constant voltage drivers?

[Gomer]

So far, I have just used constant current drivers from Advanced Transformers. I am thinking of doing an even higher power setup but the only high power drivers are constant voltage. Am I understanding correctly that I would have to use resistors for these setups?

http://www.advancetransformer.com/uploads/resources/LE-6050-R05.pdf


Could someone assume (not that far of a stretch) that I am an electronic retard and show me how to hook up a Cree XR-E's to run at 700 to 1000mA?

 

[HEY HEY ITS HENDO]

Gomer, Hello an a happy new year to you ....
we are not born electronics whizzkids, some ae more passionate about it than others so dont beat yourself up!
....tell us a bit more about what your input voltage is and exactly what, or how many you will be driving

 

[Gomer]

Thanks Hendo

so, I am reading up a bit so lets see how much I fail at this LOL

I am guessing that since it is a 12V driver, I would be running a bunch of 3 LED strings in parallel? IIRC, a cree at 700ma is around 3.6V, so 3 would be 10.8V. With 1.2V to spare, to drive 700mA, you would need a 1.2V/.7A= 1.7ohm resistor? The power the resistor would need to dissipate would be .7A*1.2V= 0.84watts (so lets call it a 1watt resistor to be safe)

each LED string would be using .7*3.6*3=7.7watts.
each LED circuit would be using 7.7+.84=8.4watts
efficiency post driver is 7.7/8.4=92%?


if each string draws 0.7amps and this driver can put out 5 amps max, I can power 7x3LED strings for a total of 21x2.5=52.5watts of LED power?

Ok, reality check..did I do all that right or did I make a fatal calculation?

What happens if an LED burns out, would the LED still have the 3.6 voltage drop, or would it cause the circuit to pass 3.6+ 1.2=4.4 V which would then cause 4.4V/1.7=2.6amps (which would fry the other 2 LEDs) and 2.6*4.4=11 watts of power through a 1watt LED = smoke and flames?

Many thanks for helping me understand this