Comment on How to solve power supply whine with continuous dimming LED?
draz@lemmy.world 1 year agoCaps are definitely the first thing to try. To add on, the higher your frequency, the smaller caps you’ll need. At 10kHz you’ll need around 200uF of decoupling but at 50kHz you’d only need around 40uF. The smaller capacitance means you can find caps with better ESR, or just fit into a smaller space in general.
nucleative@lemmy.world 1 year ago
Thanks for typing this up! This helps me understand a lot more about what is going on.
I may have purchased too large of cap for the first try: 470uF. I bought it online so still waiting for arrival. I’ll get some in the 40uF to 200uF range for more testing
draz@lemmy.world 1 year ago
470uf should be fine - bigger is almost always better, except if you sacrifice higher ESR for it in an application that requires lower ESR. It’s pretty common to combine a large cap with higher ESR (like an Electrolytic or tantalum) with low ESR ceramic caps. That way the large cap can handle the high speed bulk C while the smaller cap can handle the high speed stuff and switching edges.
Did you make sure the cap you picked out was rated for the voltage you are working with? For hobbyist stuff it’s usually a good idea to heavily derate voltages, to avoid blowing things up. For example, if I was working with a 24V power supply, I wouldn’t nab a 25V cap; I would spring for a 35V (or even a 50V if I’m feeling particularly paranoid). You’ll see derating like this sometimes in commercial applications, and extremely frequently in military/aerospace applications.
As a rule of thumb you should always derate by at least 20%, then increase to 100% depending on how much ripple or switching the cap will see. For this application I’d probably want to derate to at least 50%