Electronics Forums > Re: DC Wave Questions

# Re: DC Wave Questions

Bob Monsen
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Posts: n/a

 06-11-2005, 12:10 AM
(E-Mail Removed) wrote:
> 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=R)? 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)?
>

The impedance of a set of passive devices is independent of the voltage
across them. It only depends on R, L, C, and f. The fact that there is a
DC component makes no difference.

An inductor will pass DC current as if it were a wire. Only differences
in current cause a voltage across it. A capacitor will not pass DC, so
the DC does not matter. Obviously, a resistor is a resistor, and cares
nothing for ac vs dc.

This is only true for ideal components. In the real world, inductors,
caps and resistors have voltage limitatations. They are usually well
beyond 15V, though.

>
> Question #2:
> Would a "regular" negative peak detector ciruit, like shown here:
>
> http://www.elektroda.net/cir/index/D...CTOR.htmgative
>
>
> work for the DC Wave described? Will it output +5V or do negative peak
> detectors only work for AC signals?
>
> Thank you.
>

Your link has crap on the end. Here it is without the crap:

http://www.elektroda.net/cir/index/D...20DETECTOR.htm

With this circuit, the input at V+ will always be outside the power
rails. Thus, it will not work.

NOTE: I changed the followup-to field to sci.electronics.basics, because
that is where this thread belongs. I hope you don't mind.

---
Regards,
Bob Monsen

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