LED assembly question

[1-3-2-4]

I'm thinking about getting a Luxeon K 8 up assembly and the Vf is 21V, anyways I was going to use a flex block driver but here is the thing I don't know if I can run two assembly (total 16 LEd's) in series.. the driver can take any voltage from 10v-32V and output a max of 48VDC I should be OK if I wire in series right?

I'm pretty sure I should be ok but I just wanted to get 2nd opinions.

 

[rumpfy]

Presumably the driver is a buck-boost design which will take a 32 volt input and give you a 42 volt output. In principle, using a 42 volt supply with two strings of 21 volt each, in series, should be OK. The only uncertainty would be that the current for each string at 21 volt would need to be the same. The data sheet for the string would possibly show the range of current at 21 volt.
Without taking a lot of care with the string current at 21 volt, you may find, in series, that one string has say 24 volt and the other string say, 19 volt, and there may be a brightness difference between the strings. A brightness difference may exist anyway if you run two strings in parallel at 21 volt. It just depends on your application/specification.
You are certainly going to get a reasonable result; you might have to fine tune for brightness by using a shunt resistor across the string with the lower current(highest volt drop).
Hope this helps.

 

[Mike odom]

Presumably the driver is a buck-boost design which will take a 32 volt input and give you a 42 volt output.

why would it have to be buck-boost and not just boost?

 

[rumpfy]

You said that the driver input voltage range was 10 volt min and 32 volt max; and the output voltage was at least 21 volt and the maximum output was 48 volt.
So for 21 volt output you need to boost at an input of 10 to 21; and for 32 volt input you need to buck for 21 volt. So I assumed that I had read the values correctly.
For a 48 volt output you would need to boost all the input voltages.
You seemed to be asking for a sanity check and I thought you would be OK do what you wanted to do; BUT just get all the information about the driver before you decided.
If you like, if you put up some driver type or model numbers, then we can check further for you.

 

[Mike odom]

Just because the chip inputs 10-32 volts, doesn't mean that's what he's building. I would think you would power it with a standard 12V or 24V supply, but either way, he wants to tie two strings in series so it's not a 21 or 42V output, just a 42V output. So feeding 10-32V to get a 42V output is a boost regulator.

 

[Mike odom]

Of course, if you want to make in universal, a buck boost would do just that, a little more complex is all.