ??
Joe