TLC5940 - Arduino gets hot

Hello Community,

I'm working on this project where I want to control 108 LEDs using 7 TLC5940.
My current set up:
I have the 7 TLC5940 daisychained, powering them with the 5v from the arduino UNO. The distance between TLCs and arduino is ~40cm. The LEDs I'm of course powering with a separate power source. This external power source I'm regulating from 9v to 5v (although I just got the input i could just use the 9v - i wonder why i didn't think about that earlier). Then I have a connection in between the GND of the external power and the Arduino GND.

Using this setup I have the following problem: Even when I'm only using 4 of those TLC the voltage regulator of the ardunio (the chip in between the jack and the USB) is getting hot, like 100°C. But not instantly, it takes about 30-60 secs.

I really have no clue where the problem could be.
Next step I will do is measuring the current in the different parts of the circuit, but I would be much happier if you could give me a better advise! :slight_smile:

Carbonaudio:
I have the 7 TLC5940 daisychained, powering them with the 5v from the arduino UNO. The distance between TLCs and arduino is ~40cm. The LEDs I'm of course powering with a separate power source. This external power source I'm regulating from 9v to 5v (although I just got the input i could just use the 9v - i wonder why i didn't think about that earlier).

Be careful. If you don't dissipate the extra 4V in the regulator the TLC will have to do it instead and may overheat. Me? I'd use the regulator (or a 5V power supply).

Carbonaudio:
Using this setup I have the following problem: Even when I'm only using 4 of those TLC the voltage regulator of the ardunio (the chip in between the jack and the USB) is getting hot, like 100°C. But not instantly, it takes about 30-60 secs.

The number of TLCs doesn't matter. If there's only data lines going from the Arduino to the TLCs (ie. data, clock, etc) then each one should only add microamps of load on the Arduino regulator.

The problem isn't apparent from your description. Exactly what wires go out from the Arduino? TLC data lines, GND ... what else?

Okay then I’ll just leave the regulator. Thanks!

Well there is the Vcc. That’s the one i was thinking i would take up too much current.
So we have got the TLC data lines (SCLK, BLANK, GSCLK, XLAT) and the 5V powering the TLCs and the GND which also has a connection to the regulator.

Those lines go to the conductor board with the TLCs. I attached a picture of the circuit diagram.

Update:
I now tried to get the Vcc for the TLCs from the regulator. Everything worked almost fine. The regulator on the arduino didn't get hot (could be for the short time it was connected) but one (the last one) of four TLCs got hot. Like 50°C, then i disconnected.
For achieving that, I simply put a wire from the Vout of the 9v->5v regulator to the Vcc line and i did the same with the GND line. The GND i additionally connected with the arduino.
I don't know if that helps or makes the problem even more complicated...

I'm really thankful for every advise!

Carbonaudio:
Update:
I now tried to get the Vcc for the TLCs from the regulator. Everything worked almost fine. The regulator on the arduino didn't get hot (could be for the short time it was connected) but one (the last one) of four TLCs got hot. Like 50°C, then i disconnected.

A TLC should draw 15-30mA for itself on Vcc. 7 TLCs shouldn't stress the Arduino regulator too much, although connecting it to the external regulator isn't a bad thing.

Maybe that last chip is defective. Try connecting everything except that chip (pull the chip out of the socket).

Changing this one TLC helped.
So currently the Vcc comes from the external regulator, that way i have no problems. Should I put an Elko between the Vcc and Ground? About 0.1µF or more?

Now I noticed another strange thing. Somehow the LEDs are randomly going on and off. It looks like that they get an impulse and then all the lights change. At the beginning it's every ~10sec but after ~30sec the lights change every 2sec.
My guess would be that the 9->5v regulator has got a problem. It's also getting quite hot (but at least i know why), so maybe the voltage is getting unstable. Could that be?

I hoping that when i can solve this problem, it was the last one and I'm about to finish this project! :slight_smile:

Carbonaudio:
Changing this one TLC helped.
So currently the Vcc comes from the external regulator, that way i have no problems. Should I put an Elko between the Vcc and Ground? About 0.1µF or more?

Now I noticed another strange thing. Somehow the LEDs are randomly going on and off. It looks like that they get an impulse and then all the lights change. At the beginning it's every ~10sec but after ~30sec the lights change every 2sec.
My guess would be that the 9->5v regulator has got a problem. It's also getting quite hot (but at least i know why), so maybe the voltage is getting unstable. Could that be?

Sounds like a decoupling problem. Put lots of 0.1uF ceramic capacitors in it between GND and +5V. Use at least one per TLC and put them as close to the Vcc pin as possible. Also put them on the inputs and outputs of your regulator and a few among the anodes of your LEDs.