Protect circuits against power voltage peaks

[rompelstilchen]

Hello

I want to know how to calculate the value of a bypass capaitor to protect my IC's (tlc5940)
agains voltage peaks when i turn on my scope witch is a really old crt

i found on the web someone writing :

"Lack of proper decoupling put my benchtop supply (which was attempting to deliver a constant voltage) into an unstable feedback loop with the TLC's constant current circuitry. While set for 5v, the supply was reporting voltages up to 37v, and this was likely the cause of a few burned out chips. The easiest fix is to simply put 100 to 1000uF caps between your power supply's Vcc and GND. "

but i tried many values, i still get fried IC's

can someone enlight me on this ?

source : https://effluviaofascatteredmind.bl...41-and-arduino.html?showComment=1400574694610

thx

 

[bluelasers]

I would recommend using a 5V voltage regulator and a couple ceramic 0.1uF caps for each TLC5940. The regulator should clean up the power line and take any damage caused by spikes.

What value are you using for your current resistor?

There is a max power rating for these ICs, and it varies depending on the package being use.

I do not recommend tying the current limiting resistors together.

 

[rompelstilchen]

i use 4.7k for IREF
... but it says above to use 100 to 1000µF to protect the circuit
i put a 100nF between 5v and gnd but it did not keep my IC's to fry
i only use one 5940 in my circuit (so far)

 

[bluelasers]

That resistor would set the current at 8mA per channel which should be just fine for the power limit.

Have you tried a using a linear voltage regulator?

In the datasheet, for the application example they only use a 100nF decoupling capacitor.

 

[KlausST]

Hi,

you are talking of high powerful voltage spikes.

What comes into my mind:
* Dou you have a proper power plane, so every voltage can rely on that voltage?
* Use one path for signals and other paths for power, so that the power current has no influence on the signal voltages.
* use filtering in the power paths and in the signal paths, maybe inductive or capacitive or both.
* use TVS to keep induced voltage low.

A picture or a schematic could help us to better assist you.

Hope this helps
Klaus

 

[chemelec]

Possibly Use some "MOVISTORS". (Surge Protectors)