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Discussion in 'General Electronics Discussion' started by Dipali2014, Feb 29, 2016.

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  1. Dipali2014


    Feb 29, 2016
    As per theory, a capacitor blocks DC signal. How it works, when we use capacitors in DC circuit. I'm new in electronics so please help me.
    Last edited by a moderator: Feb 29, 2016
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Please explain in more detail your question. A capacitor can be used in many ways within a DC circuit. Which one do you refer to?
  3. TeslaCoil


    Mar 1, 2016
    As a novice - Although it's said that it blocks DC and lets AC through - that's just to simply how a capacitor works in series in circuit.
    In reality, it doesn't let anything through as such. The two pins of the capacitor are electrically isolated.
    Think of a simple circuit - connecting a capacitor across a battery. If you measured the current in the circuit at the point of connecting the two items together, then current would flow - but only until the capacitor has fully charged. Then current stops flowing - i.e. it is blocking DC.
    If you replaced the battery with an ac source, then current would appear to be continually flowing because the AC is alternating the direction of current flow - i.e. - charging and discharging the capacitor. So AC appears to pass.

    In practice - if you have a signal source that is AC, but has some dc too (moving the AC relative zero to a higher voltage) then that extra DC may cause issues - as it's only the AC signal that you want. If you pass that signal through a capacitor in series, then the DC element is effectively removed. - Just leaving the AC signal.
  4. Gryd3


    Jun 25, 2014
    Try to think of the capacitor as if it has a movable plate inside attached to a spring...
    As current goes in, it pushes on the plate... the plate pushes current out the other side.
    The spring is going to resist this though, so you need a higher voltage to push the spring further against the spring. (If the voltage is too high, the part gets damaged of course)
    This is DC... the plate gets pushed and eventually stops when it moves far enough to be equal with the voltage pushing on it.

    This is the same in Parallel or Series connections... In series connections, this stops the DC because the plate can only move so far... When using AC, the plate gets pushed and pulled (which in turn, pushes and pulls current on the other side).
    When used in Parallel, it can help keep things running stable and smooth... a sort of shock absorber. When the voltage stops, the capacitor will begin to unload, and if the voltage spikes, the capacitor will absorb that.

    In reality, there are NO moving parts. There are two plates that are separated from each other. As the electrons pile on one plate, they push electrons off of the other plate. There is also a limit to the number of electrons you can fit on a plate, or how hard you can push them in. The affect is the same as a spring method, and if you have a hard time imagining how one electron can push another off a different plate. Go grab a couple magnets ;)
    Each electron has a charge which pushes against others of the same charge. An electron just has to be close enough to push another one... it does not have to touch.
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