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Topic: Bench power supply blew 4 of my TLC5940 ICs! (Read 1 time) previous topic - next topic

syr123

Very unfortunate, and looking for an explanation and solution for the future.

I have the following setup:

Running four daisy-chained TLC5940s from my Duemilanove a la this page: http://www.arduino.cc/playground/Learning/TLC5940

I have my 5V and ground from the Arduino board (USB bus power) running the TLCs.  I have 9 common anode RGB LEDs hooked up to the TLCs, and I had the anode of those hooked to a bench power supply sharing ground with the Arduino.

I did this because the LEDs pull about an amp of current in total.  Everything was running fine and work great until I switched off the bench supply.  It seemed to spike really high - all the LEDs went white, then went out.  When I turned it on again, nothing worked.  I swapped out the TLCs, and all was well, so I guess it fried them.

My question: 

- What happened?
- What an I do in the future to prevent it? Cap? Surge protection of some kind? Another power supply option?

I need something to supply about an amp of current at 3V to these LEDs, and I don't want it to be something that will surge and fry these TLCs!

Thanks

RuggedCircuits

How much did you pay for your power supply?  ]:D

It is common that the less-expensive type of supply will have some nasty spikes when they turn off or even turn on. I have made it a habit to physically disconnect the power wire from the supply before turning it off. If you can get into that habit too then you don't need another power supply.

--
The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected

syr123

I did not pay much, and I suspect that is what's happening.

For now, that is the strategy I was considering, but I wish I knew if there was a way to protect my ICs from it in general.

Furthermore, this is my prototype before I make a PCB for this thing, and I need a 3V @ 1 amp supply for the project that I know won't have these awful spikes!

Grumpy_Mike

There are some protection techniques here:-
http://www.thebox.myzen.co.uk/Tutorial/Protection.html

In your case I would try a chunky 5.1V Zener diode across the supply to clip any spikes.

syr123

Thanks very much for your reply, Mike.  After reading several tutorials on your site, I am going to add decoupling caps to all my TLCs, as well as putting 5.1V diodes across each of them.  Do I really need the diode on every IC to protect from spikes?

I have also decided to just use a 7805 and 7803 since my current requirements turn out to be < 1A

Grumpy_Mike

Quote
Do I really need the diode on every IC to protect from spikes?

No not on every chip, just one on the power line, and one on every line that goes outside your circuit. That is input or output lines that travel a long way.

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