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I have some 50w HPLEDs I want to power. Any help on circuitry design will be wonderful! Answered

The specs are Vf of 15-18V and 3200ma for one and 10-12Vf with 4000ma for the other.  I want to build it cheaply and maybe use the LM350 (?) and resistors (?). I'm going to use a 350W computer power supply since I got 2 of those lying around already. What resisters would I need to use and such?  Somewhere in a data sheet I found I should use a 120 Ohm for R1 but no clue how R1's rating will effect R2 in combination. I'm a novice at these things so lay it out in dumb mans terms =)

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These are BIG beasties. You'll waste an awful lot of heat drivingthem from a standard power supply and resistors - and a PC supplyhasn't really got the rails you need available with enough output. You'dactually be better buying a driver, if you haven't got the electronicsknowledge to build a switch mode constant current drive.

Couldn't I hook up +12 (red) and +5 (yellow) rails to make 17 volts? there's plenty of amps between the 2 rails to power several...

Not really safe to do that - the rails are not rated at the same current.

You mentioned a switch mode constant current drive?  Switch mode... can you elaborate on that?  Are there any instructables supplying information on how to construct one with the ratings specified?