Electronics > Electronics

capacitor discharge

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waltr:
The formulas can easily be obtained by using Google and Wikipedia.

Also, If discharging a cap with a constant resistance the current is NOT Constant but decreases exponentially. That's what the equation jkerns posted tells you.

sherby:
I would like to get some information about selecting capacitor too!
Is there a post or some information, to get help in selecting proper capacitors with proper values?

Thanks in advance!

jwatte:
That kind of depends what your intended use is!

If you need a particular time constant at a particular resistive load, then you can calculate the capacitance needed from that.
If you need a particular ripple current tolerance, then that's typically listed for the capacitors, and is searchable in most parametric search tools. You can also calculate it from the power and ESR, given the above formula.
If you have a particular voltage you need to use, make sure the rating is higher than the voltage by a safe margin (50% is a good margin.)

I like the digikey.com parametric search tool:
http://www.digikey.com/product-search/en/capacitors/aluminum-capacitors/131081

Note that if you need very low ESR, or very small form factor, or some other extreme parameters, you may want to look at chemistries other than aluminum. (Tantalum, ceramic, PTFE or mylar film, etc.) Those are also searchable on digikey, if you navigate through their parts index.

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