Electrolytic and non-Electrolytic capacitor?

Hi all,

I am curious abt the difference between electrolytic and non-electrolytic capacitor. I know that electrolytic cap has polarity and non-electrolytic cap don't. Also, electrolytic usually has higher capacitance values. What I don't know is in what situation do I use the more expensive electrolytic ones and when do I use the less expensive non-electrolytic cap?

Hope someone can help

Cheers,
Element7k

In the avionic field you never use electrolitic capacitors due the very poor reliability and the tendency to leak and decrease the capacitance in the apparatus subject to the low pressure you find at high altitudes.
Instead on the ground the difference is due to the maximum working temperature and from the ESR ( equivalent series resistance ) lower is better is.
Also, on the switching power supply the capacitor must work at very high frequencies and whinstand very high ripple.

Mandi

Most of the time you don't really have a choice. Over a few tens of uF you will be forced to use electrolytic types. In power audio applications, like in the x-over networks of a loudspeaker you sometimes need a capacitor of say 100uF and non-polarized. Because such caps are not easy to come by and expensive, people will use 2 polarized electrolytic caps back to back (2 -ve or 2 +ve terminals tied together) Because these caps are in series you will have to use caps with twice the value- 200uF. This will work, maybe not as good as a true non-polarized cap. In very high power audio they will use banks op these in serie and parallel to handle the AC current that will be flowing through them as the internal resistance ESR tend to heat up the caps.

Most well known cap manufacturers have selection guides to which cap to use for different applications. I know WIMA used to have a good selector with graphs and application tables. Maybe worth a search on Google

If your application calls for low leakage then electrolytics won't be a good choice.

E

Go to some capacitators manufacture site, kemet, avx, epcos....
try this **broken link removed**

In regards to power supplies, electrolitics are usually used to smooth out ripple and ceramics tend to smooth out the high frequency spikes. Sometimes you will see a combination of the two on the output of a power supply. Big 250 - 400V ceramic capacitors are usually used on the input of power supplies that are plugged directly into line neutral and ground. This helps keep some of the high frequency spiking noise from the switching of the power supply off the power line and it also helps keep some of the high frequency noise on the line out of the power supply.

In audio or in measurement applications it is sometimes neccessary to block the DC signal and only to let the AC part of an analog or digital signal pass through a circuit.
There you decouple the signal with a series capacitor (high pass filter).

Depending on key requirements such as lowest corner freqeuncy of the high pass filter, size of the capacitor, cost and maximum distortion you will have to chose eighter an elektrolytic or ceramic or a polyester type.... of capacitor.

Polarized capacitors have a quite high distortion in comparison to non polarized caps due to non linearities, especcially when reverse polarizing them. But non polarized caps grow hughe in size and are more expensive than electrolytic caps.

You will always have to make a compromize between different solutions. It is possible to combine different types of capacitors. Electrolytic caps are quite slow for high frequencies. A digital circuit for example running at 200 MHz only stabilized by a 100µF electrolytic capacitor will probably not work. The ESR of this cap and especcially the ESL will be much to high to keep the circuit stable. Then you can add some small 100nF ceramic caps close to the circuit. These components can provide high currents for a very short time. They will block peak current consumptions from the circuit. But because of the small capacity value the 100nF component can not provide the current for a long time. There the slow but bigger 100µF cap will help and will provide current if the higher current consumption will last for longer.
In high frequency range (500MHz - 4GHz) some 1nF in 0603 SMD case are added.

Hope it helps,

aOxOmOx

Hi all,

thank you all very much for all your inputs. They are very helpful.

I am trying to load an FM antenna with capacitors at the feed point so it gives me a reactance of about 60ohms. I am looking for suitable low-profile (so they will not stick out too much) capacitor. Can anyone recommend a suitable cap?

I am also bulding a foster sealy detector. I was wondering if I should use a electrolytic cap.

Any help is very much appreciated.