DIY LED driver for reef lighting

TheFishMan65 said:
Not only this apparently the pot is a panel mount variety and goes to a connector on the board - nice kelvin connection :).
Click to expand...

That was my concern, but it appears the resistor values used for current sense are so high a couple ohms here and there from contacts, wiring etc probbaly would not make a difference. If the current sense resistors were 1 ohm or less I would say that would be a big problem.
 
Gorogk, I am trying to remember what they told me. I think the reserve stock is in Europe so it will just take a little longer. Something like that. I thought reserve was what they were holding for another company, but it was not. If in doubt call them up, they have been very help for me.
 
Bryan,
Probably true about kelvin only mattering for low ohms, but that is what the datasheet says so I at least tried to follow it on my design. I was actually more interested in the common dimming method. Any thoughts on that?
 
HV3409_populated.jpg


Have to run out for dinner, when I get back, I'll fire it up :)
 
Field report:
So the goal is to get 12 LEDs running at max 900mA (with the parts I ordered) with 48V in. Dimmable either with PWM or 5V analog voltage.
First test:
1 XRE CW, constant 5V on the EN/PWM pin (HIGH is > 1.74V, LOW is < 0.5V). 10V on the input. LED is on, a rock solid 2.9V on the LED outputs. Nothing gets hot. Tried with 48V on the input, still nothing hot. So far, so good. Measured current for the LED - ~60mA at 10V:(.
Second test:
9 XRE LEDs mixture of CW, NW and RB. 48V input, 29.9V on the output for LEDs, 120mA :(

I have not tested any dimming yet.

So it looks like the board is more or less working, but I've likely made a mistake selecting the proper components because it was supposed to be max 900mA, not 120 or 60.

Cost so far: $8 including shipping for all components except LM3409HV and terminals/headers. ICs can be found at ~$1.5 if you search around. Boards are about $1, so without terminals we're looking at ~$12 per board, and possibly ~$15 with terminals.

This weekend I'll be troubleshooting to figure out what's wrong with the current setting and will try both dimming methods.
 
Field Report 2:
So the first mistake I found was that my Rsns (R1) was 0.1 Ohms instead of 0.22Ohms. Good thing I had a few extra, so I added another resistor there (making a small tee pee in the process :) ). Then the Vadj pin was supposed to be powered by an internal source to 1.24V, but I suspect that my voltage divider messed that up because it was measuring ~0.15V which would explain the low current. So I decided to proceed with analog dimming, which would set the voltage properly on that pin.

So I set the jumpers for analog dining, wire a 5V power source to the ADJ pin and hit the power button. Next thing I know, I'm blinded...
LM3409_analog_working.jpg

(That string is 3 RB, 3 CW and the rest NWs).
I look at the multimeter to see the current: 860mA! Hooray! I quickly remove the second Rsns resistor to the previous 0.1 Ohms, just to see what happens: 2A :D.

For PWM, I'm thinking that until the Vadj pin is completely disconnected, the max current will be set to something very low so PWM will work only on that current.

BTW now that I know these work, I have a few extra boards if anyone is interested, send me a PM. I'll test PWM later today and make fixes to the design, than I'll post the eagle files and BOM.

THz
 
Great effort on this everyone. Let me just tell you that I spent whole day reading from page #1 till about page 50.. :) then I decided to get right to the end to see what's happening in 2011.. :)

Quick question:

Let's say that one driver will drive only 3 LEDs at 12V , 1.5A can I have a power supply that's let say 42V 6A and run 3 of those drivers on the same power supply? since drivers will be connected in series they would each get 42/3 V , right or wrong?
 
I am not sure you could do that with the CAT4101, I assume that is the one you are talking about. It would try and get the same current through all the strings PWMs would not work. I really want to say a solid no, but there might be a way to make it work. But I think it would create more trouble than it is worth.
 
Thanks for the input TheFishman.
Let me try to explain. I would like to do real sunrise,full sun, sunset in such way that my leds would start dim on from left of the tank all the way till the right side of the thank. Let's say we are facing tank from the front. I know that I need lots of drivers in order to do that but question is how would I reduce number of Power supplies required. I'm just thinking out loud here.
 
Get one large 24 volt supply with lots of amps. Then you can run lots of drivers off of one supply. However if you have several strings with different voltages (LED types) you will be better with several supplies as you can make the design use less enrgy and run cooler.
 
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