Is there any rule of thumb for over-designing the output capacitor of a DC-DC converter (say for example a buck converter)? I mean, when we calculate a minimum capacitance value for Cout (based on output voltage ripple and ESR), how larger the capacitor is typically selected? Say for example, we have calculated a minimum of 1uF, now what is typically selected ? Is it 2 times higher, 3 times higher, or what?
Thanks!
There is 2 types of distortion in DC output voltage. first: a voltage ripple that depend on output capacitor and switching frequency. second: spike voltage on DC output voltage which depend on your capacitor type, capacitor quality and even PCB design.
if you use larger capacitor you decrease voltage ripple but maybe increase spike voltage.
ESR and ESL of capacitor create big voltage spike Compared with voltage ripple.
So if you calculate a value for output caps you don't need to over-design it but instead you can add some small capacitor in parallel to reduce voltage spike. or even use a tiny LC filter in output stage. and remember DON'T USE ONE BIG CAPACITOR, USE SMALLER CAPACITOR IN PARALLEL.
Generally, we calculate the capacitance value based on the frequency, load type, and voltage stress across it. Usually, we take the capacitance value 1.5 to 2 times of the calculated value.
the capacitor must natch your voltage o/p and be careful better filtering Capacitors cause high current (power) absorption.
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