gEDA-user: problem to simulate an astable multivibrator with uA741 opamp

[joseda <josedaniel_martinez@xxxxxxxx>]

I'm trying to simulate an astable multivibrator with ngspice, but the graphic
i get is odd. I simulated the same circuit with qucs and ¡ didn't have any
problem. I'm trying to figure out where the problem is.

This is the netlist:

*********************************************************
*vvvvvvvv  Included SPICE model from uA741.lib vvvvvvvv
* Model for uA741 Op Amp (from EVAL library in PSpice)
* connections:   non-inverting input
*                | inverting input
*                | | positive power supply
*                | | | negative power supply
*                | | | | output
*                | | | | |
*
.subckt uA741    1 2 3 4 5
*
  c1   11 12 8.661E-12
  c2    6  7 30.00E-12
  dc    5 53 dy
  de   54  5 dy
  dlp  90 91 dx
  dln  92 90 dx
  dp    4  3 dx
  egnd 99  0 poly(2),(3,0),(4,0) 0 .5 .5
  fb    7 99 poly(5) vb vc ve vlp vln 0 10.61E6 -1E3 1E3 10E6 -10E6
  ga    6  0 11 12 188.5E-6
  gcm   0  6 10 99 5.961E-9
  iee  10  4 dc 15.16E-6
  hlim 90  0 vlim 1K
  q1   11  2 13 qx
  q2   12  1 14 qx
  r2    6  9 100.0E3
  rc1   3 11 5.305E3
  rc2   3 12 5.305E3
  re1  13 10 1.836E3
  re2  14 10 1.836E3
  ree  10 99 13.19E6
  ro1   8  5 50
  ro2   7 99 100
  rp    3  4 18.16E3
  vb    9  0 dc 0
  vc    3 53 dc 1
  ve   54  4 dc 1
  vlim  7  8 dc 0
  vlp  91  0 dc 40
  vln   0 92 dc 40
.model dx D(Is=800.0E-18 Rs=1)
.model dy D(Is=800.00E-18 Rs=1m Cjo=10p)
.model qx NPN(Is=800.0E-18 Bf=93.75)
.ends
*^^^^^^^^  End of included SPICE model from uA741.lib ^^^^^^^^
*
*==============  Begin SPICE netlist of main design ============
V2 Vcc 0 DC 15V
R3 3 1 50k  
R2 0 1 2.2k  
R1 2 3 50k  
C1 0 2 1u  
XU1 1 2 Vcc -Vcc 3 uA741
.control
tran 0.1m 30m
plot v(3)
.endc
.end

The graphic i get is like this:
http://img152.imageshack.us/my.php?image=ngspice.jpg

The voltage drop below 400V what's the problem?!!

Thanks in advance



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