TLC5940 external power supply 5vdc best practice?

Heyho community, I am new to arduino, so please be patient :slight_smile:

I am a little bit helpless when it comes to external power supply, hope someone can give me a hint.
I am working currently on a rather simple LED table project with TLCs5940, capacitors, and a external power supply which should work over long periods. I did a lot of reading in these forums (know about power dissipation, capacitors, using diodes when powering) but can’t find a proper way to power my project, nor an in-depth explanation how to use 2 power supplies.

My questions:

  1. How do I hook up my an external power supply (5v 4a) in the following picture when I want to use just one (!) power supply source?
  2. How do I hook up my an external power supply (?v 4a) in the following picture when I want to use the arduino with the power jack and power the leds with the external source?
  3. Here I am really confused! Should the voltage for the LEDs be the same as the voltage given by the ardunio (5v) when I use 2 power supplies like in Question 2. (!) or does it even matter as long the voltage is high enough for the LEDs to be lit?
    To say it bluntly: How do I properly put current (Amps) into this circuit without damaging anything.

I know that I can just power my arduino over the 5v pin from an external power supply but this is not recommended. So what do you guys think is the optimal setup to power this kind of stuff? It seems there is no ‘best practice’ out there and it depends what i want achieve.
As a side note, I want to make a individual circuit board for this project in the end and I have no idea if I will encounter new problems when using one of the 2 described methods.

I hope the information helps you.
Regards,
IBelieveIHadAHat