Can anyone explain capacitors to me?

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Hodgesaargh

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I was reading a bit about them in power supplies. Am I right in thinking the current is going along the wire and sometimes there is spikes in it which would disrupt an audio circuit and what the cap does it the current goes into the cap and the cap sort of stores it before letting it out. It then lets it out as a nice smooth wave without the spikes - the spikes have been absorbed by the caps?

I find it difficult to translate this to the caps in, say, the analogue output circuitry. Why would the audio signal need smoothed? Presumably these caps are doing something different? Cos if they smoothed the signal then the music signal would just get smoothed out wouldnt it? :confused:
 
The caps in analogue output are to block DC voltage, you want an AV volatge on output.
You description first was good, apply this to DC blocking, it stop the voltage and holds it, releasing in pulses.
Well thats my broken english explaination anyway:)
 
If you use the analogy of a dam , the ripple runs down the river into the dam and is disappaited into the mass. These resovoir caps then trickle a constant flow of current to the bits down stream. Like dams if you draw more current than they can supply you will run out . THats why resovoir caps tend to be big. Intrestingly lots of small caps will sound better than one big cap. As they can act faster when the need arrises, thats why bypassing works.
 
well I am not going to explain, as its kind of complex, but if you want ot know, buy bernard grob, basic electronics.

in audio they do 4 jobs I think, maybe more.

1. block dc, whilst passing the signal....coupling, usually plastic types: teflon, polyprop, polystyrene, polyester.
small values, higher quality

2. bypassing or decoupling, usually electrolytic, or tantalum.

3. stability, reducing high frequecies so your item does not oscillate(opposite of amplifying)
very small values....silver mica, polystyrene

4. power supply caps....energy store and smoothing, electrolytic, big, very dangerous.
 
bascially, at this moment in time, at the end of the day arrrrgh more tv glib 'in figures of speech'

caps are 2 plates of foil, rolled up, with an insulator the dielectirc, plastic, paper, etc.

now dc can't pass an insulator, but electrons flow inot the plates and onto them, then the ac, your signal reverses, so they flow back out the way they came.

this is how they appear to pass ac, but not dc, nothing ideally goes through, just in and out. odd, yes.
 
The mathematics to explain capacitors is complex (literally... it involves the square root of -1), but there is an easy to comprehend model.

Water models electricity extraordinarily well.

A pipe is equivalent to a piece of wire. Flow rate is current, pressure is voltage. The narrower the pipe, the higher its resistance and more voltage is required to maintain the same rate of flow.

A capacitor is a little different though. Chop a small section out of the pipe, and put a balloon on the end of each piece that remains, so the two contact each other, and are full of water. If you put a sudden pulse down the line, this will pass through the balloons with very little interference. If you try to pass a continuous flow through, it won't go. You can increase the voltage all you like, all that will happen eventually is that it will blow up (which capacitors do, incidentally).

You can think of a capacitor as having a resistance that varies with frequency, from almost infinite at DC to very low at high frequencies. The bigger the cap, the lower its resistance will be at AC frequencies.

Thus to explain coupling and decoupling you simply have to look at how the capacitors are connected. For decoupling (eg to keep a power rail stable), the capacitor is fitted between the power rail and ground. If a high frequency signal comes along the power rail, it will see a low-impedance path through the capacitor to ground.

AC coupling puts a capacitor in series with the signal. This is done to block DC (and thus any arising DC offset between pieces of equipment) but allow AC to pass.
 
Can anyone explain capacitors to me?
Click to expand...
The conventional model of a capacitor requires a magic type of current flowing though an insulator.

So it's probably best not to know.

Nominal capacitor equation is 'Q=CV' where Q is a charge in Coulombs, C the capacitance in Farads and V the volts on the terminals. This leads to I=CdV/dt. The current flowing 'through' a capacitor is the product of the Capacitance and the rate of change of voltage at its terminals.

Paul
 
The Bernard Grob book 'Basic Electronics' ( 8th Edition) is essential reading (as has already been mentioned) and should be given bookshelf space to anybody who is serious about learning about Electrical theory.

http://www.ibiblio.org/obp/electricCircuits/DC/DC_13.html I found this to be a very informative site for most things Electric.

A word of caution though, both of these resources are of American origin and they use American notation ( for transofmers, etc ) and also ( more sensibly ??) electron flow theory ( - to + ) for all their current, as opposed to our Conventional ( + to - ) current flow.
 

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