I'm a beginner in electronics, and in the process of completing a homemade power supply would love to get some advice.

The power supply itself is fairly straightforward - I'm using a laptop power supply with an output of about 20V and it powers my circuit which consists of:

  • 2 fixed at 3.3V and 5.0V
  • 2 adjustable with voltage and current limit
  • and another 5.0V to power an arduino nano
  • 4 INA219 breakouts to measure each channel voltage and current
  • an arduino nano to collect the data
  • and an LCD to display voltages, currents, current limits, etc.

It all works, however, when I attach my homemade (arduino based) oscilloscope to the outputs, I'm noticing some ripple on the 3.3V and 5V channels, adding a 100uF cap improved it but didn't get rid of it, so I upped it to 1000uF which got the job done, (or at least within +-0.03V which is the margin of error of my crappy home-made oscilloscope).

So, the question is - is there any reason not to put a 1000uF cap at the outputs of these channels?

I don't have a schematic because the circuit was simple enough, so I didn't make one before implementing it.

To simplify my question further, imagine just a DC power source and a step-down switching voltage regulator, would there be any reason not to put a 1000uF capacitor on the output of the regulator?

EDIT: Added line breaks, I couldn't figure out how to do it last night. Sorry for the mess.

  • \$\begingroup\$ They didn't want to mess it up any more than it already is? \$\endgroup\$ Commented Apr 3, 2016 at 1:30
  • 2
    \$\begingroup\$ Wall of text...!! Don't you know how to create paragraphs? \$\endgroup\$ Commented Apr 3, 2016 at 2:14
  • \$\begingroup\$ Good for including full information about your question. But PLEASE learn to format it so that we can read it. Few people an read that much detail in such a huge "wall of text"! \$\endgroup\$ Commented Apr 3, 2016 at 3:56
  • \$\begingroup\$ There can be downsides - see electronics.stackexchange.com/questions/224421/… for pros and cons. \$\endgroup\$ Commented Apr 3, 2016 at 13:58

2 Answers 2


The main reasons against are

  1. inrush current

    During startup, the capacitor effectively looks like a short to the power supply, so it will need to limit the current here.

  2. "higher-than" requirements

    The +5V rail might need to be kept above the +3.3V rail all the time, even during startup and shutdown. If you add large output capacitors and the +5V rail drops faster during shutdown, then the +3.3V capacitors need to be discharged into the +5V rail to protect any dual-supply ICs. If you have a large capacitor, this needs to be a fairly beefy diode.


If your DC/DC converters are current-limited, then inrush current isn't an issue.

Be sure they are stable with a large capacitor.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.