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Topic: TLC5940 and 12V Power (Read 2 times) previous topic - next topic

freddyk

Hi All

Can anyone give me some tips on where to place the capacitors on the TLC5940 so that I can use a separate 12V power supply to power LEDs?

I got pulled into this by this lesson:
http://www.arduino.cc/playground/Learning/TLC5940

It works great with low power LEDs but no luck powering LEDs that require 12V.

I have read that I need to get rid of the IREF 2.2 resistor and that makes sense to me because the higher voltage I am trying to use. 

I then read that I should use a 10uF Cap to filter the LED Power supply. At least one is required, two are preferred.  Should these go between the 12V source and the ground?  I am powering the TLC with 3.3 from the Arduino and the LEDs from a 12V.  Should I ground the 12V supply to the arduino?

And then I think I need a 1.0uF Caps to decouple the power supply.  Do I connect this between pin 20 and the ground?

I don't think I will need any resistors at all for the TLC5940.  The LEDs have their own resistors already built into the strips.

Any tips on where the capacitors go would be really helpful.

Thanks,
Fred
It would probably be safer to play with matches.

---------
Current Project: http://www.fredknack.com/jumpwall/
http://www.jumpwirevideo

Grumpy_Mike

For a start decoupling is needed, between +5 and ground and between 12V and ground.
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html

The TLC5940 can operate with a 12V supply to the chip. In fact it will operate up to 17V.

However:-
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I don't think I will need any resistors at all for the TLC5940.

Yes you need a current setting resistor.

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Should I ground the 12V supply to the arduino?

If you don't nothing will work.
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

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I have read that I need to get rid of the IREF 2.2 resistor and that makes sense to me because the higher voltage I am trying to use. 

Makes absolutely no sense to me.

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The LEDs have their own resistors already built into the strips.

That suggests they might not be suitable for driving with the TLC5940 - how much current do they take?

freddyk

Thanks Mike!

I will go through your links and tips and see if I can make any headway.

I am trying to base my project on this Brilldea design:
http://www.brilldea.com/product_LEDPainter.html

I am trying to do the same thing but with my own breadboard, ICs, capacitors and resistors.

The LEDs I have are these:
http://www.brilldea.com/product_RGBRibbon.html

I will post again when I have made some progress.

Fred





It would probably be safer to play with matches.

---------
Current Project: http://www.fredknack.com/jumpwall/
http://www.jumpwirevideo

stevethatsmyname

Hi Fred,

I am currently looking into doing a similar project with the 12V strip lights. 

Obviously the Brilldea project uses TLC5940 as a driver for the the strips so it's really a question of implementation.  It appears they have an instruction page, probably a parts list, etc,  have you tried using that as a baseline? What is going wrong with your design... you just said  it doesn't work, what doesn't work... do you have any troubleshoot tools like a DMM to figure out what is going wrong with your circuit? If not you should get a multimeter at the very least. 

One thing to note that their individual strips are a bit of a ripoff if you want a large quantity of them.  You can buy a large 5meter reel off ebay for much cheaper ($30-40 for 50 strips) 

freddyk

Thanks for your reply Steve.

I got it working!
http://youtu.be/xoxdGcm2wik

I did try to use the Brilldea design as a baseline.  That is where I got the idea that I needed some capacitors but I was not sure where to put them.  My total lack of understanding was absolutely no help  :smiley-fat:

I did get the lights working though.  I read Grumpy Mike's page about De-Coupling and tried to implement that the best I could but in the end my problem was something else I learned from Mike's power supply page that really fixed the problem.  I simply needed to have the 12V supply and the 5V supply share a ground.  That fixed it.

I am still confused about the capacitors because it works with or without them.  But my understanding from Mike's page is that they will help the overall consistency of the design.

Thanks for your advice about the ebay deals.  I think you are right.  All Brilldea sent me was a long string of lights that I had to cut up to add (hack) connectors to.  I am sure the ebay products are similar.  I can say that I am a HUGE fan of this kind of LED.  They are really bright.  I was trying to create my project with an RGB LED matrix and that was way to much work for the minimal light intensity.

Now my next power related problem is that I want to create both a 12V and 5.5V regulated power supply from one cord.  I need to split the power to supply both the low voltage boarduino and the 12V leds.  I think I 'understand' the voltage regulator circuits necessary but I am not sure if I need to use a 24V supply and then break up into 12V and 5.5V supplies or if the single 12V supply can handle both power supply circuits.  I know that this must really expose my lack of basic understanding but I am simply fishing for clues so I know what to search for. Any ideas?
It would probably be safer to play with matches.

---------
Current Project: http://www.fredknack.com/jumpwall/
http://www.jumpwirevideo

Grumpy_Mike

Use a 12V power supply, for your LEDs and then use that same supply to regulate another line down to 5V.

freddyk

Thanks for the quick answer Grumpy!  I was hoping that was the case.  I am now off to build my first power supply circuit.  Be very very :smiley-eek-blue:
It would probably be safer to play with matches.

---------
Current Project: http://www.fredknack.com/jumpwall/
http://www.jumpwirevideo

Timtomm

Hi Builders,

I'm slightly over the "Basic" Arduino connections. I have some experiences with more complicated circuits too, but now I have two questions, both are too complicated to my current knowledge.

Here is a simplified schematics of a TLC5940 based circuit (I hope the attachement will go up). All relevant information are noted. I have only two questions:
1. Which is a good value for decoupling capacitance for 12 V source (which drives all the LEDs)?
2. Which is a good value for decoupling capacitance at 5V input for the TLC5940 (this is now direclty driven by Arduiono +5V/GND pins).
(Of course, if you have any other useful hint for this, I'll be deeply appreciate your help.)

The board is a Mega2560, but I don't think, if it's relevant.

Thanks in advance for your help!

Tom

orjon

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The TLC5940 can operate with a 12V supply to the chip. In fact it will operate up to 17V.


This is incorrect! The datasheet says Vcc should be 3-5.5v with an absolute max of 6v.

Also note that whilst each output channel can sink 80mA of current, the maximum combined current that the chip can sink is 120mA.

Grumpy_Mike

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This is incorrect!

NO IT IS NOT PLEASE READ WHAT I WROTE
The TLC5940 can operate with a 12V supply to the chip.
That is with not from!

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The datasheet says Vcc should be 3-5.5v with an absolute max of 6v.

Yes and I never said otherwise.

Many chips will not allow you to sink current from a higher voltage than the power rail but this chip will let you do it for a supply up to 17V.

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the maximum combined current that the chip can sink is 120mA.

Have you read the data sheet? The maximum current is defined by many things including heat sinking on the chip.

fungus


Also note that whilst each output channel can sink 80mA of current, the maximum combined current that the chip can sink is 120mA.


Nope. That 120mA is constrained by the total power dissipation of the chip. It can't sink 120mA with high voltages.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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