Voltage across a capacitor ?

K

kristine

Guest
I was modelling a RLC-paralell network in
ORCAD to simulate its natural response.

A natural response is the discharging of either
the capacitor or the inductor (or both) when they are brought
to some DC-value and the source is cut off.

What I find strange is an abrupt change of the voltage
across the capacitor. I expected an exponential waveform for the voltage,
but
the voltage "jumped".
 
"kristine" <kristine.hyvang@chello.no> wrote in message
news:OVEBd.141$VR2.20@amstwist00...
I was modelling a RLC-paralell network in
ORCAD to simulate its natural response.

A natural response is the discharging of either
the capacitor or the inductor (or both) when they are brought
to some DC-value and the source is cut off.

What I find strange is an abrupt change of the voltage
across the capacitor. I expected an exponential waveform for the voltage,
but
the voltage "jumped".
Click to expand...
How much resistance do you have in your model? And where?
 
kristine wrote:
I was modelling a RLC-paralell network in ORCAD to simulate its
natural response.

A natural response is the discharging of either the capacitor or the
inductor (or both) when they are brought to some DC-value and the
source is cut off.

What I find strange is an abrupt change of the voltage across the
capacitor. I expected an exponential waveform for the voltage, but
the voltage "jumped".
Click to expand...
Is this "DC-value" a current source driving the RLC parallel network? A
voltage source will not work very well because L must be 0VDC.
 
"kristine" <kristine.hyvang@chello.no> wrote in message
news:OVEBd.141$VR2.20@amstwist00...
I was modelling a RLC-paralell network in
ORCAD to simulate its natural response.

A natural response is the discharging of either
the capacitor or the inductor (or both) when they are brought
to some DC-value and the source is cut off.

What I find strange is an abrupt change of the voltage
across the capacitor. I expected an exponential waveform for the voltage,
but
the voltage "jumped".
Click to expand...
I've tried different resistor values and different sources.

In the inductor path there is a resistance of 1 Ohm, the paralell branch has
10 Ohm. There is also a 10 Ohm resistance in series with the source (a
VPULSE initially at 1 V falling to zero by some picoseconds).

It still changes the voltage abruptly across the capacitor !?
 
"kristine" <kristine.hyvang@chello.no> wrote in message
news:OVEBd.141$VR2.20@amstwist00...
I was modelling a RLC-paralell network in
ORCAD to simulate its natural response.

A natural response is the discharging of either
the capacitor or the inductor (or both) when they are brought
to some DC-value and the source is cut off.

What I find strange is an abrupt change of the voltage
across the capacitor. I expected an exponential waveform for the voltage,
but
the voltage "jumped".
Click to expand...
The waveform is a damped sinusoid and the voltage across the cap will not
change instantaneously. You must include some resistance in series with the
inductance to insure that the initial conditions do not include an infinite
current in the inductor. Without series resistance the exitation voltage is
divided by zero and most computer programs do not like that. It sounds like
the program is having trouble with your model.
Bob
 
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