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Old June 22nd 05, 05:25 PM
ehsjr
 
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Kevin Aylward wrote:
ehsjr wrote:

Kevin Aylward wrote:



All this misses the point, which was the analysis of
an R,L,C load impedance in the presence of both a DC voltage
and an AC signal. The answer given seemed to indicate that
you analyze the circuit for AC and for DC separately.



One does. However, this doesn't meant that one completely ignores DC
conditions on component parameter values.

The issue here is one of the context of the claim.


If you don't consider saturation, your analysis could be wrong.
Neither the AC signal by itself, nor the DC voltage by itself,
might cause a current at or over the saturation point, if
there is one. But combined, the possibility exists that
saturation might occur. The DC voltage alone might cause
a current at or over Isat, while the AC signal might result in
currents below Isat. The point being that when analyzing
the circuit in the presence of an AC signal, you must
at the same time consider the DC voltage. Separate analysis
could result in the wrong answer.



But, this is out of context. When someone says that they are analysing
AC and DC separately, they don't *really* mean that they are completely
oblivious and are ignoring the fact that, e.g. an inductor might
saturate if it has a DC current through it. They simple mean that, for
the ac analysis the dc level is not relevant and take it as already read
that such analyses is performed with the *correct* value of inductance
for the inductor.


Kevin,

I'm glad you know what people *really* mean. :-) However, you
*really* do need to read the relevant posts again.
Here's the context:

Er - there are cases where the L will be saturated by
the DC component.


What you are suggesting is a good issue to keep in mind for the real
world (and one I had overlooked).


Saturation was overlooked. Case closed.

snip



Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.



  #363   Report Post  
Old June 22nd 05, 05:51 PM
Kevin Aylward
 
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ehsjr wrote:
Kevin Aylward wrote:
ehsjr wrote:

Kevin Aylward wrote:



All this misses the point, which was the analysis of
an R,L,C load impedance in the presence of both a DC voltage
and an AC signal. The answer given seemed to indicate that
you analyze the circuit for AC and for DC separately.



One does. However, this doesn't meant that one completely ignores DC
conditions on component parameter values.

The issue here is one of the context of the claim.


If you don't consider saturation, your analysis could be wrong.
Neither the AC signal by itself, nor the DC voltage by itself,
might cause a current at or over the saturation point, if
there is one. But combined, the possibility exists that
saturation might occur. The DC voltage alone might cause
a current at or over Isat, while the AC signal might result in
currents below Isat. The point being that when analyzing
the circuit in the presence of an AC signal, you must
at the same time consider the DC voltage. Separate analysis
could result in the wrong answer.



But, this is out of context. When someone says that they are
analysing AC and DC separately, they don't *really* mean that they
are completely oblivious and are ignoring the fact that, e.g. an
inductor might saturate if it has a DC current through it. They
simple mean that, for the ac analysis the dc level is not relevant
and take it as already read that such analyses is performed with the
*correct* value of inductance for the inductor.


Kevin,

I'm glad you know what people *really* mean. :-) However, you
*really* do need to read the relevant posts again.
Here's the context:

Er - there are cases where the L will be saturated by
the DC component.


What you are suggesting is a good issue to keep in mind for the real
world (and one I had overlooked).


Saturation was overlooked. Case closed.



Well, I suppose I will have to qualify that with "those that really know
what they are doing"

Its so obvious to pros that inductors might well saturate, that they
simply wont address that issue when responding to basic electrical
questions on AC and DC analysis. You can't qualify everything one says.
One has to assume something to avoid reams of verbiage.

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.


  #364   Report Post  
Old September 29th 05, 10:02 AM
Tom Grayson
 
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Hey JackBruce
I got fed up with the crap the other posters wrote about your terminology,
and did not really see if anyone actually answered your question, Which, by
the way, Was very easy to understand. Ignore the other jackasses here, that
nitpick. They have too much time on their hands, i can see.

Question 1
The impedance of inductors and reactors is based on the varying signal
frequency, Weather it is offset by the DC component or not.
This answer assumes that you are not reaching the current limit of any of
the devices, naturally if the DC Current in the "L" Device saturates the
Flux medium ( air or iron) then you will get non linearities introduced,
Not sure what the limit on a "C" Device would be, probably current again.

Question 2
The link didn't work but most of the modern devices looking for peaks and
valleys work fine with a DC Offset.

Tom Grayson

wrote in message
ups.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=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)?


Question #2:
Would a "regular" negative peak detector ciruit, like shown he


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.



  #365   Report Post  
Old October 5th 05, 11:34 PM
Danny
 
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I've just noticed this 'long' thread. It is of interest to me as I had
a not dissimilar problem. The use of superposition is absolutely
correct in a linear system where the system component values do not
vary with the signal applies. However, when applying the ac component
the skin effect phenomenon will deplete the current carrying carriers
from the centre of the conductive component thus reducing the effective
cross sectional area......which will also effect the dc
resistance....or will it?

Danny



  #366   Report Post  
Old October 5th 05, 11:57 PM
Reg Edwards
 
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"Danny" wrote in message
ps.com...
I've just noticed this 'long' thread. It is of interest to me as I

had
a not dissimilar problem. The use of superposition is absolutely
correct in a linear system where the system component values do not
vary with the signal applies. However, when applying the ac

component
the skin effect phenomenon will deplete the current carrying

carriers
from the centre of the conductive component thus reducing the

effective
cross sectional area......which will also effect the dc
resistance....or will it?

Danny


========================================

No, it won't. However, it does appear have affected superposition of
your thinking processes. ;o)
----
Reg.


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