# 3.6V battery filtering Capacitor calculation

I am using the follow battery as power supply:

http://uk.farnell.com/eve/er26500/battery-lithium-3-6v-c/dp/1973582

The circuit demands a constant current of 0.01 mA until an interrupt happens where the current demand varies from 18mA up to 90mA for 4 seconds.

I have read that "In power supplies, capacitors are used to smooth (filter) the pulsating DC output after rectification so that a nearly constant DC voltage is supplied to the load".

Is it correct to say that filtering capacitors on power supply is similar to decoupling capacitors? As i can understand both techniques has the same benefits, right?

I am sure there is a way to calculate the capacitor value exactly, but is there any common values for 3.6 volt batteries on these current demands? (like decoupling capacitors).

For an example i have device that uses the same battery as i do, and they used two parallel capacitors 1F each. Moreover, i can make a guess that the current consumption will be increased if i use capacitors after the power supply.

Is there any other disadvantages on using them?

• What makes you think you need to add capacitance? Can you be specific about the "pulsating DC output" that you see? – Elliot Alderson Jul 4 '18 at 12:19
• If there were no parasitics,in an ideal world, this voltage drop in case of current demand increase does not happen. Batteries are pretty close to ideal, given that you can tolerate a range of voltages. If you can distribute your power in low impedance, a battery will supply a steady voltage. 1F is a supercap and is used for an other purpose. – mehmet.ali.anil Jul 4 '18 at 12:41
• I am not sure if i need additional capacitance. Actually, i don't have a clue. I was reading about capacitors on power supply and then a saw a similar design which was using them, so i thought maybe i should add them too. I didn't observe a pulsation DC output but i was wondering if the current demands in those two seconds may cause a functionality problem. I don't observe any but i am not sure what can happen on a long period. That's why i posted the question. – alexisicte Jul 4 '18 at 12:48