# Quick question: Capacitor and a switch

Discussion in 'General Electronics Chat' started by toughspeaker, Aug 28, 2009.

1. ### toughspeaker Thread Starter Active Member

Jan 28, 2009
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Hi guys, what is the exact reason why one puts a capacitor in connection with a switch when designing a circuit? Ive read somewhere that the capacitor will be reducing ripple when pushing the button? Is that correct? Or to smooth out the current?

2. ### t06afre AAC Fanatic!

May 11, 2009
5,939
1,222
In general a battery do not have any ripple. You will get ripple then you convert an AC voltage to a DC voltage. It could be number of reason why the capacitor is placed in the circuit diagram. It could be as you mention smoothing. But also filtering if the battery is connected to circuit by long wires. Also many voltage regulator circuits does require a capacitor on the input for stability. It would be helpful if you can provide some info about the capacitor size and the load.

3. ### BillB3857 Senior Member

Feb 28, 2009
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Doesn't the cap provide a level of "debounce" to the switch?

4. ### russ_hensel Distinguished Member

Jan 11, 2009
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In an ideal cap. switch, and battery there would be a brief infinite current. In a real case too large a battery and/or cap might fry the switch.

Jan 28, 2009
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6. ### rspuzio Active Member

Jan 19, 2009
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First, you need to take into account the resistance. Somewhere in the circuit,
there should be a resistance which limits the current which can flow into the
capacitor (this need not be an explicit resistor; it might, for instance, be
provided by the internal resistance of your battery). The time it takes for the
capacitor to fill up is given by RC; you want to arrange for this to be a few
milliseconds because the bounces of a switch happen within a time scale of
5 ms or thereabouts depending on your particular switch.

7. ### toughspeaker Thread Starter Active Member

Jan 28, 2009
40
0
Fabtastic Rspuzio, thank you very much for your answer, it helped ALOT!