Electronic – Deciding capacitor value to use in the circuit

capacitordecoupling-capacitorpower supplyswitch-mode-power-supply

I have a power source which supplies 1A at 5V. I am using a switching regulator which supplies 1.3A at 3.3V. The load requires a burst of 2A without reducing the voltage across it than 3.2 V for 477 usec after every 5 minutes. The normal operating point is 500 mA at 3.3 V.
I want to use a capacitor to provide that extra current for the required duration without reducing the voltage.
How to choose proper capacitor value with low ESR?

Best Answer

You start with $$ Q = CV $$ and differentiate both sides, $$ \dfrac{dQ}{dt}= C\dfrac{dV}{dt} $$, which can be represented by $$ I = C \dfrac{dV}{dt}$$, rearranging variables you get $$ \dfrac{I}{\frac{\Delta{V}}{\Delta{t}}} = C $$

Using your values from above, $$ \dfrac{2 [A]}{\frac{(3.3 - 3.2)[V]}{477 [us]}} = 9.54 [mF] $$