I have a first-order RC circuit without source and capacitors initially charged to +5 V and -4 V as shown in the figure.

Initially charge sharing takes place between capacitors and v(a) = v(b) = 0.5 V. Then the voltage should get discharged through the resistor exponentially with a time constant of 2RC. But I am observing a linear discharge instantaneously (in ps). Why did this happen?

enter image description here

PS: zero-voltage source was included just to assign initial voltages across capacitors

  • \$\begingroup\$ You should use a "timed" switch (?) ... \$\endgroup\$
    – Antonio51
    Jul 15 at 16:08

1 Answer 1


Your voltage source has zero series resistance so it will charge and discharge the capacitors instantaneously. If you want something different you’ll need a resistor in series with it.

  • \$\begingroup\$ Yeah, charging happens instantaneously. But I am talking about the discharging part. It should be exponential with a time constant of 2RC. But here it is linear. \$\endgroup\$
    – prashanth
    Jul 15 at 15:01
  • \$\begingroup\$ Do you think your voltage source is still zero impedance when it switches to zero? If it switched to a non-zero voltage I would certainly expect that to be the case. \$\endgroup\$
    – Frog
    Jul 15 at 21:25

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