There are times when you may need to rate a capacitor for AC voltage. An example would be a capacitor used for noise suppression across the AC mains wall power input of an amplifier. Usually a capacitor is rated for maximum DC voltage. The AC rating of a capacitor is about one third the DC rating.
You can use the DC rating of a capacitor to determine its AC rating using the following formula.
ACV RMS= Vpp / (2 X √2)
(Vpp = CAPACITOR DC RATING)
For example, a capacitor with a 600VDC rating.
ACV RMS = Vpp / (2 X √2) =
600 / (2 X √2) =
600 / (2 X 1.414) =
600 / 2.828 = 212VAC
For bypassing AC circuits ceramic capacitors are a good choice.
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