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

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