What's the deal with the V of PSU bypass caps??

[Freq Band]

I built a standard 78xx pos/neg PSU and for the 100n caps, was told 250volts was OK.
...so why have a voltage rating on these at all? Why aren't they all just a "Super Filter Cap 1kv :razz: " ?

..or was I fed bad advice?

=FB=

 

[alk509]

Size?

Peace,
Al.

 

[Freq Band]

size matters? :shock:

was that an answer, or another question?

 

[Greg]

I think what alk is trying to say is that as the voltage rating goes up, the size goes up. Take a look at a 47u25V cap and a 47u350V cap. Big difference in size. Same is true for non-polarized. A 100n250V vs 100n1kV would have a big difference in size.

 

[Svart]

rule of thumb is find your output voltage then find a voltage of a cap that is the closest to the rail voltage but still over, then go t the next voltage rating up.

example:

15v regulator output -> 16v cap -> choose 25v cap.

easy.

it's often cheaper to buy a bag of caps rated for the highest voltage you will use and just use them.

coupling caps usually aren't more than 6.3v or so but psu caps are often 25-35v. buying a bag of 25v caps for them all is usually cheaper. beware of the size of the cap though as Greg mentioned.

 

[Freq Band]

Oh, that size.
So if I wanted to, I could use 600v caps in a 5v psu...if I had the room....and those caps looked "neato" ? ?

How does this apply to the filter/smoothing lytic caps? Is this just a size thang too??

=FB=

EDIT" posted late......Svart...what is the actual reason not to go overboard on the voltage?

 

[Svart]

yes same thing.


cost is your obvious motivation for trying not to overkill in this situation.

:thumb: