re your babble about a constant supply voltage.

First, I could not find a curve in the WEBbed ST2221a datasheet, but on page 7 of the Allegro 'equivalent'
http://www.allegromicro.com/en/Produc...7/6277.pdf
it does show that for a Vled 0.5-2V above the LED drop the current is, for all practical purposes, constant.

Now, as so often before, when cornered, you change a nuance to make your previous statements sound 'true'.

Nobody has ever stated that a CC generator does not need a 'regulated' (Zenered) reference voltage, but hitherto your statements has bees about a "regulated supply voltage" and that is pure horsefeathers.

Erik