Axe401 Caps

marzan

Senior Member
Hello. Can anyone tell me if caps C1,C2,and C3 have to be 35V ? It`s just that I have heaps of 16v ones if they are suitable.

Thanks.
Marz.
 

BeanieBots

Moderator
Hello. Can anyone tell me if caps C1,C2,and C3 have to be 35V ? It`s just that I have heaps of 16v ones if they are suitable.

Thanks.
Marz.
That would depend on what voltage to run it from.
The general rule is that your caps should have a voltage rating of about twice the voltage across them.
C2 will see whatever your input voltage is. If you are using a 9v input then I would suggest you keep it at 35v.
C1 and C3 are on the regulator outputs so these could be 16v if you want.
For switchmode power supplies you will often find 35v (or higher) rating caps on 5v lines. This is because higher voltage caps offer higher ripple current ratings and has nothing to do with the actual voltage rating. Though some types of cap need to be run close to their rating to keep the electrolyte happy. (read the cap datasheet if in doubt).
 

Jeremy Harris

Senior Member
16V is fine for C1 and C3 and may be OK for C2 if you can always guarantee that the input voltage to the 5V regulator will be less than 16V. Capacitor derating, even for defence high reliability requirements, usually means a derating factor of around 30 to 50% on the voltage rating, although it's temperature dependent to some degree. For hobby purposes going to within 10% of the max rating is usually absolutely OK.

[Edited to add that this reply crossed with the one above - we must have been typing together!]
 
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