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View Full Version : Which LED driver would you choose?


rrasco
12/19/2011, 03:00 PM
I am planning a 3 pendant 108 LED fixture for my 210. I plan to run 72 royal blue, 24 neutral white, and 12 cool white bridgelux LEDs. Each pendant will have 24 RB, 8 NW, and 4 CW for a total of 36.

I intended to build my own drivers, but the price of getting PCBs made is discouraging me, so I am thinking I will just buy drivers if it is going to cost the same as building them. Ideally, two drivers would work best, one for white (neutral and cool) and one for blue, so I can just send two PWM signals via an arduino to control each color for dimming.

At any rate, which drivers would you choose and why? Cost is a factor, but I want to do it right, so that is negotiable on some level.

der_wille_zur_macht
12/19/2011, 03:06 PM
Depending on which commercial drivers you're looking at and which DIY designs you're considering, the DIY route should be significantly cheaper. Where are you getting your PCB quotes from? Typically that's not an issue, but again it depends on your design. If a driver has been designed to optimize the "fixed size" PCB services being offered by the current handful of hobby vendors in China (iteadstudio, seeedstudio, etc.) then they can be dirt dirt cheap.

Also keep in mind that an Arduino can send one signal (i.e. from one PWM pin) to multiple drivers, so even if you needed half a dozen drivers to handle all of a given color, you can control them all on the same "channel" by just connecting them all to the same PWM pin on the Arduino.

rrasco
12/19/2011, 03:13 PM
Well, the problem is, I don't know much about board houses, so when they have their 'pricing' pages, it's greek to me. I was looking at seeedstudio, but I don't understand it.

Originally I was looking at the single CAT4101 board, then I saw the triple CAT4101 board and then Fishman sent me schematics for the 8 driver board, which I can't translate to a PCB, so thus my problem begins. The only place I saw an actual price was $75 setup and $1.80~ a board, which at a 25 board min would put me around $125, just for PCBs. Then another $70~ for parts and then my labor. I can get meanwell HLG for $100~....so why bother with the build at that point?

Also, I'm aware I can run PWM to more than one driver, but for the sake of wiring, I'd like to keep it to a minimum if possible. However, that will be limited by driver availability.

der_wille_zur_macht
12/19/2011, 03:37 PM
That's why it depends a bit on design. Most of the designs I've done (including the "triple CAT4101") are targeted at the 5cm square size those places use, so, for instance, at iteadstudio, you get 10 boards for $9.90. That's 30 drivers, so 33 cents per driver.

Of course DIY'ing drivers for such a large array is nontrivial so if it's overwhelming, commercial is probably the way to go regardless of the cost/feature benefits of DIY. I'd lean towards the HLG but I don't have any direct personal experience with them so don't take my opinion as gospel.

SC Reefaholic
12/19/2011, 03:41 PM
Make it easy on yourself. Get a 185-48 for the whites at 1300 mA max per string (3) and a 240-48 for the blues a 830 mA max per string (6) and be done with it. Assuming of course you are using XP-G and XP-E LEDS.

Now if you're going with XMs and XTs then that changes everything.

rrasco
12/19/2011, 04:02 PM
Make it easy on yourself. Get a 185-48 for the whites at 1300 mA max per string (3) and a 240-48 for the blues a 830 mA max per string (6) and be done with it. Assuming of course you are using XP-G and XP-E LEDS.

Now if you're going with XMs and XTs then that changes everything.

Does that change things if I am using the bridgelux LEDs?

rrasco
12/19/2011, 04:21 PM
That's why it depends a bit on design. Most of the designs I've done (including the "triple CAT4101") are targeted at the 5cm square size those places use, so, for instance, at iteadstudio, you get 10 boards for $9.90. That's 30 drivers, so 33 cents per driver.

How did you price those board on iteadstudio? I can't find anywhere on that site to submit a PCB design or their pricing options.

SC Reefaholic
12/19/2011, 04:55 PM
Dont know the specs on those. Numbers above are based on a Cree XP-G Cool White with forward voltage of ~ 3.5 and max current of 1500 mA and a Cree XP-E Royal Blue with forward voltage of ~ 3.5 and max current of 1000 mA.

You would need to know the fV and max mA for the individual LEDs to determine how many you can run per string and how many strings per driver.

rrasco
12/19/2011, 04:56 PM
They are 3.7 fV and I believe the max current is 700mA.

rrasco
12/19/2011, 06:39 PM
I'm starting to make some sense of these numbers.

The driver's voltage divided by the fV of the LED tells me how many LEDs I can run in series and the driver's current determines how many strings I can run in parallel. So if I wanted to run strings of 12 LEDs at a fV of 3.7 I would need a 48V driver. I would then multiply the intended current (say 700ma) by the number of strings I want to determine what my current needs are. In the instance I wanted 6 strings at 700mA I would need a 4.2A driver.

If these LEDs are 700mA and I run them at 60%, that means they are running at 420mA, correct? And if I only ever intended to run the LEDs at say, 90%, which would be 630mA, I would only need a driver with a current equal to or greater than 630mA multiplied by the number of intended strings, correct?

On a side note, the LEDs are actually 3.6V, not 3.7V as I thought.

SC Reefaholic
12/19/2011, 06:45 PM
I personally would never build an LED rig where I couldnt safely run at max current and voltage. You may never intend to but you never know when an "accident" might happen and they get bumped to 100%. Could be a very expensive mistake.

But yes, your numbers are correct.

rrasco
12/19/2011, 06:49 PM
Does that mean I want to make sure I can't power the LEDs at 100%? So if I have 6 strings at 700mA max current, I should aim for a driver that has a max current of around 4A or so?

pandimus
12/19/2011, 07:03 PM
Doing a bit of research myself, but i wanna go the DIY route.. If you go to iteadstudio, and go to the open pcb section on the lower left you will see pcbprototyping. look for the 2layer green board 5cmX5cm. You can put one of the many 4101 boards in the diy driver thread on that board.. and dwzm is correct out cost savings. Only bad thing is you need an external power supply/supplys.

rrasco
12/19/2011, 07:10 PM
Well I'll be...guess that's part of the unfamiliarity I have with PCB stuff. I'm all about the DIY, I'd much rather that than spend the $165 for the off the shelf drivers I just spec'ed out. I appreciate it, that may just be my ticket.

pandimus
12/19/2011, 07:20 PM
im with you rrasco, trying to figure all this out is daunting.. I jussst. figured out how much it would cost for the boards myself, now im trying to figure out which would be the best design for me.