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Just a forewarning I am a complete rookie when it comes to capacitors

I am looking to supply a 0.5mV charge into a capacitor, then have the capacitor discharge to a battery once the accumulated charge reaches 4V. Once the stored charge on the capacitor is below 4V, the capacitor should store the energy again until the accumulated charge reaches 4V to repeat the cycle listed above.

So basically I am looking to have a low voltage input into a capacitor, and have the capacitor discharge to a battery only when the stored charge is above 4V. What type of circuit is capable of this task? Will just a super capacitor work?

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  • \$\begingroup\$ It doesn't make sense that you are supplying 0.5 mV into a capacitor and expecting the voltage to accumulate. Might you supplying a CURRENT of 0.5 something into the capacitor rather than a voltage? In other words, what is your source of power? \$\endgroup\$ – Dwayne Reid Mar 24 '15 at 21:50
  • \$\begingroup\$ Assume my source of power comes from a generator which outputs a very low current such as 20mA or a power output of 1mW \$\endgroup\$ – Jeff K Mar 24 '15 at 22:02
  • \$\begingroup\$ 0.5 mV is a voltage, not a charge. If you connect 0.5 mV to a capacitor, it will then have 0.5 mV across it, which is never 4 V. How are you "accumulating" these voltages? \$\endgroup\$ – Greg d'Eon Mar 24 '15 at 22:46
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you can never charge that capacitor above 0.5mv.When you connect a voltage source across the capacitor current will flow from source to the capacitor until the capacitor voltage equals the source voltage. So if you want to charge the capacitor to 4v you have to supply 4v at its terminals.

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If you want to power your capacitor from a low voltage source and then charge it at 4 volts you will need to increase the voltage.Something like a powerful DC to DC step up converter or a step up voltage regulator or a step up transformer.Then you will need something to sense the voltage across the capacitor.A microcontroller can do that with high accuracy,like Arduino and Raspberry Pi.There should be integrated circuits that can do it as well.

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