DIY LED driver for reef lighting

[der_wille_zur_macht]

Hmm I thought it was more like 3.3 volts(plus a half volt ) per Cree at 800 MA?
Well then if that's the case then I will go with a 18 volt PSU.

It depends on which Cree you're talking about. Check the datasheets for best results, and allow a bit of extra headroom for a cushion, as there are variances from LED to LED.

For instance, at 800 mA, Cree LEDs drop approximately:

XP-G: 3.25v
XP-E: 3.4v
XR-E: 3.55v

 

[jm82792]

Don't the potrans transformers have a variable voltage(by a few volts?)?
Then i could get close and make it perfect voltage wise.

 

[der_wille_zur_macht]

Yes, most "industrial" supplies like the potrans units often used for LED builds have adjustable outputs and it is definitely worthwhile to "tune" them for minimal drop.

 

[Taqpol]

Hey guys, from a DIY standpoint what power connectors and wires do you use to get from your power supplies to your drivers and then from your drivers to the LEDs? I want something that I can quick disconnect, like molex computer plugs, but I don't know if they make cords long enough for that or in the correct gauge. My cord run will be anywhere from two feet to a possible six feet depending on where I mount my drivers.

 

[jm82792]

I was thinking about using SUB D but finding the cables seems to be a total pain.
I am also looking for cables that a hobbyist can get for cheap that have a few wires that can handle LED levels of power and a few I/O signals.

 

[terahz]

I think the easiest connection is a cat6 cable. By standard it is made of 22-24awg wire which is more than enough for the <=1A current we use. The only thing that I'm not sure of are the rj45 connectors. If they can handle the current, then that's as easy as it gets.

I, personally, just use screw terminal blocks. Not "plug-and-play" but still fairly straight forward to connect and disconnect.

 

[Taqpol]

I was thinking about using SUB D but finding the cables seems to be a total pain.
I am also looking for cables that a hobbyist can get for cheap that have a few wires that can handle LED levels of power and a few I/O signals.

I used DB9 with my original build. The plugs are easy to find at Radio Shack but the cabling is definitely hard to find. I ended up going to an old computer repair shop and bought a 6 ft female/female DB9 cable. Not only is it not really long enough, but I think one of the wires inside is broken because if the cable is not positioned JUST right the blue LED string does not light up.

I think the easiest connection is a cat6 cable. By standard it is made of 22-24awg wire which is more than enough for the <=1A current we use. The only thing that I'm not sure of are the rj45 connectors. If they can handle the current, then that's as easy as it gets.

I, personally, just use screw terminal blocks. Not "plug-and-play" but still fairly straight forward to connect and disconnect.

Admittedly I only spent about ten minutes looking online for them, but I am having trouble finding female RJ45 plugs that go to bare wires at the end. I assume I should be able to find RJ45 female connectors and crimp my LED wires into them, but I don't have a crimping tool or even the slightest know how on how to crimp any of the ethernet connectors. Other then that it sounds perfect and if you could give me any more information help I would love to look into it!

I am also looking at mounting my driver boards and power supplies above the tank. If I go that route i would only have maybe two feet of cord to deal with so I might just leave the fixture cords extra long and screw them straight into the driver terminals.

 

[terahz]

This is one option is:
http://audio-video-supply.markertek.com/search?w=EZ-SnapJack+Cat6&view=grid&x=0&y=0
Another are the Neutrik NE8FDP connectors with IDC terminals on the back.

I believe all these are rated at max 1.5A, however I could only confirm it for the Neutrik ones.

Another option is to find a female/female rj45 and just use a short patch cable for one side to connect to the drivers.

Now that I've written all that I think I'll be redoing my wiring

 

[jm82792]

In my opinion the verdict is terminal screw blocks and a bunch of labels saying what wire does what.

 

[TheFishMan65]

I will have to try it again. I thought I was running .5 volts dropped on the driver an 700.

 

[hkfoot]

CAT4101 substitute

CAT4101 substitute

After a lot of background readings, I am going to try to build my first LED driver. I am looking for substitute for CAT4101 as it is hard to found one supplying this chip in Hong Kong. After some searching, I found this PT4115 from PowTech looks promising.

PT4115 Datasheet

I am a newbie in electronic, so can someone please help me to see if I can use this chip instead of CAT4101? What other components do I need in order to build a LED driver?

 

[TheFishMan65]

I did a quick look at the datasheet and it looks like a nice chip. Can't find any pricing on it:sad1:. Looks like only a few parts (and easy to find) which will be nice.

 

[der_wille_zur_macht]

It looks like a nice chip, but same thing as FishMan - I can't find pricing, much less a distributor that even has it in their catalog (checked mouser, digikey, farnell, newark, arrow, future. . . )

 

[TheFishMan65]

Really, I found what looked like a lot of suppliers in Hong Kong - oh wait that was the point

 

[hkfoot]

Really, I found what looked like a lot of suppliers in Hong Kong - oh wait that was the point

Well, I can order it online from china, it is very cheap (around 0.25 USD each). This chip seems to be very popular in asia (esp. China). Is it ok to replace the CAT4101 and what other parts should I need to drive 6 Cree XP-G LED at 700ma? Thanks.

 

[TheFishMan65]

IIRC, you need a 47uh inductor/coil and a diode, and a power supply. The regualting cap on the supply voltage is a good idea, but not required for testing if you have a good PS.

 

[hkfoot]

Thanks FishMan. How does it compare (pros & cons) with CAT4101? I will try to order some and see how it performs. Can you list the components so I can order them correctly? The datasheet does not state the value of the sense resistor for 700ma and my electronic knowledge is not good enough to understand the datasheet very well.

 

[der_wille_zur_macht]

Pros and cons? They're pretty different, but it's hard to give a generic list of pros and cons.

Both are constant current buck regulators, which means they take some arbitrary input voltage and drop it to the appropriate voltage to maintain your desired current in the LED string. The CAT4101 is a linear regulator, which means it drops the voltage by converting extra power to heat. The PT4115 is a switching regulator, which means it uses a transistor (inside the IC) and an inductor to knock the power down. It's more efficient over a wider range of inpututput ratios, but since our setups are highly controlled, that sort of flexibility isn't very important (IMHO).

The other main differentiator between LED driver ICs is dimming methodology. Luckily, both the CAT4101 and PT4115 accept analog or digital signals over a pretty wide range of frequencies, and both can dim down to a very low duty cycle.

Linear regs typically have lower parts count and easier implementation but the chip you've found is extremely simple for a switching regulator.

If you can get them for 25 cents USD each, that's a very good price and will drop the "per LED" price by a pretty fair amount. That is, assuming they're easy to work with and don't have any huge issues once you get one built. Many pages ago we were all getting excited about the ZXLD1366 chip, which strikes me as somewhat similar to this chip, but it turned out to have some pretty horrendous issues and it didn't perform nearly as well as the datasheet claimed.

It definitely looks promising enough to spend a few bucks trying out. If I could get my hands on some I'd definitely experiment. What I'd do is set up a prototype board and try out different external components - order a few different values of inductor and sense resistor, for instance, and try them out to see what happens.

The chip has an input voltage range up to 30v, so I'd start by choosing a power supply. 24v supplies are commonly used and easy to get for cheap. Next you can choose an LED count, based on the power supply voltage minus the drop the IC needs (I don't recall seeing the drop in the datasheet). Then, pick the sense resistor, diode, and inductor based on the info in the datasheet.

 

[TheFishMan65]

+1 on what DWZM said.

The equation is I = .1/R so for 700 ma you need about a .14 ohm resistor. You may want to pick something a little higher and intentionally dim it down with the dimming circuit. Then if you need a little more light you won't have to go but a new set of resistors.

 

[der_wille_zur_macht]

PS - you'd want about a .12ohm sense resistor for 700mA drive current. The formula is Iout = .1/Rs, i.e. output current equals .1 divided by the value of the sense resistor.

The datasheet specifies other components pretty clearly:

1) Input capacitor: Will depend on your power supply and how far away it is. If you're using a well regulated DC supply and it is within a few feet, you can probably use a low-value electrolytic (say, 10 - 50 uF) with low ESR.
2) Inductor: Based on the datasheet, I'd probably get 47uH and 68uH inductors with appropriate current ratings and try both.
3) Diode: Straightforward. Get a Schottky diode with the right current rating.
4) Output cap: Mentioned as optional, to reduce ripple. It would be interesting to run some math and see what the ripple will be like. At 700mA Iout, it probably will be safe for most of the HP LEDs we're running, meaning an output cap will not be required.

The device has a 1.5w max power dissipation, which is not very much. I'd take care to design the PCB to keep that in mind - large ground pours and lots of vias near the chip. Also, make sure you do a good job of soldering down the exposed ground tab.

Good luck and tell us how it goes. If it works, it looks like a good alternative for people who can't get the CAT4101 chip or don't want to use it for some reason.