Sorry to ask a question that I feel I should be able to google, but I'm kind of stuck. I have some different 5v AC/DC power supplies that I need to plug into the wall and use to power rgb LEDs. The max currents that I need to draw from these supplies are 2,4A, 1,2A, 0,9A, 0,6A, so I use one power supply 2,5A, one 1,5A (this one is variable 3-12V, I'm assuming that I get minimum 1,2A at 5v) and the rest 1A. What value capacitors do I put across 5v and gnd in these particular circumstances? I get that they should be rated for 10v as a safety, but I don't know how to get to a good number on capacitance. No datasheets available to me on the power supplies, but on the 1A supply it says 300mV ripple on the web site where I buy them. Thanks!

EDIT: Schematic

EDIT2: Updated schematic Schematic

  • \$\begingroup\$ Why do you need capacitors besides what's already in your power supplies? Draw a circuit diagram. \$\endgroup\$
    – winny
    Commented Dec 14, 2016 at 19:36
  • \$\begingroup\$ Ok I'm drawing, will take a while... I'm not sure why I need it, but the examples I have seen of these circuits typically use capacitors near the power source. I'm new to circuit design and I'm quite nervous to stick anything I made into the wall. :) \$\endgroup\$
    – Erik
    Commented Dec 14, 2016 at 19:50
  • \$\begingroup\$ The power supply should already have capacitors near the power source to regulate the voltage. \$\endgroup\$
    – 12Lappie
    Commented Dec 14, 2016 at 19:54
  • \$\begingroup\$ 300 mV is unlikely to cause any problems. Having three power supplies connected in an unknown way on the other hand is. \$\endgroup\$
    – winny
    Commented Dec 14, 2016 at 19:57
  • \$\begingroup\$ @winny Added schematic, let me know what you think! Did it really fast though, and it's my second ever attempt, so not sure I got everything right... \$\endgroup\$
    – Erik
    Commented Dec 14, 2016 at 20:58

1 Answer 1


These are regulated DC power supplies so you probably don't need additional capacitors in your circuit. The wall-wart already has capacitors built in. 300mv ripple may not be noticeable if you're simply driving an LED string- in any case that level won't destroy anything you're likely to be working with. Give it a try sans capacitors first, see if it works, worry about ripple later.


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