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Topic: 6x TLC5940 32 rgb leds (Read 10913 times) previous topic - next topic

The chips seem to do just fine as long as I plug them in the right order with no heat.

I have a bunch of 3w rgb leds with 350ma per led and a HengFu with two 20amp 5v outputs. The r3 resistor I used a 1.5ohm 2watt. I planned on providing 20amps 5v per board which I think should be ok but I don't think my multimeter can handle that kind of current to actually test it to see how much it's pulling. I plan on having up to 6 boards per art piece. While I think it should work i'm not sure if its the best practice. From my understanding I could have a higher voltage power supply for V2  and the extra voltage will just get burned up in the FET. Would that be a better option, or would it just be less efficient?

Grumpy_Mike

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The chips seem to do just fine as long as I plug them in the right order with no heat

Never ever plug in a chip when the power is on. It is the best way to destroy them.

Ok so I have six of these boards done for a total of 96 outputs. I have tested each of these individually ok. I have hooked it up just as before except a separate power connection for vcc for the chip.

I power on all the chips, wait a few min and they are all fine and cool to touch.

I plug in the arduino that has a different power source with a shared ground and 3 of the chips fry.

So I'm not sure if a wire has came loose in my temporary setup or how to hook this up without frying the chips.

I know they are fried because I hook them up again with only vcc and ground and they are extremly hot.

I can replace the chip, hookup the arduino directly to  the board instead of a breakout boards of greyscale clock, blank, etc and the board works ok. I know you said that working with higher powered stuff complicates things but this seems more like a hookup issue than a decoupling issue.

Feel free to ask questions, I feel like this can work but i'm just missing something simple.

Grumpy_Mike

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I power on all the chips, wait a few min and they are all fine and cool to touch.

This is because they are not doing anything so no heat is generated.

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I plug in the arduino that has a different power source with a shared ground and 3 of the chips fry.

Is the code that drives the LEDs running at this point. You should not plug in circuits together with the power attached. Connect it all up and apply the power.

There are three voltage sources. The 5v that powers the chips only, the 5v that powers the output circuits, and the arduino 12v. I'm not sure why it fry's some of the chips while it should work. 50x chips just arrived in the mail, I guess I just have to play around with it.

EVP

I'm sure i had some problem similar to that when i started using tlc9540's. i solved my problem by running the arduino with the same power supply as the tlc9540 chips. I had the grounds connected and couldn't find any problem. But for some reason when i got everything using the same power supply it when away.I seemed to have problems for ages and i couldn't pin it down for days it just seemed random. It turned out to be the length of the lead to the power supply,  all the power leads in fact had to be as short as possible. It works fine now. Ive got 12 tlc9450's running. I did notice that it can seem to work on something like the night rider demo but when they were all on and pulling a lot more currant the arduino would lock up i think that was caused by the power lead lengths.

Grumpy_Mike

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I have a bunch of 3w rgb leds with 350ma per led and a HengFu with two 20amp 5v outputs. The r3 resistor I used a 1.5ohm 2watt.

Can you post a schematic of that? It seems like you are trying to pull too much power through the chip.

Here is a circuit for one of the boards and pic of a pre-hookup of the arduino. Yeah I had a feeling seperate power supplies might be a problem so I was thinking on setting up a 5v to 12v circuit for the arduino such as this > http://www.eeweb.com/blog/circuit_projects/usb-5v-to-12v-dc-dc-step-up-converter-by-lt1618 As I said before each board works individually, the main difference now is I have long leads from a breakout board for each GSCLK, blank, SCLK, GND, V1, V2. and XLat. So if i power on the chips with V1 and everything is ok, then power the arduino and some of the chips instantly fry. So the only difference is GSCLK, blank, SCLK, Xlat are on but that should not cause some of the chips to fry should it? The only other thing is the second ground that is shared being activated which might be solved with the single power supply.

I suppose I also could run everything off a single 12v/9v high current power supply but the excess voltage will be burned up in the FETS, it might not be bad as I have everything heat sinked pretty good.

I'll get another photo or vid tonight of everything hooked up

EVP

You probably need buffers on the control lines.  You get them as ic's and they are reasonably cheep. The TLC9540 chips seems to produce a lot of high frequency noise and i think it can have really strange effects when it gets onto other lines, like power. When i switch my set-up on my fm radio upstairs has a loud interference sound all over it. I think it might need shielding. I think i might need some kind of de- coupling cap over the power supply but i cant find anything that makes a difference....(Grumpy_Mike??)

Grumpy_Mike

That circuit is rather strange, I can't understand what the thinking behind it is. I am OK with constant current drive bit but not the bit that goes into the TLC chip.

Layout is important as well as supply decoupling. You need to look at things with a scope rather than just use a radio. A scope will show went things are going wrong, a radio just detects noise which will happen even when things are right.

I used the power supply from a computer and everything works great. I was even able to ramp it up to the rainbow code that uses the maximum amount of power that I will be using for hour and a half without problems.

One weird thing, some of the tlc chips get really hot while others stay cool even with the same code pumping through them. I noted that the ones that stay cool actually have internal resistance of about 200k between power and ground pins while the others stay open as I would assume it to be.

Grumpy_Mike

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One weird thing, some of the tlc chips get really hot while others stay cool even with the same code pumping through them

That doesn't sound right. Have you looked on an oscilloscope to see that the waveforms out of the hot chips are not oscillating?

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have internal resistance of about 200k between power and ground pins

You can't make meaningful measurements like this with a meter. If that measurement was made in circuit then you should measure the same because all the power and ground should be common so you will not see any difference even if there was one.

Unfortunately I do not have an oscilloscope at my disposal at this time :(

I made the measure of ~200k between power and ground pins when the chip is completely out of circuit. I'm going to buy some heatsinks for the tlc to combat the issue but I don't think it will be too big of problem since I will only run the rainbow code a fraction of the time. I should have a video of the fiber hooked up within a week or two.

So i'm just diving back into this and doing some simple code to test things but something is very weird. The regular knight rider code works fine but when I'm just trying to turn a set of leds on it seems to shift out and makes it look funky.

Here is the video http://youtu.be/66RIkmRnJkc

Code: [Select]

#include "Tlc5940.h"
int green = 32;
int blue = 0;
int red = 64;


void setup()
{

  Tlc.init();
}


void loop()
{
     Tlc.clear(); 
   
      Tlc.set(red + 0, 4095);
       Tlc.set(red + 1, 4095);
        Tlc.set(red + 2, 4095);
       
      Tlc.set(green + 0, 4095);
       Tlc.set(green + 1, 4095);
        Tlc.set(green + 2, 4095);
       
Tlc.update();
       
    delay(350);
}
     


This should just make the first three leds yellow which it does but it shouldn't change like it does. Any clues? Maybe I"m missing something simple.

Grumpy_Mike

I would say that you have a marginal signal somewhere that is on the edge of working. Without a scope to see what sort of signals you have there is not much chance of tracking it down by guessing. See if you can get one on lone.

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