Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
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RLC circuit - RF Cafe Forums
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
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Forums activity dropped off precipitously. If the folks at
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sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
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Post subject: RLC circuit
Unread postPosted: Wed Mar
16, 2005 8:30 am
Ok, I am having a problem with a RLC circuit
and my teacher was unable to offer a satisfactory explanation. Hope
that you'll help.
Consider a DC battery, a switch, a resistor, a
capacitor and an inductor in series. Before t=0 the switch is open and
assume that the circuit has achieved steady state. This means that the
capacitor voltage is 0 and so is the inductor current. At t=0 the switch
is closed. It follows that at t=0+ (i.e. just after t=0) the capacitor
voltage will be 0 and so will the inductor current. It also follows
that the voltage across the inductor at t=0+ will be V, i.e. the voltage
of the source (the capacitor is acting as short-circuit and the inductor
as open circuit). Therefore the rate of change of current in the circuit
at t=0+ will be some positive value (from v=L di/dt). But the rate at
which the capacitor voltage is increasing is ZERO at t=0+ (from i=C
dv/dt; i=0). How could the rate of increase of current in the inductor
be non-zero, but the rate of increase of voltage in the capacitor be
zero? If one is increasing, shouldn't the other as well?
in physical terms and not mathematical. I'll be highly grateful.
Wed Mar 16, 2005 5:28 pm
"Therefore the rate of change of current
in the circuit at t=0+ will be some positive value (from v=L di/dt).
But the rate at which the capacitor voltage is increasing is ZERO at
t=0+ (from i=C dv/dt; i=0)."
How do you get this statement? There
is current charging the capacitor the moment the switch is flipped.
It is limited by R but it is not 0.