Electronics > Beginners
5V regulator outputting 5.9V and more.
james_s:
--- Quote from: Simon on December 09, 2019, 07:55:33 am ---
--- Quote from: james_s on December 09, 2019, 07:42:10 am ---You really have to be careful with MLCC, many people are blissfully unaware of how dramatically the capacitance drops with DC across them. I was also not aware of this trait until it bit me a few times, fortunately in one-off hobby projects. It usually works fine to sprinkle on a bunch of 100n decoupling caps, but if you actually try to calculate the needed capacitance it will really get you if you don't account for that.
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Yea, that's why you use 25-50V parts even at 5V
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That won't help you. The reduction in capacitance is more closely related to physical package size, higher voltage rating does not really affect this. Pull up some datasheets and examine them closely and you'll see what I mean. This is generally a good habit to get into.
Simon:
Well what else do you do? i have seen some capacitors with a graph for capacitance versus voltage but few have them.
james_s:
If you want to use MLCC for DC filtering you have to find a datasheet with that graph and choose the value accordingly. If you can't find the data for the exact capacitor you are considering you ought to be able to find one for a part with the same dielectric. It's a pitfall of this type of capacitor and something to be aware of. Tantalum, electrolytic and dry polymer are other viable options.
mikerj:
--- Quote from: Simon on December 09, 2019, 05:42:39 pm ---Well what else do you do? i have seen some capacitors with a graph for capacitance versus voltage but few have them.
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The decent manufacturers will have these characteristics available somewhere, though finding them can sometimes be difficult IME. I really like Murata's "SimSurfing" web app that provides numerous characteristic graphs for every part, and also Spice models for them.
Simon:
this is a kemet part. I thought they were decent.
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