- Wed Dec 16, 2015 12:04 pm
#36595
To service bursty power needs, you need capacitance that probably isn't going to be small if it is going to be a film or ceramic cap. My smallest 1uf film caps have been about 8mm on a side, and 1uf isn't much for power surges.
To filter out noise on the power feed, you are generally looking at 0.1uf or smaller, which can be an extremely tiny ceramic cap. Just throwing an 0.1uf on there isn't a bad idea, but you'd need to get an oscilloscope hooked up to determine exactly what noise you have so that you can select the correct capacitor to absorb it. It's about resonance.
If you go too big on the power reserve cap, it can just be, uh, big. And the inrush current can be hard on your power supply.
ripple current rating and ESR (equivalent series resistance) are good things to look at.
There are some pretty impressive polymer electrolytics these days. heck, there are some pretty impressive regular electrolytics these days.
I Can't tell you exactly what value cap you need for your project. It might be as little as 10uf or it might be 470uf or higher. I have a 520uf OS-Con on my breadboard at the moment that is doing a great job, but it's only there because i had it. Pulled it off of a dead laptop motherboard years ago. Vanishingly small ESR.
