On Tue, 12 Oct 2004 17:10:41 -0500, "Steve Nosko"
wrote:

This could be viewed as what we call a "clamper circuit" The AC voltage
AT THE BASE will have its positive peak "clamped" or moved to +0.7 volts and
the waveform will extend from there as negative as the waveform is tall.

IF we had 5 volts peak (10 volts peak-to-peak) the cap left side, the base
voltage will swing from +0.7 volts to -9.3 volts.

Okay, upon further thought about this there's still something amiss in
my understanding. I take what you say about the cap blocking out the
DC component of the waveform to leave the AC largely unaffected.
However, the term "clamping" AIUI means the diode lops off anything
over about 0.7 volts from the input waveform (ie, it conducts it away
to ground) so around half of it is lost (half wave rectification). Now
you state (and the spice progs agree) that what *actually* happens in
this case is that the whole AC waveform gets shifted south into
negative territory. It's still a full wave, but it's way down into
the negative and only the highest peaks just creep above zero volts.
Is this effect *solely* attributable to the steady build-up of
negative charge on the cap's RHS? I think what's really freaking me
out here is the fact that the signal source is grounded on the neg.
side and yet we have that same signal that after going through a cap
can end up going fully negative *below* ground. It just seems like any
such voltage beneath zero/ground potential is breaking the laws of
physics. Ground should be the 'absolute zero' of the potentials in any
circuit and here it is being violated. I need some help to get my
thick head around the concept! :-(
--

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