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Topic: Help making a high powered RGB Lighting system for my highschool (Read 13557 times) previous topic - next topic

charliehorse55

Thanks for all the input.

As this is my third term project for my grade 12 I need a little more depth than simply buying a premade solution in order to get a good mark I will be designing my own custom PCB.  Since I will be designing the PCB anyways it's better to use an actual driver IC than mofset switching.

That Maxium IC you linked to looks like an excellent choice.

I have no experience soldering chips onto PCBs, I have mainly only used my soldering iron to fix broken cables and connect wiring between the parts in my computer. Is there a service where you can get the PCB prototyped and assembled? I would  think there is as it would be difficult if you wanted a complicated board with a lot of small ICs.

neurostar

#31
Mar 08, 2011, 03:22 am Last Edit: Mar 08, 2011, 03:36 am by neurostar Reason: 1
OK. that was it. I think you see all these drivers are basically very similar. Since designing is a part of your education, I would recommend chips from national semi or linear tech, simply because you have a tool to simulate your circuit with the chip. You can learn a lot by checking and poking signal here and there. Many of those signal are hard to measure even with good oscilloscope. Once you understand one chip, you will understand rest of them easily. Designing proper value of parts need some calculations. Write down all the equations you see from datasheets. Later you will also find all those equations are same regardless of manufactures. Start from a reference design such as evaluation kit of a chip. PCB design of switching power is also very important. Careful on the SW - diode - GND (input capacitor) which need to be short length. You want to have big GND pour bottom of those switching circuit to minimize EMI. Thermal vias around the chip is also critical. If you don't pay for your PCB, 4 layer PCB is also good idea. For current sensing resistor, check Kelvin trace.  That's what I can think of right now. I hope that helps little.

CrossRoads

@charliehorse55,
Yes there are PCB prototype and assembly houses. I don't know if that would bust your budget.
You are in the US?
You could make  a call to www.moderndevice.com in RI, see if they'd do it for you.
I don't have any means to do surface mount either, I use thruhole for what I do and struggle  hand-soldering the occasional surface mount part on a DIP adapter (actually have my wife do it, she  has better eyes than I for the really small stuff). 0.05" spacing was not too hard to do. 0.025" (4 pins in normal DIP space of 0.1"!) was very difficult.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

neurostar

SMD soldering is not difficult at all, when you have a proper PCB footprint. All you need is good magnifier. You will be amazed with how good your hands are under magnifier or low-power microscope. Instead of making one big PCB for four drivers, make four pieces. Order 5-6 PCBs, there are almost no price differences. You have something to practice. If you are still not confident with SMD soldering, send them to me as long as you are in US. I'll reflow them for free.

CrossRoads

me too? I just got a couple of MAX6921AUI with 0.025" spacing, thought I was getting MAX6921AWI with 0.05" spacing.
Need to get an adapter too.
Waiting for this to come from Thailand,
http://cgi.ebay.com/SMD-CONVERTER-ADAPTER-PCB-SOT-TO-MSOP-SIP-DIP-14_W0QQitemZ120628243230QQcategoryZ36327QQcmdZViewItemQQ_trksidZp3286.m7QQ_trkparmsZalgo%3DLVI%26itu%3DUCI%26otn%3D2%26po%3DLVI%26ps%3D63%26clkid%3D7581984690700539118
not seeing a 28 pin adapter on it.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

neurostar

Why not.. Once you get them, send me email. sooner is better.

CrossRoads

#36
Mar 08, 2011, 05:17 am Last Edit: Mar 08, 2011, 05:20 am by CrossRoads Reason: 1
Cool, thanks neurostar. Trying to find some adapter boards that aren't too expensive yet at the same time not wait a month for delivery from Thailand.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

charliehorse55


OK. that was it. I think you see all these drivers are basically very similar. Since designing is a part of your education, I would recommend chips from national semi or linear tech, simply because you have a tool to simulate your circuit with the chip. You can learn a lot by checking and poking signal here and there. Many of those signal are hard to measure even with good oscilloscope. Once you understand one chip, you will understand rest of them easily. Designing proper value of parts need some calculations. Write down all the equations you see from datasheets. Later you will also find all those equations are same regardless of manufactures. Start from a reference design such as evaluation kit of a chip. PCB design of switching power is also very important. Careful on the SW - diode - GND (input capacitor) which need to be short length. You want to have big GND pour bottom of those switching circuit to minimize EMI. Thermal vias around the chip is also critical. If you don't pay for your PCB, 4 layer PCB is also good idea. For current sensing resistor, check Kelvin trace.  That's what I can think of right now. I hope that helps little.


That's what I've been doing. Haven't been using the simulators though, just been using the reference PCB design and modifying it to my needs. I like you idea of 6 seperate PCBs, one for each PWM channel. It seems like a much nicer and neater idea.

I live in Canada but I think I will just use a PCB assembly service. While I want to keep costs down, the school recognizes that the professional equivalent of this lighting system would cost a lot of money so as long as I justify all of the costs there won't be a problem. A moderate budgetary increase to go with a PCB assembly service is easily worth saving the potential failure of the project if I have trouble with the soldering. Additionally, even if I did manage to solder the chips I am leaving to U of T Computer engineering next year and thus I won't be able to fix the board if a mistake in my soldering causes a short. Finally, if the school wants to expand the LED array it would be very easy for them to simply order another copy of my design from the supplier.

Any suggestions for a good Canadian PCB assembler?

CrossRoads

Try posting the question as a new thread, maybe a fellow Canadian can offer a suggestion;  its bound to me missed buried 3 pages down in this thread.
Also try asking the folks at dipmicro.com, or solarbotics.com, see if they can do it or offer suggestions.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

charliehorse55

Switching plans again. I found this beauty of an LED driver:

http://www.newark.com/linear-technology/lt3496ife-pbf/ic-led-drvr-tssop28/dp/07P8434

Three individual 750mA PWM outputs.

I will construct one PCB per light, and then use a terminal block to split the PWM signal from the Arduino. That way, If the lighting array needs to be expanded you can simply add another board and wire it up.

I'll also be using 30W RGB LEDs, they take 28-33V in, so I will use a +36V PSU.

Thoughts?

CrossRoads

The LEDs use 33V max, so you plan to use 36V? Seems like planned overstress to me. Something has to dissipate that extra voltage.

Pay attention on the recommendations for the unused channels also (for your future expansion).

Watch this in your PCB layout:
"The exposed pad on
the bottom of the package must be soldered to a ground
plane. This ground should then be connected to an internal
copper ground plane with thermal vias placed directly
under the package to spread out the heat dissipated by
the LT3496."
"The exposed pad of the package is the only GND terminal of
the IC and is important for thermal management of the
IC. Therefore, it is crucial to achieve a good electrical
and thermal contact between the exposed pad and the
ground plane of the board."
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

neurostar


Switching plans again. I found this beauty of an LED driver:

http://www.newark.com/linear-technology/lt3496ife-pbf/ic-led-drvr-tssop28/dp/07P8434

Three individual 750mA PWM outputs.

I will construct one PCB per light, and then use a terminal block to split the PWM signal from the Arduino. That way, If the lighting array needs to be expanded you can simply add another board and wire it up.

I'll also be using 30W RGB LEDs, they take 28-33V in, so I will use a +36V PSU.

Thoughts?


Obviously, you didn't read what I wrote carefully. LT3496 is the chip that I used in the high power RGB LED shield. Again, I already published the design of circuit. You can just use driver part of the shield. http://arduino.cc/forum/index.php/topic,51887.0.html. You can not hand-solder LT3496, it has to be reflow due to GND. You have to find someone can do it for you. If you make only three of the driver, total cost of whole thing (PCB, parts, and assembly) will be likely higher than cost of three shields.

charliehorse55

I did read what you posted quite carefully, I just didn't catch the exact chip name. I will be running 6x 30W LEDs from 6 separate PCBs.

Also, I want to design my own circuit as this is a school project and I need something for the teacher to mark.


Finally, your circuit did not implement the Open LED protection feature of the chip, which I will need with my setup as it is entirely possible that someone leaves an LED string un-attached.

Your circuit will help though, I will modify it to my needs.

Thanks.

neurostar

Open LED protection is not necessary for buck design unless you want to arbitrarily limit the output voltage. It is over voltage protection(OVP) for boost and buck-boost design. Run the circuit from LTspice, you will understand what it does. 

charliehorse55

#44
Mar 14, 2011, 03:11 am Last Edit: Mar 14, 2011, 03:12 am by charliehorse55 Reason: 1
Thanks again. I thought that it didn't make sense for buck but thanks for confirming. Makes the circuit a little simpler.

EDIT: And what is the maximum input voltage for driver? A 48V input would work great for my needs.

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