Capacitor voltage rating - AC or DC

The capacitor does not know what peak to peak means, all it notices is *peak* voltage across its terminals at any time.

And if non polar (which is the case), it does not care about polarity either.

As of:
there is peak to peak AC of 130V, which means the RMS is 46V.
that blanket statement is wrong, unless you qualify it with "the signal present is a perfect sinewave"
 
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HiFiNutNut said:
So for use in 135 peak to peak AC voltage only, is the 100VDC rated capacitor good enough?
It depends on what you mean by peak to peak. If you really mean peak to peak, with no DC present and a quiescent voltage near the middle, then 100V rating is enough for 67.5V peak. If you actually mean that the voltage can vary from +5V to +140V (which is also 135V pk-pk) then no. As always, context is everything.
 
Thank you very much. I now understand it.

The 100V capacitor is underrated then because there can be 112V across it based on the current rail voltages of 56VDC.

I have been playing the amp for a couple of months now and so far I have had luck. Possibly the MLCC SMD can stand 12V more voltage or perhaps I never played music to push the output higher enough to put over 100V across the cap.
 
The 100V capacitor is underrated then because there can be 112V across it based on the current rail voltages of 56VDC.
Not necessarily.

You don't tell us where to where is the cap connected.:confused:

as in:

* if cap is connected from speaker out to ground (as in Zobel cap) then it can see 56V peak maximum ... period ... no big deal.

* if cap is connected from one rail to speaker out, then yes,on opposite polarity peaks it can see up to 112V peaks.

* you don't mention this,but just for the full picture: if cap is bypassing rails to ground, then it sees 56V DC

* or if it is across power transformer secondary winding, end to end , quite common to minimize dirty line interference, it will see 112V peaks

in fact, you should have stated its connection or shown a schematic ;)
 
You don't tell us where to where is the cap connected.:confused:

It is used between drain and gate of the output LMOSFTs, as mentioned in the third line of my original post. :)

So there can be maximum 112V across the cap. I have now replaced it with a 400V silver mica :)

Thanks again. I now understand it after you shed lights. :)
 
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