DIY LED driver for reef lighting

[der_wille_zur_macht]

Hi Guys,
Really impressed with the work thats being done on drivers , i'm particularly interested in the driver that uses the cat4101 and have a question about the 5vin , is the 5v line from an arduino ample for say 6 of the cat4101's or would it be better to use a separate 5v supply

Thanks

Arduino's supply will likely be fine, but it will depend on what else you're using it for. If you're JUST using it for LED control, it'll be no problem. If you're trying to drive a servo at the same time, or running a ton of other stuff, there might be problems.

It'll also depend on how much input voltage you're feeding the Arduino, etc. - but really, the draw is only a few mA, so it shouldn't be a big deal.

 

[gringabot]

Arduino's supply will likely be fine, but it will depend on what else you're using it for. If you're JUST using it for LED control, it'll be no problem. If you're trying to drive a servo at the same time, or running a ton of other stuff, there might be problems.

It'll also depend on how much input voltage you're feeding the Arduino, etc. - but really, the draw is only a few mA, so it shouldn't be a big deal.

Thanks, think i'll start off using the arduino's 5V , then if i expand to do other things i'll add a separate 5V supply

 

[Taqpol]

Hey DWZM,

I took your suggestion and I am reading this thread backwards. I'm only on page 24 but I already have a question.

It seems that the 4101 drivers are the best for our situation due to the low cost, low number of parts, and high efficiency. That being said, you have to 'tune' your DC power supply to give slightly higher then the necessary voltage drop across the string of LEDs you are running, otherwise any excess voltage will be converted to heat at the IC, potentially causing damage. Did I get this all right?

In my LED thread we have been talking to Kcress about using one (or at least, fewer) AC to DC power supplies that have the better designed front end and can work all of our LED drivers at once without causing the harmonics problem. Wouldn't that complicate the 'tuning' of the power supply a lot because we would be running multiple drivers that have multiple different strings with their own voltage drops?

 

[shackscs]

DER:

For the boards that I got, is there a measurement that I should be looking at for the hole spacing to try and get a terminal block for?

Mouser has quite a few listed but I don't want to a trial and error until I get it right.

The board:

Since space may also be an issue, I am thinking about mounting the block from the bottom. This would also help with maintaining the pin out information on the front of the board.

Any suggestions?

 

[der_wille_zur_macht]

It seems that the 4101 drivers are the best for our situation due to the low cost, low number of parts, and high efficiency. That being said, you have to 'tune' your DC power supply to give slightly higher then the necessary voltage drop across the string of LEDs you are running, otherwise any excess voltage will be converted to heat at the IC, potentially causing damage. Did I get this all right?

I agree that the CAT4101 driver is probably the best choice for most people.

Yeah, you got it right regarding the adjustment, and it's more or less me being super-picky. You could probably just plug the board into a 24v supply and run it. BUT, to get the most efficient performance and have the biggest safety cushion for the IC overheating, it should be trimmed. Especially if you're using LEDs with lower drops (XP-Gs, rebels). Don't worry - it's easier than it sounds. Any of the power supplies we've talked about in this thread or elsewhere have a trimpot on them that you can turn to adjust the voltage. So you just wire everything up, then turn that pot to get the voltage you want.

In my LED thread we have been talking to Kcress about using one (or at least, fewer) AC to DC power supplies that have the better designed front end and can work all of our LED drivers at once without causing the harmonics problem. Wouldn't that complicate the 'tuning' of the power supply a lot because we would be running multiple drivers that have multiple different strings with their own voltage drops?

Nope, not really. The power factor correction isn't related to this adjustment. If you DO end up with strings with vastly different drops, you could just bunch them on their own supplies, or "live" with a few extra watts lost to heat in the driver IC.

DER:

For the boards that I got, is there a measurement that I should be looking at for the hole spacing to try and get a terminal block for?

Mouser has quite a few listed but I don't want to a trial and error until I get it right.

The board:

Since space may also be an issue, I am thinking about mounting the block from the bottom. This would also help with maintaining the pin out information on the front of the board.

Any suggestions?

The NCP3066 board was designed with a .1" spacing for the header. You probably won't find a screw terminal block in that size - my approach for that board was plain old pin headers. 3.5mm is the smallest size I've seen/used for screw terminals and they would have taken up too much room.

 

[gringabot]

i've re-read the thread again and i think i've gotten myself all confused, is the cat4101 based driver a buck or a boost configuration?

heres a summary of my plans , light will be 12 x xp-g's running at 1000ma and 12 x xr-e RB's running at 700ma , i am planning on doing a dual board based on the designs in the thread , this means i will have 2 of the dual boards, my total current requirement will be (2 x 700ma) + (2 x 1000ma) = 3.4A ,i am looking at a 24V 4.5A psu do you think this will be sufficient for my planned setup?


Thanks

 

[der_wille_zur_macht]

i've re-read the thread again and i think i've gotten myself all confused, is the cat4101 based driver a buck or a boost configuration?

Buck - it needs an input voltage higher than the desired LED voltage.

heres a summary of my plans , light will be 12 x xp-g's running at 1000ma and 12 x xr-e RB's running at 700ma , i am planning on doing a dual board based on the designs in the thread , this means i will have 2 of the dual boards, my total current requirement will be (2 x 700ma) + (2 x 1000ma) = 3.4A ,i am looking at a 24V 4.5A psu do you think this will be sufficient for my planned setup?


Thanks

That's gonna be aaaaawful white! You might want to run the blues at a higher current than the whites, or switch the ratios around or something.

A 4.5A supply should be fine for running that load.

 

[TheFishMan65]

gringabot,

I wrote this once and lost it. So here is a summary. Make sure the white have plenty of ground for cooling. At those current the white will probably run 3 volts lower than the RB and that is an awful lot of heat from what I have seen. If you can't turn down your power supply it will be even worse.

If you are lost post back and I will try and rewrite with better explanations.

 

[gringabot]

gringabot,

I wrote this once and lost it. So here is a summary. Make sure the white have plenty of ground for cooling. At those current the white will probably run 3 volts lower than the RB and that is an awful lot of heat from what I have seen. If you can't turn down your power supply it will be even worse.

If you are lost post back and I will try and rewrite with better explanations.

plan to use active cooling in the unit

using the data from the cree website (pct tool as well) the xp-g's should have a Vf in the region of 3.4@1000ma and using the xr-e datasheet the RB should have a Vf of about 3.5 @700ma, so a total of 20.4V for the whites and 21V (theoretically)

the psu i'm thinking of using is the tdk-lambda ls100-24 , here is the spec
http://uk.tdk-lambda.com/data/docs/128957632401727500_LS Sept 09.pdf


Thanks

 

[Taqpol]

Ok, I have finally read all the relevant information about 4101 drivers to ask some questions without sounding like an idiot.

DWZM's board has three 4101's on one board, and they are all controlled by one PWM signal. So if I wanted to break it out so that every 12 LEDs was on a separate PWM channel my two options would be too buy DWZM's board but only populate two of the circuits or design a new board that only had two drivers per board, correct?

My last question relates to dimming but is not driver related. Where do most people go to buy their Arduino boards? What Arduino accessories will I need to get the dimming and programming working for a LED driver. Lastly, how many PWM channels are their on a stock Arduino?

 

[gringabot]

Ok, I have finally read all the relevant information about 4101 drivers to ask some questions without sounding like an idiot.

DWZM's board has three 4101's on one board, and they are all controlled by one PWM signal. So if I wanted to break it out so that every 12 LEDs was on a separate PWM channel my two options would be too buy DWZM's board but only populate two of the circuits or design a new board that only had two drivers per board, correct?

My last question relates to dimming but is not driver related. Where do most people go to buy their Arduino boards? What Arduino accessories will I need to get the dimming and programming working for a LED driver. Lastly, how many PWM channels are their on a stock Arduino?

i've designed a 2 driver board , i could post it if you want , but be warned its probably not the best board layout (i had never used eagle until 2 weeks ago) . One of the favourite lcd's we're using in the UK is a shield from nuelectronics.com , its a nokia 3310 lcd with a joystick. The duemilanove has 6 pwm pins and the mega has 14.

HTH
John

 

[der_wille_zur_macht]

Ok, I have finally read all the relevant information about 4101 drivers to ask some questions without sounding like an idiot.

DWZM's board has three 4101's on one board, and they are all controlled by one PWM signal. So if I wanted to break it out so that every 12 LEDs was on a separate PWM channel my two options would be too buy DWZM's board but only populate two of the circuits or design a new board that only had two drivers per board, correct?

Yep, or use a different board design. It would be super easy to modify my design to have separate PWM pins for each driver, or to hack one of the drivers off the board, etc.

FWIW since most (cheap) board houses have a pretty low minimum order, you might end up with way more boards than you need anyways, so only using 2/3rds of the circuits on each board might not be the end of the world. Plus it would be more copper per IC for cooling, etc.

My last question relates to dimming but is not driver related. Where do most people go to buy their Arduino boards? What Arduino accessories will I need to get the dimming and programming working for a LED driver. Lastly, how many PWM channels are their on a stock Arduino?

The Arduino website lists all approved vendors:

http://arduino.cc/en/Main/Buy

If you're buying an official board, you should buy from one of them. In the US, Sparkfun is probably the most popular. I also like Seeedstudio and Modern Device.

For a super-basic dimming arrangement, you just need an Arduino, an RTC module (DS1307-based is the most common), and some wire running to the drivers. That's it. If you want a display and input, then you need to get an LCD and buttons or some other input method. I'm not really a fan of putting complicated UIs on little controllers so my approach would be to not bother with a display unless you really want one - you can always add it later, for instance.

There was a "post your Arduino LED sketches" thread a week or two ago that had some code that would get you started.

gringabot, go ahead and post your EAGLE files and I'm sure you'll get some good feedback!

 

[gringabot]

gringabot, go ahead and post your EAGLE files and I'm sure you'll get some good feedback!

here it is , the schematics and board file

 

[Obi-dad]

... Seeedstudio ...

slightly off-topic - but Seeedstudio has an oscilloscope for $89. I had no idea they were that inexpensive now. While I don't really need one...I have to get one. :lol:

 

[der_wille_zur_macht]

Looks good!

I made a few little tweaks, some of them might not apply if you're homebrewing the board but in case others wanted a 2-circuit layout, the tweaks might help them.

Changes:

1) Moved two vias out away from the chip a bit (for the PWM signal).
2) Shortened the board by a few mm so it's under 5cm long.
3) Added some groundplane vias around the ICs for better cooling
4) Put silkscreen labels on the headers
5) You'd drawn the dashed line in the dimension layer but left EAGLE's default line on that layer, so I collapsed the line down to the board size. Also moved it so it starts at 0,0.

 

[gringabot]

Looks good!

I made a few little tweaks, some of them might not apply if you're homebrewing the board but in case others wanted a 2-circuit layout, the tweaks might help them.

Changes:

1) Moved two vias out away from the chip a bit (for the PWM signal).
2) Shortened the board by a few mm so it's under 5cm long.
3) Added some groundplane vias around the ICs for better cooling
4) Put silkscreen labels on the headers
5) You'd drawn the dashed line in the dimension layer but left EAGLE's default line on that layer, so I collapsed the line down to the board size. Also moved it so it starts at 0,0.

Thanks, i'll download your version and learn from it, i'm actually enjoying using eagle and learning something new

 

[der_wille_zur_macht]

slightly off-topic - but Seeedstudio has an oscilloscope for $89. I had no idea they were that inexpensive now. While I don't really need one...I have to get one. :lol:

That's the color "DSO Nano" you're referring to, correct? Seems like they never have it in stock.

FWIW they also sell Jyetech's DSO kit. I like the concept of jye's scope better than the DSO Nano because it's a little more hackable. If you don't mind some obscene SMT soldering, it's only $33 in kit form. I just got one, put it together last night. It's pretty wild. Now I'm wandering around the house looking for things I can watch on it. This DSO is also available pre-assembled or partially assembled from a bunch of other vendors (Sparkfun, nkc, jyetech themselves, etc.)

 

[Taqpol]

Ok, I have a feeling I am going to have a lot more arduino questions so for the sake of not hijacking this thread I am going to move all the questions to my DIY LED build thread.


So is the DWZM/gringabot modified 4101 board a working double driver board that has more copper for cooling? Could someone post some screenshots of it currently? I have no idea how to use Eagle.

 

[der_wille_zur_macht]

Two drivers, one PWM signal, 3.5mm screw terminals, all through-hole except for the CAT4101 itself. It should work fine.

gringabot - if you have a BOM please share - the 1uF ceramic on the outputs are sometimes hard to find/expensive in through hole. Also curious if you used the two different sized cap packages on purpose.

 

[gringabot]

gringabot - if you have a BOM please share - the 1uF ceramic on the outputs are sometimes hard to find/expensive in through hole. Also curious if you used the two different sized cap packages on purpose.

Sorry , don't have a BOM, been doing this as my eagle learning experience, the 2 different size caps was a newbie error , it would have failed a DFM check

I have absolutely no problem with the design being modified to suit the requirement best.