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Capacitors in general

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Corky

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Hi Everyone,

I Know theoretically how a capacitor works and i know they can hold charge and release it instantly, i also know they charge expotentially. but when i look at the majority of circuits they all have caps, i feel i know how they work but i dont know the full potential of them,

i read they can block certain frequencies but then why would they be used on a dc circuit(no waveform)? and im sure a few guys said before i should permanently have some set up on my breadboard.

how do people know what size cap to use what type (electrlytic or not), what it should be made from. all this sort of stuff confuses me becasue we dont get taught about them in this way at college.

i feel im missing out on some important electronics knowledge

any good reads would be appreciated or a few words of wisdom from you guys. so just any information on the uses of caps really :D

Cheers again
 
Go to capacitor manufacturer's websites. For instance:
tdk.com,
avx.com
kemet.com

They have dozens and dozens of "white papers" that explain to the finest detail the ins and out of capacitors.
Please note that some very large companies, like AVX produce many types of electronic components, so in their "products" tab look for capacitors.
 
Hi Schmitt,

I think i may be looking in the wrong place on the sites or its not quite what im looking for,

i found what they are made of and why that is good but not what capacitors in general are used for in a circuit.

Regards
 
Hi,

i found this "https://en.wikipedia.org/wiki/Applications_of_capacitors" i dont really like wiki but thats the basics of what im after, but why is it my college never teaches us to use them in pretty much every cicuit we have made, yet every circuit i see on the internet or in books have a few of them.

im not really sure what my question is i just feel i dont know enough about them, also people say for example " just use a 10uf cap for that, itll do th job" how do people know this? what are the calculations for the different uses.

what caps should i permanently have on my breadboard? and why :S

Regards
 
First, have a look here at this article here in the Articles section of ETO:
https://www.electro-tech-online.com/articles/the-basics-of-bypass-capacitors.513/

i know they can hold charge and release it instantly, i also know they charge expotentially
The rate at which a capacitor charges and discharges depends on the capacitance and the resistance of the circuit.
Charge and discharge are both exponential (note spelling), hold that thought about releasing energy "instantly", it may be very quick but not instant.

i read they can block certain frequencies but then why would they be used on a dc circuit(no waveform)?
The reactance of a capacitor decreases with increasing frequency, the effect that will have on the circuit depends on how the capacitor is connected in the circuit. The statement "block certain frequencies" is oversimplified to the point of being wrong and misleading.

Even in a DC circuit there are "waveforms", what about at switch-on time? There is a great big step change in voltage.
There can also be noise in the circuit, noise picked up from various electro-magnetic radiation (radios, mains wiring etc), and if you are thinking about very small signals, there is thermal noise due to the little electrons all jiggling about in the wires. (Tricky little devils they are!).

how do people know what size cap to use what type (electrlytic or not), what it should be made from
For coupling and de-coupling, capacitors are chosen so that their reactance is "low" at the lowest frequency you are interested in. A very broad and almost meaningless statement, but often there are no hard and fast rules.
However for timing circuits and tuned circuits, the capacitance value usually is quite critical.

As a generalisation, use electrolytics when the capacitance is above 1uF. Electrolytics are usually aluminium type, but tantalum can be usefull for small physical sizes. When it comes to tantalum, some people swear by them, some people swear at them. In some areas they have been rather unreliable.
Below 1uF down to a few 100pF polyester or multilayer ceramic are ok.
Low value capacitors are often single plate ceramic.

Does this help?


JimB
 
Jim B,

that was exactly what i was looking for, it explains eveything really well and the penny has dropped on this subject,

I was a bit unsure wether to post this 'question' because i wasnt sure exactly what it was i was after, but i must of worded it well enough as i got the write answer.

Cheers again.

P.S. can i pin a post to read again later somehow? or do i need to find it again?
 
Don't know how others do it, but I have a "folder" set up in my bookmarks/favorites for posts I want to reference at a future time.
 
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