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Author Topic: TLC5940 > Hex Inveters > Mosfets  (Read 960 times)
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Hi, I am making a xmas New Years light controller with an arduino Uno + TLC5940 + hex inverters (for the mosfets) + N channel mosfets. It works nearly perfectly however if I turn off and on a fluoro light somewhere on the same 240v power circuit as the power supply and arduino the TLC goes very very hot n fails.

Any ideas what I can do to protect it more? I've attached the schematic.


* tlc5940driver3.png (53.09 KB, 1972x2120 - viewed 81 times.)
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Hard to say without more info from perhaps an oscilloscope on the +5V and some other lines, but, assuming line noise is the issue, that single 0.1uF cap across +5V and Gnd should have something larger across it like maybe a 10uF (0.1uF and 10uF in parallel). The 10uF filters out mostly lower freq. noise while the 0.1uF with its lower internal impedance (I think) does better at filtering the higher frequencies. Check the +5V for AC ripple and DC level. A 5.1V Zener across the +5V to Gnd (in parallel with the caps) would help clamp any overvoltage spikes that might be zapping the TLC5940.
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Also put supply decoupling on the 74LS04 chips as well.
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My guess is that a transient on either the 5V supply or on one of the inputs or ground connection that is causing the TLC to latch up. What power supply are you using, and how long are the signal and ground wires between the Arduino an the TLC? A photo of your setup would help.

A larger decoupling capacitor in parallel with the 0.1uF will help deal with transients on the supply, and resistors of about 2K to 10K in series with the inputs from the Arduino will deal with transients on the inputs or on the ground connection.

btw 74LS04 inverters will pull the mosfet gates down to 0V quite effectively, but won't drive them to anywhere near +5V very well. So the mosfets may not turn on fully, which will cause them to get hot.  A 74HC04 would be better.
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Added a basic update to the schematic so far, I have a 100uF cap and a 0.1uF on the 5 and gnd lines. Quick question, do I need a resistor for the zener diode? Haven't learned those yet.

And of course I just burned up the 5th TLC, and googling around sounds like this is very common. Are they just a terrible design or something? I have 10x WS2803 as well to play with and I'm very close to ditching the TLC all together, only trouble is I have code to get the TLC5940 working with Vixen light sequencing but I am unsure about the ws2803's.

Don't have a scope yet but I'm very close to impulse buying, if anyone can point to a decent but not too expensive one...


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Not sure about a resistor for the diode, I've seen them just tied cathode (banded end) to +V and anode to Gnd. Adding a series resistor will raise the overall level of protection voltage away from 5V, depending on the resistor value.
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Ditched the tlc5940 since I blew all 5 I had up, Tried the WS2803 and omg so easssyyy. 2 wires to control, 5v, ground, iref resistor to gnd and done. Flicked fluoro lights on n off on the same circuit for the house 240v and they didn't get hot, didn't miss a beat, worked perfectly. Just need to find a way to interface it to Vixen light sequencer now and I'll be set. Why are TLC's soooo damn easy to blow? This WS2803 was setup in like 5 minutes and it didn't miss a beat the whole time whereas the TLC would have blown.

I did notice plugging 1 input from 2 WS2803's into the same hex inverter would make a weird flicker issue at times though, but that's no biggie to deal with.
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