Go Down

Topic: Capacitors; 16V 25V 50V What's the difference? (Read 18735 times) previous topic - next topic

russellz

Note that poly capacitor's are no good for decoupling, which is the main use of a 0.1uF capacitor with the Arduino. They need to be ceramic.
Just to explain, they have lower series inductance and thus work better at high frequencies.

Russell.
Retired after 40 years as a chartered engineer working mostly with RF and analogue electronics.

dannable

work better at high frequencies.
Would you care to give rough figures? To many 16MHz is a pretty high frequency?
Beginners guide to using the Seeedstudio SIM900 GPRS/GSM Shield

Grumpy_Mike

Would you care to give rough figures? To many 16MHz is a pretty high frequency?
Where do you get 16MHz from? This is nothing to do with the frequency of the Arduino clock. 

It is simple enough poly capacitors simply do not work as supply decoupling capacitors. If you think they do then you are wrong.

dannable

Russellz said that poly caps work better at higher frequencies. I was asking what 'higher frequencies' were. I cannot see where I said that they were suitable as decoupling capacitors.
Beginners guide to using the Seeedstudio SIM900 GPRS/GSM Shield

Grumpy_Mike

Quote
Russellz said that poly caps work better at higher frequencies
No he didn't. Read reply #15 again.

Paul__B

I said "electrolytes" to prevent our resident one-upmanship-engineers here from "reminding" me that an electrolytic capacitor contains electrolyte... but I got hammered anyway for the insulator thing.....  :)
Only because you said something that was directly wrong.  No other complaints.

My rule is to make it as simple as necessary, but never by asserting something that is clearly incorrect.  That is not a valid educational principle because it can and will impede further learning, sooner or later.

krupski

#21
Jan 27, 2016, 02:15 pm Last Edit: Jan 27, 2016, 02:19 pm by Krupski
Just to explain, they have lower series inductance and thus work better at high frequencies.

Russell.
Polyester caps are best used in low to medium frequency applications such as an RC oscillator where you want decent stability and low leakage current.

For high frequency bypassing (like between VCC and COMMON of an MCU), you certainly want CERAMIC capacitors, and with as short of leads as possible... typical value is 0.1 microfarad.  Also, you typically want a larger aluminum electrolytic on the order of 50 to 100 uF (or even larger if you anticipate large, short duration current demand) in parallel with the ceramic bypass... to provide medium duration, high current supply when necessary (so that VCC doesn't sag and crash the MCU or cause a brownout reset).

The ceramic cap is great for the high frequencies, but useless at low, while the electrolytic is the opposite... together they provide effective bypassing.
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

krupski

No he didn't. Read reply #15 again.
RussellZ said "they have lower series inductance and thus work better at high frequencies" and since he quoted CERAMIC capacitors, I assume he (correctly) meant that ceramic is better for high frequencies.
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

krupski

Only because you said something that was directly wrong.  No other complaints.

My rule is to make it as simple as necessary, but never by asserting something that is clearly incorrect.  That is not a valid educational principle because it can and will impede further learning, sooner or later.

How was I wrong? Is the material between aluminum sheets not paper? Is not the paper saturated (or at least wetted) with an electrolyte of sorts?

(ever apply AC to an aluminum electrolytic and have the can explode, filling the room with really stinky smoke and small shards of "tissue paper")?  :)
Gentlemen may prefer Blondes, but Real Men prefer Redheads!

russellz

Sorry if I wasn't clear.  I was saying that ceramic capacitors have the lowest inductance, especially surface mount types.  SM ceramic types typically have inductance of the order of 0.5 to 1 nH while leaded film capacitors can have 10 to 20 nH.  So, for the same value of capacitance, the resonant frequency of the film type is likely to be about 1/4 of that of the ceramic chip.  Above the resonant frequency the effectiveness for decoupling reduces rapidly so as the frequencies you are dealing with increase you must reduce the value of the decoupling capacitor.  Hence the common use of a small value ceramic capacitor in parallel with a larger electrolytic.

As for what "higher frequencies" means, it is all relative.  For the work I used to do before retirement I used to consider frequencies over about 1 GHz as high as they need the use of different techniques.

Russell.
Retired after 40 years as a chartered engineer working mostly with RF and analogue electronics.

Paul__B

How was I wrong? Is the material between aluminum sheets not paper? Is not the paper saturated (or at least wetted) with an electrolyte of sorts?
You made the implication that you were referring to electrolytic capacitors.
Electrolytic capacitors such as the kind you described are made by taking two long, thin sheets of aluminum, separated with paper saturated with an electrolyte and rolled up into a cylinder. Each foil sheet is one terminal.
but followed it with
To make a high value, small capacitor, you have to minimize aluminum foil thickness and paper insulator thickness.

Now, when the paper insulator is very thin, it won't take much voltage to break it down and short out the capacitor.

TomGeorge

Hi,
Attached an informative application sheet.

Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

dwightthinker

When using wet polarized capacitors, like electrolytics,
it is advised to not under voltage by more than 1/2 rating..
The voltage, that you run it, at helps to maintain the oxide
layer. If the voltage is too low, the oxide tends to turn back
to conductive aluminum. It doesn't do this evenly so that
eventually it punctures and shorts the capacitor.
This isn't said to be an issue for dry polarized like tantalums.
Tantalums do age from moisture slowly leaking into the packages.
They are notorious for being smoke bombs.
I didn't read all the stuff above but one was right, it is not
the thickness of the paper in an electrolytic. It is an oxide
layer forms on the + foil. The paper is just a spacer.
Dwight

Go Up