# Capacitor charging circuit

#### wgs

May 3, 2012
4
In a simple series R/C circuit connected across a power supply, the cap will charge exponentially. How can I make a simple circuit to charge and discharge the cap linearly?
Thanks,
Walt

p.s. - I made a sketch of this circuit and saved it as a .gif file, 750kb (less than 1 meg). I could not attach it because it is too large. What is the max attachment size?

#### davenn

Moderator
Sep 5, 2009
14,085
p.s. - I made a sketch of this circuit and saved it as a .gif file, 750kb (less than 1 meg). I could not attach it because it is too large. What is the max attachment size?

There's no need for huge files
make the image smaller (resize it .... best way is to use a .jpg type file and make sure it isnt bigger than ~ 800x600 pixels
then save it at ~ 60% quality

#### Bluejets

Oct 5, 2014
5,995
How can I make a simple circuit to charge and discharge the cap linearly?
Constant current....

#### wgs

May 3, 2012
4
Constant current....
O.K., I get that - can you elaborate? Maybe point me to a sample circuit somewhere that would work.

Thanks,
Walt

Here's the file I originally wanted to attach.

Last edited:

#### ramussons

Jun 10, 2014
448
There are many ways to charge a capacitor linearly.
* Use an OpAmp integrator.
* Use a Transistor as a Constant Current source.
* Use a Very High voltage to charge the capacitor through a Resistor.
*
It all depends on the Voltage Range, Capacitance, and the Linearity required.

#### roughshawd

Jul 13, 2020
255
I think jets is right...
I had once theorized I could fire a solenoid with a cap discharge but it didn't work because everything just dumped to ground... since then I have thought of a capacitor as a solenoid, and it's been working fairly well!!! After thinking about it, put a battery in there and it should work... what you are describing is a battery for all intents a purposes.

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