Voltage Regulator De-coupling (Capacitor Voltages)

[David]

Hi all,
Just a quick question on de-coupling linear voltage regulators. How important is the voltage rating of the capacitor? I know it is good to "de-rate" the capacitor (e.g. use a 10V for 5V supply) but if you have say a 1.25V supply would using a 16V rated capacitor make any difference at all?

Dave

[septer012]

I believe just from watching the video Dave did on capacitors, at least in electrolytics its the amount of pressure/strain the capacitor can be under before failing.  So I dont think a 100V capacitor would make any difference in a 5v application vs a 15v capacitor.

[EEVblog]

For most applications the voltage rating is of little importance once you do the usual de-rating
If you want to go into ultra high reliability engineering (for something critical that must work for decades for example) then it's a different matter and would require thorough investigation. But that's a whole different ball game.

Dave.

[GeekGirl]

Hi all,
Just a quick question on de-coupling linear voltage regulators. How important is the voltage rating of the capacitor? I know it is good to "de-rate" the capacitor (e.g. use a 10V for 5V supply) but if you have say a 1.25V supply would using a 16V rated capacitor make any difference at all?

Dave

Depends on if you are doing it for a one off or a mass produced product, one off, price does not matter, mass produced, every 1/2c matters, higher voltage rating is more expensive. I usually double the expected to voltage (to a point, (if I am expecting 340V then I might use a 450V)) ie if I need a 5V then I will choose a 10 or 16V.
 

[Zero999]

I've found high temperature to be more damaging to electrolytic capacitors than voltage.

Using 105°C capacitors rather than 85°C capacitors is probably better reliability wise than higher voltage.

It depends on where the capacitor is and the power supply. If it's on the output of a linear regulator then there seems little point in de-rating it unless the output voltage is really close to the rated voltage. If its on the input to a linear regulator where the supply voltage can be unstable then it makes more sense to use a higher voltage.

If the capacitor is across the output of a 5V supply then 6.3V is probably fine but if it's a 6V supply then go for 10V.

[David]

Thanks for the replies guys. It seems my suspicions were correct 

[Simon]

as said by other people going mad won't help 2 X is a good idea if uncertain but if your after extra hardiness goes for higher temp rated caps.

[Zero999]

I've thought of another thing that can shorten the life of a capacitor: ripple current, the AC current flowing through the capacitor. If a capacitor is used to decouple a speaker or is placed across the rectifier of a DC supply the ripple current can be considerable which will cause heating and distruction of the capacitor if it's too high. In this case, chose a capacitor with sufficient ripple current rating and the lowest ESR and ESL specifications you can afford.

[Simon]

if you suspect high ripple current use as many capacitors in paralel as you can, typically 2-5