Is it a rule? Large cap before small cap?

[superflux]

Before feeding a voltage regulator, is power required to go through the larger size cap before the smaller cap - if 2 caps are being used?

SF

 

[bychon]

Current doesn't go through caps. It piles up and waits to be released.

I think you mean, does it matter which capacitor is first when two of them are in parallel to each other. No. As long as they are right next to each other and the regulator chip, it doesn't matter. Several inches of distance does matter. Make 'em snuggle up together.

 

[MikeMl]

If capacitors are connected in parallel, then there is no first or second. When bypassing (shunting) an unwanted AC component at any node, sometimes a small value ceramic capacitor (1nF or 10nF) is connected in parallel with a large electrolytic capacitor (1uF to thousands of uF) because the small one is good at bypassing AC frequencies from hundreds of KHz to MHz, while the large one is good for audio to 50 Hz...

 

[superflux]

I think you mean, does it matter which capacitor is first when two of them are in parallel to each other.

That's exactly what I mean. I think all I've seen on schematics lately have the larger one first and I thought I might be missing something.

I'm sure I'm not the only one who was wondering...

Thanks guys!

 

[Brevor]

YES !
In my experience the smaller cap is always closer to the regulator because you want it as close to the pins as possible. A large electrolytic just can't get that close.

 

[Mikebits]

YES !
In my experience the smaller cap is always closer to the regulator because you want it as close to the pins as possible. A large electrolytic just can't get that close.

I see what your thinking here, but we are not talking RF frequencies are we? Whats a centimeter or two amongst friends, ie. At kilohertz I doubt it matters. Granted bypass caps should be placed close as possible and it does make sense that the smaller cap first would create a shorter path.

 

[Hero999]

Put the larger capacitor near the regulator and the smaller one as near to the device you're powering as possible.

 

[Vizier87]

I'd go with Sir Hero's, I've seen 4 of my PIC main boards go awry due to placement of capacitors... due to not placing caps at all sometimes.

 

[Ubergeek63]

I see what your thinking here, but we are not talking RF frequencies are we? Whats a centimeter or two amongst friends, ie. At kilohertz I doubt it matters. Granted bypass caps should be placed close as possible and it does make sense that the smaller cap first would create a shorter path.

actually you are talking RF ... if you look at linear reg specs... well back in the day they bothered putting the info on them at least... they were only good for audio and some broke into oscillation when the were not properly bypassed.

you still see it on some of the older low drop outs...

dan

 

[crutschow]

Some old linear regulators actually depended upon the ESR of an electrolytic capacitor for stability. If there output was bypassed with a low ESR ceramic they could oscillate.

 

[Ubergeek63]

Some old linear regulators actually depended upon the ESR of an electrolytic capacitor for stability. If there output was bypassed with a low ESR ceramic they could oscillate.

on the output yes...