DC Wave Questions

From: snipped-for-privacy@yahoo.com

2 questions about a fully DC Sine Wave....let's suppose you have a DC Sine wave which varies from +5V to +15V peak-to-peak going into a load with R, L, and C components..... Question #1: Is the load's impedance a function of R, L, and C (and wave frequency) or is it simply just R (i.e. Z=3DR)? In other words does non-resistive impedance (L + C) really only matter with an AC signal OR anytime voltage varies periodically (even if it is all DC)? Question #2: Would a "regular" negative peak detector ciruit, like shown here:
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work for the DC Wave described? Will it output +5V or do negative peak detectors only work for AC signals? Thank you.

~> This sounds like a Clamped Up Pulsating DC Waveform rather than a Sinewave.

In other words a true rms sinewave (as mentioned) equaling =3D [(-5 ~ 5)pp=

  • 10vdc clamper =3D 5 ~15 VDC] About the detector if you can set it's values, VCC to Gnd etc. (also mentioned) to detact the Less Positive
5VDC Value rather than a non-excistent negative value you're in business.

=AEoy

Reply to
Roy Q.T.
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Maybe you shouldn't believe everything you read. DC has:

  1. Constant amplitude (that's not to say you can't change it.
  2. Frequency of 0 Hz. Also, a non 0 frequency does not imply polarity changes.

Tam

Reply to
Tam/WB2TT

Not exactly useless, you just described a Zobel network.

It is used as crossover to feed two loudspeaker on HI range and LOW range presenting a constant resistive load to the Amp.

It is used to compensate a shunt at higher freq. The transfer function is perfectly flat even with two reactances in the circuit.

It is used to terminate a DC distribution line R+L with a R+C to avoid resonances, the line is perfectly damped, when the load current steps there are no oscillatory transients.

MG

MG

Reply to
MG

Again, is the term "DC Sine Wave" problematic because it is fundametnally wrong OR is it problematic because it is at odds with conventional terminology and nomenclature.....if it is fundamentally wrong, then please show how.....however, if we're just talking about convention, then why break balls? (Wait, I'm sorry, I don't mean literally "breaking balls", that's just nomenclature).....if you were given a piece of paper a week ago with just the words "A Fully DC Sine Wave" on it and you were asked to come up with as many possible things it could realistically mean, how many things could you come up with? If you were being truthful I think you could only think of one thing (and think of it very quickly).

Reply to
jackbruce9999

The signal would be said to have a DC-component (of the average value) and an AC-component(of the rms value minus the DC)

Reply to
Ban

Right...but your reply actually doesn't address the NET effect......if the wave had a DC-component of +2 V and an AC-component of 10Vpp, then the wave would be NET AC (since its polarity changes pos/neg/pos/etc.)......however if the DC-component was +10V instead, then the wave would be NET DC (since its polarity never changes polarity - i.e. always positive).....that is why I argue a "fully DC sine wave" is a BETTER (albeit unconventional) and more concise way to describe what I'm talking about (without using actual values) than the conventional description you provided....your description is ambiguos...could be NET "AC" (biphasic) or "DC" (monophasic)

Reply to
jackbruce9999

If the low peak of the sine wave (and the rest of the the sine wave for that matter) is "fully" above the "zero" reference point, then isn't it true that the current DOES NOT alternate? That is to say, that current only flows in one direction....i.e. "direct current"? Isn't it also true that if the low peak of the sine wave is -0.00001V then the sine wave results in current flowing in both direction (albeit for a nanosecond)....i.e. "alternating current".....I'm not arguing that my use of nomenclature is "pure" or conventional....but I don't see how it is fundamentally wrong, without merit, or lacking a reasonable basis.....

Reply to
jackbruce9999

Yes. DC by definition is zero frequency.

N
Reply to
NSM

The term "DC wave" is plain wrong, ask your teacher if you do not believe us. If you want to define new meanings for widely accepted definitions, it is ok, but do not try to communicate with anybody, because they will misunderstand you. Look at the definition of electric current flow. The convention is to say current flows from positive to negative, even if we know that the electrons move the opposite way. But because of the convention we keep up with the old definition to allow a communication with others. So you can make up a lot of logic constructs why you said this, it doesn't make it right. Your teacher will mark you a mistake and you will have to accept that. NO way out!

Reply to
Ban

Um, no. DC is Direct Current, i.e., current that flows in one direction. For example, the output from a rectifier is DC but it certainly isn't "zero frequency."

Reply to
Bob Penoyer

I concede my terminology is anti-convention, and "wrong" (with respect to convention) BUT I disagree with you here:

If you were given a sheet of paper a week ago, with only the phrase "a fully DC sine wave" on it, and you were asked to come up with as many realistic possible meanings, I have to believe that you could have only come up with one (and rather quickly)

If true, then your statement:

communication with others.

would hold true about "a fully DC sine wave" with respect to convention/"old definition" but not with respect to "communication" or ambiguity....while not "pure" or conventionally correct, is there really any other possible interpretation of "a fully DC sine wave" and therefore wouldn't you agree that being a "hyper-stickler" on this point is really not justifiable?

Again, isn't there more ambiguity (poorer communication) in your description:

AC-component

versus:

a "fully DC sine wave" versus "a partially DC-offset AC sine wave"

Reply to
jackbruce9999

Yes, your term "DC sine wave" is objectionable because it is fundamentally wrong.

I'm sure that one of your assumptions is that AC voltages flow through a capacitor. They do not. Now you go hit the books and discover how a varying voltage gets from one side of a capacitor to the other. Then you will be close to seeing your error.

Don

Reply to
Don Bowey

Here's one last tip to help you with the homework assignment I gave you earlier: You are wrong in assuming the current flows in only one direction.

Don

Reply to
Don Bowey

Let me try this:

would you object to

"a sine wave which (net) results in a current that only flows in one direction"

if you buy that, would you then accept it to be partially condensed into:

"a sine wave which (net) results in a non-polarity-alternating current"

if you buy that, would you then accept this:

"a sine wave which (net) results in a direct current"

and then

"a (net) direct current sine wave"

Reply to
jackbruce9999

You seem very attached to the word, "alternating" that is abbreviated in the term AC. Once people get involved in analyzing circuits and waveforms, they start to think in terms of frequencies. All kinds of signals can be described in terms of the frequencies they contain. Signals with zero frequency are analyzed and described as DC, while everything else is some frequency other than zero. And there are two distinct kinds of frequency. One is based on number of sinusoidal cycles in a given period of time and the other is based on exponential decay or growth rate (number of decay or growth time constants per time period).

I am sure that many who have not learned the math of Laplace transforms have a hard time thinking of a decaying, unidirectional pulse as a kind of frequency, since it never alternates, but there are such powerful analytical reasons to take this view that anyone who understands this power has little difficulty with this rather non literal extension of the AC frequency concept.

So only those with a very primitive view of frequency and are bothered by describing a non alternating but time varying signal as a kind of frequency (and informally called AC). The simple minded terms, AC and DC are just not up to the job of describing many waveforms, unless you are willing to be quite flexible in the usage.

Reply to
John Popelish

I will absolutely buy what you said, but understand the import of what you're saying....you're saying that the language of "AC" and "DC" has essentially been somewhat bastardized from its original meanings to also mean zero-frequency and non-zero-frequency signals. Therefore, to describe a 10Vpp signal with a 10VDC offset as an "AC" signal is actually contrary to the original connation of "alternating current" since it (net) results in a signal which yields only a mono-directional (i.e. direct) current flow (albeit time variant). So in a sense, you could say I am holding "pure" to the original (circa 1890's) definition of AC/DC while its use has been "officially" corrupted to cover the concepts of "zero frequency" and "non-zero-freuency".

Agree?

Reply to
jackbruce9999

What you describe is a 10V pk-pk sinewave sitting 'on top' of 10V DC.

The load current will depend on the RLC configuration. E.g. if there is series C then there will be no DC load current. Only the AC component will be affected by reactance either way.

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Graham

Reply to
Pooh Bear

Actually, you haven't provided anything useful along the lines of "tips" and you avoided responding to a previous reply of mine....but anyway, what you say is interesting:

O.K., then please let me know how current would not flow in only one direction in the following example:

Reply to
jackbruce9999

Yes !

Graham

Reply to
Pooh Bear

Nice parse-job.....here's my original entire comment in context:

You conveinently left out the "OR...." part. You actually proved my point that DC is DEFINED (i.e. by convention) as "zero frequency". Is it that weird to posit that the superior concept with respect to considering any signal as AC or DC, be the actual NET current flow? I could see your point if signals were classified as either "ZF" ("zero frequency") or "NZF" (non-zero frequency") but we are dealing with "DC" or "AC"

Reply to
jackbruce9999

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