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Electronics => Beginners => Topic started by: nus on May 01, 2019, 05:20:15 pm

Title: what is the point of tiny ceramic caps on power rails
Post by: nus on May 01, 2019, 05:20:15 pm

so i just replaced the c15 100uf cap on 3j1-2 and there is 4v of ripple on the power rail. it was all over the place before this.
probably going to replace the varistor and the ceramic cap on the line now, however i was wondering what is the point of these tiny caps, they always seem to be present on main power rails even after a larger cap

Title: Re: what is the point of tiny ceramic caps on power rails
Post by: ataradov on May 01, 2019, 05:33:38 pm

Here is a video on it

https://www.youtube.com/watch?v=BcJ6UdDx1vg (https://www.youtube.com/watch?v=BcJ6UdDx1vg)

Title: Re: what is the point of tiny ceramic caps on power rails
Post by: Richard Crowley on May 01, 2019, 05:35:56 pm

https://youtu.be/BcJ6UdDx1vg

https://youtu.be/P8MpZGjwgR0

https://youtu.be/1xicZF9glH0

Title: Re: what is the point of tiny ceramic caps on power rails
Post by: bson on May 01, 2019, 05:58:28 pm

It's there to reduce high frequency ripple because the electrolytic cap's impedance climbs quickly with frequency so it can't do it alone.

It's not technically a decoupling cap - those go across loads to reduce high frequency loop currents.