Definition of AC vs DC power

If I have an AC power supply alternating between -1V and +1V and I add to it (in series) a DC supply of 10V, is the resulting power supply (which varies between 9V and 11V) an AC supply or a DC supply?

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** DC.

Cos the voltage never changes sign.

..... Phil

Reply to
Phil Allison

Both. It has AC and DC components.

But the terms AC and DC aren't absolute, so don't take them too seriously.


Reply to
John Larkin

What you call it depends on what you want to do with it.

It's a crappy DC supply, or a _really_ crappy AC supply, or a DC supply with an impressed AC component, or, or, or.

Reply to
Tim Wescott

Why do you want a definition?

The reason for that need may help to define the answer.

The concept is hardly out of the ordinary. Lots of circuits over the years have that very situation, a tube or transistor fed from a DC voltage, but amplifying an AC voltage. Nobody fussed over the definition, it was a natural thing (since the circuit needed the DC), and you ignored whatever one that wasn't the issue at the time. Coupling capacitors would strip off the DC component when only the AC was wanted (such as when feeding the output of one stage into the other, and each stage was biased separately so you didn't want the DC voltage from the output of one stage to get into the input of the next stage) or a big coupling capacitor at the output of an audio amplifier to keep the DC off the speaker.

Perhaps the concept is less common now since a lot of equipment does run off dual-polarity power supplies.


Reply to
Michael Black

It's effectively a DC supply, as the current no longer "alternates" in direction. More commonly it might be clarified as a "DC supply with AC ripple" or some such. But what you call it depends on how you want to interpret it for your application/need. e.g. It may not be incorrect to say it's an "AC supply with a DC bias" There are no absolute definitions here.


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Reply to
David L. Jones

Corranet Inscribed thus:

Its a DC power supply with 20% AC ripple.

Best Regards:
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A DC supply with a ripple on it.

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Or an AC supply with an offset, or bias, of +10V. ;-)

It depends on the application.

Hope This Helps! Rich

Reply to
Rich Grise

Yup; a +10 volt DC supply with a one volt (Peak) ripple on it.

Or you could consider it a 0.71 volt (RMS) AC supply biased by +10 volts DC.Making an assumption here that the one volt variation is some sort of typical sine wave. If it is not a typical sine wave variation (it could be a chopped or square wave variation).

Sounds like a school question to get someone to think about voltages; not look for a strict black/white definition!

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