Capacitors in series by ngSpice

Discussion in 'General Electronics Chat' started by Nina_, Jan 31, 2013.

  1. Nina_

    Thread Starter New Member

    Dec 11, 2012

    Hi everybody,

    I try to simulate an RLC circuit depicted in the following figure.
    I have noticed that ngspice is not able to compile two capacitors which are connected in series. The netlist is written as follws:
    Code ( (Unknown Language)):
    2. *The global plasma model  
    3. VRF 0 1 SIN(0 100 0.275732)
    4. CBC 2 1 5.25154
    5. Cs 3 2 0.1407107F
    6. RB 4 3 5.25154
    7. LB 5 4 212.692
    8. VG 0 5 dc 10
    9. .END
    this circuit can't be solved transient. I get the following error or warning message :

    Warning: vrf: no DC value, transient time 0 value used Warning: singular matrix: check nodes 2 and 2 Note:
    Starting dynamic gmin stepping

    I would be very grateful, if somebody can give me a Hint on what went wrong. best regard Nina
  2. crutschow


    Mar 14, 2008
    Two capacitors in series don't have a ground path at their junction and Spice can not handle that since the DC level is undefined at that point. Either combine the two capacitors into one equivalent capacitor or place a large (say 100meg ohm) resistor from the junction to ground.

    Note: A 5.25154 farad capacitor is very large.
    Nina_ likes this.
  3. Nina_

    Thread Starter New Member

    Dec 11, 2012
    Hallo Zapper, thank you very much. It works now!