Go Down

Topic: How to know what 'type' of caps to use?? (Read 3028 times) previous topic - next topic

xl97

Being a complete noob.. and trying to learn to read/understand schematics a bit better..

I have a question, that may be 'dumb'.. but I have n clue how its done..and I'll never know unless I ask I guess :)

When looking at a schematic.. I see (most) will have the cap 'values' listed....

but how do you know what TYPE of capacitor to use?

ceramic? metal/poly, electrolytic, tantalum..etc..

I am using this partial piece of a schematic as an example:



I see R2 has a pot/wipe symbol meaning using a pot (and I also know the circuit/pcb a bit too..so that helped)

but for C2, C5, C6, C10.. how does one 'know' what type of caps to use?

does it matter?

Thanks..



CrossRoads

If you were an audio purist, you would use caps like those listed on page 14 of this catalog.
http://www.thetubecenter.com/files/TheTubeCenter_-_Vacuum_Tube_Catalog.pdf

However, you could use plain old ceramic capacitors for C5 & C6, and aluminum electrolytics for C10 & C2 and never notice the difference if amplifying the 8-bit PWM signal from an ATMega328 for example.
You could apply some math to the values too, see what kind of filtering is being applied. The 100uF on the output could end up limiting the bass response, so a 220uF, maybe even 470uF, could be better there.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

jraskell

Capacitors have more parameters associated with them than just their rated capacitance and max voltage rating.  In particular, all capacitors also have what are called equivalent series resistance (ESR), equivalent series Inductance (ESL), and leakage resistance.  And the different types of capacitors all have different ranges of these parameters.  They all also have different responses to temperature variations, some are very stable across wide ranges of temperatures and others have various variations that are temperature dependent.

Grumpy_Mike

In general:-
Big values you can only get as electrolytic.

Decoupling (across the supply) Ceramic for values 0.1uF and lower and electrolytic (aluminum) for values above. You could use tantalum here but they are expensive and a fire hazard.
Audio coupling - polyester, polystyrene
High stability / high frequency - Silver Mica (these are only available in small values anyway and have a negative temperature coefficient)

ESR is only important for electrolytics switching a lot of current.

James C4S

#4
Oct 31, 2011, 05:13 pm Last Edit: Oct 31, 2011, 05:25 pm by James C4S Reason: 1

Being a complete noob.. and trying to learn to read/understand schematics a bit better..

but how do you know what TYPE of capacitor to use?

Even professional engineers with years of experience don't always know what type of capacitor to choose, so don't feel bad.  There are rules of thumbs out in the industry that engineers follow which aren't true or aren't true anymore.  When it comes down to it, there are a lot of "it depends" conditions for choosing the right cap.

I've been meaning to write an article on "Capacitors for Hobbyist."

BTW, most hobby style projects can get away with just ceramics.  If audio is a concern, use C0G / NPO type ceramics.

Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

xl97

thanks guys...

some of that helped alot.  (I wasnt looking for what to use on the schematic.. but how to learn to tell for myself, in general)

to summarize.. to see if I 'got it'


1.) (It depends!)  LOL
2.) big(er) values will command/default it to be a electrolytic type
3.) 'De-coupling' caps for small values up to around 0.1uF will be 'ceramic'
4.) 'De-coupling' caps for larger values will be electrolytic (aluminum)

*** (again sorry for noob question..how do I tell a de-coupling cap vs another (Audio coupling?)? just by the placement? and overtime/experience of what the cap's purpose is?)

5.) 'Audio coupling' caps are usually polyester/polystyrene type
6.) High Stability/Freq -Silver Mica type  (never even heard of these I dont think... I have mostly been limited to whats available at RadioShack   =(   (dont laugh!)  ;)

7.) If AUDIO is a concern/focus, use: C0G / NPO type ceramics capacitors

8.) Dont feel bad many people have these problems  =)


How 'versatile' are these for swapping out?

example:

I believe C2 was 'noted' as being a SMD tantalum 100uF/10v cap..

but I dont have one of those..  (I have an electrolytic one though?  would it work.)


Is there any 'rule' or 'tip' on what can be substituted for what?  (again only type)
or as long as the 'values' match.. its interchangeable?  (which I dont think it the case...is it?)



Again thanks guys..it helps a bit

(I have a new thread coming soon. asking for help on what 'exact' components to order..  ordering form Digikey/Mouser..etc is a bit 'overwhelming to the noob out there.. (lots of choices for each part..etc)

Looking to order a few 'shift register' chips I guess..

and probably some grabs bags of caps of all values & types off ebay?? (or another suggestion?)

Thanks

James C4S


5.) 'Audio coupling' caps are usually polyester/polystyrene type
6.) High Stability/Freq -Silver Mica type  (never even heard of these I dont think... I have mostly been limited to whats available at RadioShack   =(   (dont laugh!)  ;)
7.) If AUDIO is a concern/focus, use: C0G / NPO type ceramics capacitors

#5 and #6 are the same.  If a ceramic C0G/NPO doesn't have enough capacitance (they are low capacitance but high stability) then Film capacitors (polyester / polystyrene) might be necessary.  I'd also say that C0G ceramics are a replacement for #6.

C0G/NP0 ceramics can be used in audio circuits.  (This is one of those rules of thumb I mentioned.  Many say "No Ceramics in audio!!"  You just have to avoid ceramics made with barium titanite:  Z5U, Y5V, X5R, X7R, etc.)


I believe C2 was 'noted' as being a SMD tantalum 100uF/10v cap..

Tantalum is a solid electrolytic.  In this case, if the output of the amplifier can get to 9V then a 10V tantalum is absolutely not acceptable.  Standard Tantalums need to be de-rated by 50% for reliability.  So a >18V (25V) should have been specified.

I would recommend the same de-rating for Aluminum (wet) Electrolytic caps as well.

Tantalum might have been suggested since they are looking for a high capacitance (100µF) and wanted low ESR.  Ceramic isn't an option because you'd need to use X5R (which is bad for audio.)  Tantalum generally has lower ESRs than Aluminum (and the very least have ESR stability over temperature.)
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

limescout

For basic projects, I usually just consider whether or not the capacitor must be polarized or not.  If the capacitor must be non-polar, I'll go with a ceramic.  If the schematic calls for a polar capacitor, I'll use an electrolytic.  Note that there are also non-polar electrolytics, and most non-polar caps will work where polar ones are designated. 

xl97

and on any schematic.. it wil be 100% for sure labeled as such if it needs to be polarized?

Example.. I see a + sign by C2 in the above image.. but I 'think' I see + sign on the other ones too?

How to know if it requires a polarized cap or not?

thanks

James C4S

Typically the (+) shown in schematics just confirm which direction the anode and cathode should be installed, if a polarized capacitor is used. 


and on any schematic.. it wil be 100% for sure labeled as such if it needs to be polarized?

Using the qualifiers "any" and "100%" the answer is easily: No.  The difference only exists because the nature of the capacitor type's construction (not because of inherent advantages).  So it depends on if the capacitor being used can tolerance whatever voltages will be applied to it.  E.g., if used in an amplifier where the voltage may go negative (reverse) then you probably cannot use a polarized cap.  You might see a note about not using a polarized device, but don't rely on that being stated.


How to know if it requires a polarized cap or not?

Experience and common sense. 
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

retrolefty

Quote
Typically the (+) shown in schematics just confirm which direction the anode and cathode should be installed, if a polarized capacitor is used.


I've never read of the terminals of a polarized cap called the anode and cathode terminals, what is your source for that?

James C4S


I've never read of the terminals of a polarized cap called the anode and cathode terminals, what is your source for that?

Yup, we (I work for KEMET) and there rest of the industry use anode (+) and cathode (-). 

Tantalum Datasheet, cross section on page 16 :http://bit.ly/sYkvbk

Aluminum Electrolytic application note (referred throughout as the "anode foil" and "cathode foil"):  http://bit.ly/rskblg 

Wikipedia:  http://en.wikipedia.org/wiki/Capacitor

Interesting bit of trivia (or vital information, depending on your perspective).  On aluminum electrolytic the cathode is typically marked while on tantalum the anode is marked. 
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

retrolefty

#12
Oct 31, 2011, 09:19 pm Last Edit: Oct 31, 2011, 09:21 pm by retrolefty Reason: 1
Quote
Yup, we (I work for KEMET) and there rest of the industry use anode (+) and cathode (-).  


I know about the marking of positive and/or negative terminals, but again I've never seen a reference to calling them the anode and cathode terminals, as that is normally restricted to semiconductors and vacuum tubes. So can you show us any capacitor datasheet using the the words cathode and anode for the terminals?  

I'm really not trying to be argumentative, just having been in electronics for 50+ years I can't ever recall ever reading or hearing the cap terminals using those terms.

Batteries have positive and negative terminals, but I've also never heard of them referred to as the anode and cathode terminals.

Lefty

Chagrin


Quote
Yup, we (I work for KEMET) and there rest of the industry use anode (+) and cathode (-).  


I know about the marking of positive and/or negative terminals, but again I've never seen a reference to calling them the anode and cathode terminals, as that is normally restricted to semiconductors and vacuum tubes. So can you show us any capacitor datasheet using the the words cathode and anode for the terminals?

Dude, Tantalum Datasheet, cross section on page 16 http://bit.ly/sYkvbk

retrolefty



Quote
Yup, we (I work for KEMET) and there rest of the industry use anode (+) and cathode (-).  


I know about the marking of positive and/or negative terminals, but again I've never seen a reference to calling them the anode and cathode terminals, as that is normally restricted to semiconductors and vacuum tubes. So can you show us any capacitor datasheet using the the words cathode and anode for the terminals?

Dude, Tantalum Datasheet, cross section on page 16 http://bit.ly/sYkvbk


From that link you posted, calling it the positive terminal rather then the 'anode' terminal, that is my issue. Again I would bring up the common battery terminal name usage.

Quote
Reverse Voltage
Solid tantalum capacitors are polar devices and may be permanently damaged or destroyed if connected with the wrong polarity. The
positive terminal is identified on the capacitor body by a stripe plus in some cases a beveled edge. A small degree of transient reverse
voltage is permissible for short periods per the table. The capacitors should not be operated continuously in reverse mode, even within
these limits.

Go Up