Voltage Regulator De-coupling (Capacitor Voltages) - Page 1
Forum section: electronics / general

author: David
author_rank: Frequent Contributor
timestamp: December 27, 2009, 11:46:38 pm
content: 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

author: septer012
author_rank: Regular Contributor
timestamp: December 28, 2009, 09:44:49 am
content: 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.

author: EEVblog
author_rank: Unknown
timestamp: December 28, 2009, 10:43:03 am
content: For most applications the voltage rating is of little importance once you do the usual de-ratingIf 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.

author: Unknown
author_rank: Unknown
timestamp: December 28, 2009, 11:28:36 am
content: Quote from: David on December 27, 2009, 11:46:38 pmDepends 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.

author: Zero999
author_rank: Super Contributor
timestamp: December 28, 2009, 11:42:22 am
content: 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.

author: David
author_rank: Frequent Contributor
timestamp: December 28, 2009, 06:45:00 pm
content: Thanks for the replies guys. It seems my suspicions were correct

author: Simon
author_rank: Unknown
timestamp: December 28, 2009, 09:07:41 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2009, 01:18:01 pm
content: 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.

author: Simon
author_rank: Unknown
timestamp: December 29, 2009, 01:37:27 pm
content: if you suspect high ripple current use as many capacitors in paralel as you can, typically 2-5