DIY LED driver for reef lighting

[crisaguilar]

crisaguilar,

I am not ignoring you just don't have any thoughts at the moment. If I think of something I will let you know.

There is not a lot of experience running these in parallel. If you loose another I would remove the bad one and let the singe run at 1 amp. See if you have any problems running singularly. It also seems odd that you are only getting 1.4 amps when you specified 2 amps. Maybe you are voltage limited and this damages the CATs. Do you have resistors so you can set them to 1.3-1.4 amps?

tanx you have a good point here maibe the problem is undervoltage, but in my pcb don´t have pot :thumbdown y try change the resistor if loose other cat.

 

[NanoNana]

Hey Terahz,

I just ordered enough parts for a dozen of your boards and I'll be ordering the boards soon enough. Thanks for putting in all the leg work for us!

 

[NanoNana]

And a big thanks to DWZM, kcress, Thefishman and everyone else who helped too. I don't want to forget anyone!

 

[der_wille_zur_macht]

I am working on a version of his board with no analog dimming, bigger packages for the passives, slightly larger board with bigger pours for better thermal performance, and generally oriented towards higher currents. Will report back once I have something finished.

Anyone playing with this IC should take the time to understand some of the interactions between component choice and behavior, particularly how Coff, Toff, and the difference between Vin and Vout impact frequency, which impacts choice of inductor and Cin. Minimum ripple comes into play, too. This is an extremely flexible chip but, at least on paper, it is very "picky" as well.

 

[O2Surplus]

Anyone playing with this IC should take the time to understand some of the interactions between component choice and behavior, particularly how Coff, Toff, and the difference between Vin and Vout impact frequency, which impacts choice of inductor and Cin. Minimum ripple comes into play, too. This is an extremely flexible chip but, at least on paper, it is very "picky" as well.

Hey DWZM

I've drawn up a Pcb for this chip using PWM for dimming too, but the math equations needed for parts value selection are eluding me :headwally: (may be I should have paid more attention in school, lol) I want to drive a big BridgeLux BXRA-C4500 array at 2000ma. The Led has a Vf of 25.6 and I'll drive it with a 27 volt supply. Is there any way you can help me out with the component values based on the numbers I've supplied?

 

[der_wille_zur_macht]

O2, I have been doing my math in a spreadsheet - terahz gave it to me and I made some modifications. Shoot me a pm with your email and I will send it over. I will take a stab at those numbers anyways because (obviously) I really like this stuff.

 

[der_wille_zur_macht]

Here is a starting point. I will use the datasheet naming standards.

Coff 470pF
Roff 5.49k
L 10uH
Rsense .115ohm
Cin 10uF

That gives 1.985A drive current and 343mA ripple. A 1uF output cap should get ripple around 150mA if that is too high. The fsw will be 168kHz.

I pretty much assume Ruv1 6.98k and Ruv2 49.9k since those values don't really depend on anything else in the design.

 

[NanoNana]

OK, I just tried to create some Gerber files with the v0.4 *.brd file from Terahz using Eagle 5.11...

I have no idea what I am doing! Would someone mind sending me the:

• pcbname.GTL

• pcbname.GBL

• pcbname.GTS

• pcbname.GBS

• pcbname.GTO

• pcbname.GBO

• pcbname.TXT

or just posting them online so I can order my boards?

Thanks in advance!

 

[der_wille_zur_macht]

Where are you getting your boards from? That will determine some intricacies of the format.

 

[NanoNana]

From iTead like Terahz was, I figured it best since it's his design and thats where he got his boards. I'd be willing to get them anywhere as long as I had the right files to submit. I have made quite a few circuits in my day (though none this cool) and am actually contemplating just making my own boards instead of ordering PCBs. I didn't know it was this complicated... You should be able to just send in the *.brd file and be done with it!

 

[NanoNana]

OK, I just tried to create some Gerber files with the v0.4 *.brd file from Terahz using Eagle 5.11...

I have no idea what I am doing!...

Well, I managed to figure it out.

At the bottom of the [PCB Prototyping] Green 2 Layer 5cm*5cm max -10pcs page is a link that says Eagle CAM file here. All I had to do was use their CAM instead of creating my own and it had all of the proper names that iTead requires for their PCB manufacturing. Interestingly, they also have a Eagle DRC rule file here to verify that your design meets their criteria for those of you creating your own boards.

Again, I can't thank you guys enough for all the work you have done and especially for sharing it with all of us!

 

[terahz]

I have no idea what I am doing! Would someone mind sending me the...
or just posting them online so I can order my boards?

I've added the gerbers for seeedstudio at this url:
http://joro.geodar.com/code/LM3409 v0.4/

The boards just came in today (in red). Haven't tested them yet :

BTW, 3 days after I sent the boards to seeed, I realized I should have just put the extra circuitry for the MCP4725 in there and just make it an I2C driver board with 4000+ steps for dimming. Oh well.

I should be able to test the board tomorrow, for those who are waiting.

 

[der_wille_zur_macht]

I have played with that idea too, bu I can't find a chip that I really love. The 4725 looks good though. Too bad it only has 8 available addresses. Also if you needed more than one driver per channel you'd have to hack something.

 

[NanoNana]

...3 days after I sent the boards to seeed, I realized I should have just put the extra circuitry for the MCP4725 in there and just make it an I2C driver board with 4000+ steps for dimming. Oh well.

Well, if you do change it please keep us updated. Im going to install pots on these for manual adjustment but would love to have some for PWM that dimmed smoothly!

 

[der_wille_zur_macht]

I put the lm3409 spreadsheet on the hpled google code site, hope terahz doesn't mind me sharing his modified work. Here it is:

http://hpled.googlecode.com/svn/trunk/lm3409/lm3409_component_worksheet.xls

I tried to make the instructions obvious yet still include enough info to make good component choices. As noted above, I assume the undervoltage resistors follow default values or at least are calculated seperately. Otherwise thee spreadsheet should walk you through selection of the main components. The only obvious gotcha is making sure each part has proper power and voltage ratings, package size to match your board, etc. Let me know if anyone has feedback.

 

[O2Surplus]

I tried to make the instructions obvious yet still include enough info to make good component choices. As noted above, I assume the undervoltage resistors follow default values or at least are calculated seperately. Otherwise thee spreadsheet should walk you through selection of the main components. The only obvious gotcha is making sure each part has proper power and voltage ratings, package size to match your board, etc. Let me know if anyone has feedback.

Thanks DWZM. The spreadsheet makes working out all the component values much easier!

 

[der_wille_zur_macht]

Oh, one more note on component choice. I know I said it above, but pay attention to power ratings and other related constraints on all parts. For a week or two I've been playing with high currents on two of terahz's boards using various Rsense, Roff, Cin, Cout, and inductor values to make sure I understand the circuit thoroughly before finalizing a version I will use "in production" on the tank. Tonight I managed to get the MOSFET so hot it melted it's own solder. Time to switch to a MOSFET with a higher current capacity and lower Rds.

 

[der_wille_zur_macht]

New part and we are back to being barely above room temp even at 2.6A. The part is 512-FDD4685 from Mouser. It is only rated to 40v, which is not an issue for me at 28v. But the Rds spec is waaaay better so it's burning off less power, and it is also rated for more power anyways, so the margin of safety is way better.

And at the risk of this turning into a thread chronicling my recent failures, I got the repaired 4101 boars put together today only to realize I had put 604k ohm sense resistors on, instead of 604 ohm resistors. Needless to say, the LEDs were rather dim.

 

[O2Surplus]

Hey DWZM

Thanks for the heads-up on the mosfet. I'll go ahead and add a few of those to my parts order.
I've got a batch of boards from seeed, so when they arrive I'm sure that I'll be "letting the smoke out" of more than one with this new chip before I get something that works. lol.

 

[firechild]

Having never soldered surface mount components before, I had a certain amount of difficulty. After refering to a few youtube tutorials, I figured the best method was to solder the pins with a reasonable amount of solder and then use solder wick to remove the shorts. I'm still waiting for my solder wick to arrive but this is what I have so far:

Is there a better method for those who don't have enough experience to solder the pins individually?