That's how I do it. I used a 549 ohm resistor in line with a 10k pot. The resistor will limit the CAT to 1 amp maximum current. The 10k pot will allow you to lower the current from there to wherever you like, using the Analog dimming function built into the chip. You can still use PWM dimming on the CAT's enable pin to do the "sunrise/sunset" dimming stuff.
DIY LED driver for reef lighting
- Thread starter der_wille_zur_macht
- Start date
Pny
New member
Just be aware that the LEDs change their forward voltage if changing the current so you could potentially overheat the CAT if you change the current to much, since the CAT just regulates the voltage linear...
TheFishMan65
New member
Using a fixed with a pot in series is not a problem. That is the way I laid out my board. I also agree to watch the heat. Ideally all CATs off the same power supply should be about 1/2 volt above the Vf of the LED string. I planned separate supplies for white and blue. If you add green/red/UV/another color watch the CAT's temperature.
For the cat you can find the information on page 7
http://www.onsemi.com/pub_link/Collateral/CAT4101-D.PDF
pandimus
Active member
actually more referring to what dwzm, and terrehz were talking about.. not using the full 700mA I actually have the 768 resistor on, but im using a 10k trimpot.. I would like to know how people determine their led's are bright enough, once i figure that out, i can order the appropriate led's to make it permenent.
Boards came in this weekend but I'm still waiting on some parts from China to come in. I did have enough on-hand to build out one of the drivers on the board and things are working well so far. I did find one bug with the address pads for the temp chip where the ground pad didn't connect to ground. I'll have that fixed shortly on github but it was easy enough to fix by adding a jumper to the other ground pad..
I'll be able to finish testing all six drivers once the rest of my parts come in and I've made some good progress on the libraries.
der_wille_zur_macht
Team RC
Response from livestock, really. It's a bit of a black art. If you can get a PAR meter and take readings you'll know if you're in the right ballpark, but hobby-level PAR meters don't respond well to LEDs anyways.
And, assuming your 10k pot is in series with Rsense, there's no real need to switch out to the "correct" resistor unless it's for some personal reason. The bit that terahz and I were talking about relates to using PWM to chop the current down - if you're fiddling with Rsense that's not related (since, effectively, you're dimming in an analog manner).
Having an issue that i hope someone can help me with. I built some of the original 3xCAT4101 boards v1.0 and have finally got around to testing them with my LED array. Problem is that the output voltage is different across the three outputs. This leads to unequal lighting intensity. With no load, the voltages are 19.7, 19.4 and 20.
Any ideas?
Any ideas?
der_wille_zur_macht
Team RC
With no load? You mean, with no LEDs connected? The drivers aren't going to operate correctly in that manner.
What is your voltage source and what LEDs are you using?
What is your voltage source and what LEDs are you using?
der_wille_zur_macht
Team RC
In theory, 5A on the LM3409. But as you get much above 3A, component selection starts to get hard for the mosfet, diode, and inductor.
der_wille_zur_macht
Team RC
FWIW I got my hands on a burnt out driver board from an AI SOL yesterday. It uses the LM3404 chip, which is similar to the LM3409 except it has an internal MOSFET. I plan on taking some closeup photos and writing up an analysis of the design once I get some time to look at it. It's really interesting to compare a commercial driver to the ones we're producing.
I could send you the one of the drivers from an Ecoray 60 fixture. I don't think it's any different from the 30w A/C drivers on dealextreme that don't do dimming though. The Ecoray 60 has 2 drivers with 2 30 LED strings in series on each driver. Also has an A/C to 12v supply for the fan.
This is what I'm building my PT4115 drivers for. I'm drilling and cutting traces to split the strings into 5 LED strings in series, one driver per string, 12 strings per fixture. The white LED's have are 350ma with 3.7v forward voltage. The blue LED's I've tested are 350ma with 3.9v forward voltage.
I'm also adding a big heatsink inside the fixture since it only has an aluminum plate and moving the fan to the outside instead of being inside to make room for the heatsink. Should be able to run the fan much slower this way to keep things quiet.
This is what I'm building my PT4115 drivers for. I'm drilling and cutting traces to split the strings into 5 LED strings in series, one driver per string, 12 strings per fixture. The white LED's have are 350ma with 3.7v forward voltage. The blue LED's I've tested are 350ma with 3.9v forward voltage.
I'm also adding a big heatsink inside the fixture since it only has an aluminum plate and moving the fan to the outside instead of being inside to make room for the heatsink. Should be able to run the fan much slower this way to keep things quiet.
SkiFletch
New member
Sometimes I wonder if my LED array's problems came at just the right time, forcing me to do a much-needed overhaul of my tank. As I mentioned previously, I've been using the CAT4101 boards for a while with good results. Tank was happy, fish/corals happy, lots of PAR from the LED's, cool. Never bothered with PWM dimming, just did plain old hard on/off which worked for me. Of course the CAT's have the one drawback of significant heat, even when Vin adjusted to just slightly above Vout I still needed a fan in my box holding them. I have inherent mistrust for all small/cheap fans and didn't want my rig dependent on such a common point of failure, especially in a marine environment. At the time though I just rolled with it, cause what I had worked fine and I had no need to switch up.
Well, now I have the time/gumption to start messing around and am looking for "cooler" versions and saw the recent discussion about the LM3409 chips. While poking around with a pre-built LED array, I notice they use LM3404 instead of 3409. These appear to have limited current capacity of 1A but that's fine for me cause that's what I used for the CAT's. Since I'm trying to replace what I have and not re-wire my rig completely, this option is very intriguing to me. Before I start playing with the few 3404's I have now though, does anyone know if their heat production is more/less/similar to the CAT4101? The ones I have are not heat-sunk at all, just via'ed to big ground planes so I would think they don't generate all that much heat, just looking to see if anyone else has experience with them. Furthermore, can I use simiar BOM's that you guys have already developd for the 3409 for all the rest of the components, or do the 3404's use different equations to come up with R0, Rsense, If, etc etc.
A quick edit: I'm gonna start RTMFDS' to see if I can answer the last question about components myself, but hey, you may be able to save me some time
Well, now I have the time/gumption to start messing around and am looking for "cooler" versions and saw the recent discussion about the LM3409 chips. While poking around with a pre-built LED array, I notice they use LM3404 instead of 3409. These appear to have limited current capacity of 1A but that's fine for me cause that's what I used for the CAT's. Since I'm trying to replace what I have and not re-wire my rig completely, this option is very intriguing to me. Before I start playing with the few 3404's I have now though, does anyone know if their heat production is more/less/similar to the CAT4101? The ones I have are not heat-sunk at all, just via'ed to big ground planes so I would think they don't generate all that much heat, just looking to see if anyone else has experience with them. Furthermore, can I use simiar BOM's that you guys have already developd for the 3409 for all the rest of the components, or do the 3404's use different equations to come up with R0, Rsense, If, etc etc.
A quick edit: I'm gonna start RTMFDS' to see if I can answer the last question about components myself, but hey, you may be able to save me some time
