Capacitors - Whats the difference???

Boris

Hello,
I am geting more involved in electornic projects and was looking to purchase a nice assortment of capacitors. Here is my question. What is the difference between Ceramic Disc, Ceramic monolithic, electrolytic, film, monolythic, silver mica, tantalum. I understand that they are made out of different materials, but what is the difference in their function? What are they used for?

Paul Baker

Each material has various drawbacks and advantage to them. Depending on a particular application, a particular type would be best suited. To explain all of the pros and cons of each type would fill a small book. Rather than do that, I will list some of the parameters that are considered when choosing a type, this list is by no mean exhaustive.

Max capacitance value practically acheivable.
Tolerance (how far off the rated capacitance can a cap deviate).
Temperature Sensitivity (how much the value will change due to temperature changes).
Density (how small will a particular valued cap is)
Voltage (whats the maximum voltage that can be across the two terminals)
Leakage current (how quickly will a stored charge bleed off, this is equivalent to a resistor placed in parallel with the cap)
Cost
and there are others.

-Ceramic discs are the cheapest and aren't particulary good in any other criteria, but in non critical apps its ok.
-electrolytic can have large capacitances (Ive seen 10F caps) but most are polarized, meaning one terminal must always have a voltage higher or equal to the other terminal.
-Silver mica has good tolerances and is one of the least temperature sensitive but are fairly expensive
-Tantalum have a high density.
-Polyester are good middle of the road caps they neither suck nor excel at any of the criteria. But the range of values is more limited than other caps.

This is a very quick summery based on my experience which is not extensive, and as such there may be some points Im missing and possibly even some errors. But here are some apps I use each for:
-Ceramic when I just need a capacitor in a general range.
-Electrolytic for ripple reduction of AC to DC conversion, or temporary storage of a charge than needs a quick discharge (high wattage speakers, some DC-DC conversion circuits etc)
-Silver mica when a low tolerance is needed (timing circuits that need to be accurate, but not extremely accurate)
-Polyester when a ceramic would be used but needs to more insensitive to temperature variations.
-Tantalum for bypass capacitors to reduce supply ripple and EMI reduction.
I've never used film, monolythic or ceramic monolythic.

If you want more hard values for each look through http://dkc3.digikey.com/PDF/T051/SectE.pdf·it will give parameters for each of the types of caps (this is a 157pg pdf, the 1st 50 or so pgs are electrolytics)

Paul

Post Edited (Paul Baker) : 1/14/2005 4:55:43 PM GMT

Paul Baker

A good guideline is to get a grab bag (assorted values for a reduced price) of ceramic and another of electrolytic. And a stock of tantalum (pick a value between 4.7 to 10uF 6.3V the actual value is not critical) of the first price break (10 or 25) for bypassing digital chips, the actual value isnt critical. Hold off on other types of caps until you get a feel for what projects you work on call for, looking at various schematics on the web will provide guidance on the type of caps to use in the circuit. If you find yourself constantly ordering a particular value and type, stock up. You can get those full compliment kits, but alot of values are rarely called for in circuits and they'll just end up collecting·dust.

Paul

Gary M. Reese

Look at a lot of diagrams and see how each type is used. Thoes old radio shack hand books may be a ploace to start.

There are a ton of sites with gadgets for hobbies. They explain in detail how it works and why a certain componet was used.

Other than going to school for it like I did, this may be the best way. Hope it helps.

GaryR