save voltage

[Fahime]

I have a small circuit. I want it treat as follows: When I press the key, I need my circuit saves voltage via charging a capacitor and by releasing the key the circuit starts to work. But I don't know the fondamentals. What factors should I consider?

 

[Optikon]

You should consider differential equations and modelling real world capacitors.

 

[Fahime]

more

You should consider differential equations and modelling real world capacitors.

could u please explain more?

 

[Hero999]

What do you want to power?

Read the Wikipedia artical and understand all the equations.

https://en.wikipedia.org/wiki/Capacitor

 

[Papabravo]

A differential equation is one that involves a function and it's derivatives. It is often used in systems where something we are interested in is changing and the rate at which it is changing changes. To keep track of all these things which are changing we write relationships involving a function and it's derivatives.

There are two main classifications: ordinary and partial. In an ordinary differential equation we have a single independent variable. In partial differential equations there can be many independent variables.

There are general purpose solution techniques for many types of ordinary and some partial differential equations.

Real capacitors have a frequency dependent impedance characteristic. At DC they represent an infinite impedance until the voltage rises so high that the material between the "plates", the dielectric, breaks down and a spark reduces the voltage. As the frequency goes higher and higher the impedance heads for zero. When the wavelength becomes significant with respect to the dimensions of the part all sorts of unusual things happen.

 

[Hero999]

Also, beyond a certain frequency a capacitor will become an inductor.

 

[Dr.EM]

Are you after a sample-hold circuit?

 

[Papabravo]

Also, beyond a certain frequency a capacitor will become an inductor.

Or even a resonant cavity with the edges at zero potential as if there was a wall connecting them. That was just about my favorite Feynman lecture

 

[audioguru]

Do you want to charge the capacitor then use the charge to power a circuit for a short time?
A discharging capacitor's voltage starts dropping immediately it has a load and the voltage drops sharply. The time constant of the value of the capacitor and the resistance of the load is easily calculated for the time it takes for the voltage to drop to any percentage of the full charge voltage.
Maybe your load draws too much current to be powered for longer than a few milli-seconds from a huge capacitor.
Maybe your load won't work properly from a supply voltage that keeps dropping.

 

[Fahime]

...

Are you after a sample-hold circuit?

I want to charge the capacitor then use the charge to power a circuit for a short time. Actualy the point is that I like my circuit starts to working after releasing the switch, not while pressing it.

 

[eblc1388]

A simple SPDT push button is what you'll need.

The common "C" of the push button is connected to the capacitor positive terminal. The "NO" to battery and "NC" connected to load.

When you push the switch, the capacitor gets charge and when you release it, your load get the charge from the capacitor.