switching regulator as a current source

[SS]

Originally posted by nine76chris
unless your planning on putting a bunch in parallel.

Just 1 LED.
http://www.lumileds.com/

[SS]

Originally posted by nine76chris
If a constant voltage is put across a LED, a constant current would flow thru it. nuff said.

This particular LED's forward voltage varies from 3.0V to 4.5V. I put 3 in series (9V to 13.5V)

[jackinnj]

Originally posted by nine76chris
And another thing, a linear regulator would be just fine because "40V supplies have plenty current to spare". I mean.. designing a 21watt constant current (SWITCHING!) supply for a LED is not worth it, and why constant current anyway? If a constant voltage is put across a LED, a constant current would flow thru it. nuff said.

it isn't correct to assume that a constant voltage impressed upon a LED will result in constant light intensity. firstly, not all VF's are equal, secondly, the current in a led is also a function of the LED temperature (didn't I point this out a few days ago?).

you can check out the Agilent or Allegro Microsystems websites for reasons to the above.

a 21 watt constant current/constant voltage supply isn't like splitting atoms -- there are even PCB layouts on some of the manufacturer's websites -- and you can have both constant current and voltage control at the same time.

[jackinnj]

Originally posted by nine76chris
Ya, my bad....I was focused on the word "LED" not "700ma". I gotta agree with Sch3mat1c......700ma is alot for a LED, unless your planning on putting a bunch in parallel. Since you got so much voltage why don't you hook em' up in series. You could daisy chain quite a few LED's on 40v.

paralleling LED's is an invitation to disaster.