Hello, I'm a first time poster, occasional lurker. Done some maths on the LM317,350 and 338 to drive LEDs, was wondering how close to the ball park I am or if I'm wayyyyyy out.
I have project which requires the powering of 150 Red and 50 Blue LEDs (Luxeon Star style, 1w). I was intending on making 2 panels each of around 100 LEDs (dependant on whether less makes the maths easier and the whole project less of a balls-ache).
Red Vf = 2.0-2.6v If = 350mA (actually around 0.8w)
Blue Vf = 3.2-3.8v If = 350mA (actually around 1.2w)
I've been looking at these 3 regulators for constant current sources for the LEDs and have come to the point where I'm wondering how many I can power from one regulator using the circuit (figure 4, Page 2) of the following PDF: http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF
I'm figuring I can get around 7 on one string using the LM317 with a 37V input and 4 strings (because the LM317 can only do 1.5A) so 28 LEDs total (blue) OR 12 red (for the sake of safety) on each string and 4 strings of these, so 48 red. Blue and red on seperate regulators of course..
The LM350 can draw 3A which would effectively double that of the LM317 and would allow for 8 x 7 blue (56) or 8 x 12 Red (96)
The only reason I'd want to use the LM338 would be to keep the current I'm using well away from the max (5A) that it can supply so as to hopefully keep the temperature down.
Are there any other considerations i need to make? Obviously everything will be thermal pasted, heatsinked and fanned for cooling, but is there any risk of thermal runaway or these chips going into thermal shutdown? Do these figures seem viable on one regulator or should I be looking at splitting it up a bit more? and how big is the chunk of metal likely to be to heatsink 100 of these?
If you need any more info for a good answer, I'm happy to provide
Love you long tiem!!
Will
I have project which requires the powering of 150 Red and 50 Blue LEDs (Luxeon Star style, 1w). I was intending on making 2 panels each of around 100 LEDs (dependant on whether less makes the maths easier and the whole project less of a balls-ache).
Red Vf = 2.0-2.6v If = 350mA (actually around 0.8w)
Blue Vf = 3.2-3.8v If = 350mA (actually around 1.2w)
I've been looking at these 3 regulators for constant current sources for the LEDs and have come to the point where I'm wondering how many I can power from one regulator using the circuit (figure 4, Page 2) of the following PDF: http://www.onsemi.com/pub_link/Collateral/AND8109-D.PDF
I'm figuring I can get around 7 on one string using the LM317 with a 37V input and 4 strings (because the LM317 can only do 1.5A) so 28 LEDs total (blue) OR 12 red (for the sake of safety) on each string and 4 strings of these, so 48 red. Blue and red on seperate regulators of course..
The LM350 can draw 3A which would effectively double that of the LM317 and would allow for 8 x 7 blue (56) or 8 x 12 Red (96)
The only reason I'd want to use the LM338 would be to keep the current I'm using well away from the max (5A) that it can supply so as to hopefully keep the temperature down.
Are there any other considerations i need to make? Obviously everything will be thermal pasted, heatsinked and fanned for cooling, but is there any risk of thermal runaway or these chips going into thermal shutdown? Do these figures seem viable on one regulator or should I be looking at splitting it up a bit more? and how big is the chunk of metal likely to be to heatsink 100 of these?
If you need any more info for a good answer, I'm happy to provide
Love you long tiem!!
Will
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