Electronics > Electronics

Using a capacitor to smooth out a power supply

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--- Quote from: jwatte on January 07, 2013, 08:28:26 PM ---
--- Quote ---are there any other downsides to using too big of a cap?

--- End quote ---

Cost and bulk are pretty big ones :-)

--- End quote ---

The small ceramic caps have very low resistance compared to larger (non-ceramic) caps. The small caps are good for providing current needed for switching bits in digital circuits. A large electrolitic cap will perform poorly compared to a 0.01 or 0.1 uF caps for this purpose.

BTW: they might have meant 100nF, which is same as 0.1uF.


Thanks for your answer.

That makes sense.

I am pretty sure it was a 100uF becuase they show a picture, and it is a decent sized electrolytic.

I think I am going to use a ceramic .1uF for this, just like I between AREF and GND on an ATmega chip.


--- Quote from: ErikY on January 09, 2013, 08:01:12 PM ---I think I am going to use a ceramic .1uF for this

--- End quote ---

You can use both 100uf and 0.1uf if you want. That will cover what I think they meant, plus what they are actually saying. (low frequency and high frequency noise).

BTW: some regulators are sensitive to excessive capacitance on the outputs and will oscillate with a too-big cap. Something to be aware of if you ever find yourself with a DC voltage rail that is ringing. I've never actually seen it happen, but many of the datasheets warn of it.


--- Quote ---I am kind of embarrassed, but I really don't know how to use an oscope, or the one she bought me in particular, came with no instructions. I am going to have to do some learning and digging.
--- End quote ---
youtube has tutorial videos for all that stuff now . . .

An oscope is basically a multi-meter, but it draws pretty graphs instead of a boring single number. The graph changes over time, letting you see how a voltage changes over time - such as with a capacitor. If you connect power to power and ground to ground, and turn the oscope on, it should 'just work' if it's a digital oscope. You may have to rotate a knob or two to shift the graph just right.

Tommy, thanks for the info.

Admin, thanks, yeah, I was able to find a ton of info on oscopes on YouTube, unfortunately, the one my wife got me is not great at all, and does a lot of really weird things, she meant well but I think I need a better one.

I hooked up mine to some basic circuits I built on a prototype board using various cps and resistors, and at the same time made the same connections to my multimeter. The oscope was really unstable, and would often just stop reading altogether.

I will say that I never really understood the value of an oscope before, but now I do.

I am going to invest in a reliable one, they really can give you so much insight to what is going on, thanks for the recommendation.

Now I just have to figure out what to buy.


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