jony130 said:Only LTspic and multisim show the correct answer.
So here we have another example that pspice sometime is wrong
Well I expect the saturation because the positive feedback.LvW said:However, one question: You speak of a "correct answer". What did you expect and what is the correct answer (the same bias point in both cases) ?
flatulent said:You should never totally trust CAD programs. I have had many errors on PSpice over the years. One passive circuit showed the output appearing before the input was applied. A JFET amplifier had gain at X-Ray frequencies.
FvM said:It's really an interesting question, why the Bias Point Solver finds a solution, that won't be observed in a real circuit. I assume, that it's a side effect of the solver's operation method.
I don't regard the solution simply as wrong. Or you can say, it's as wrong as an oscillator simulation that shows no output without an initial disturbance.
I check this and in LT uses the PSpice modelsLvW said:I am pretty sure the reason of the discrepancy is simply that the BJT model in PSpice is not the same as used in both of the other programs.
.model BC549C NPN(Bf=490 Br=2.9 Cjc=5.5p Cje=12p Eg=1.1 Fc=.5 IkF=.1500 Ikr=6 Is=8f Isc=7p Ise=100f Itf=1.4 Mjc=.31 Mje=.7 Nc=1.5 Ne=1.8 Nk=.63
Rc=1.12 Tf=420p Tr=10n Vaf=24 Vjc=.5 Vje=.5 Vtf=12 Xtb=1.5Xtf=50Xti=3)
.model BC557A PNP(Is=10.2f BF=221 VAF=121 Ikf=60M Ise=5.93p Ne=2 Br=4 Nr=1 Var=20
Ikr=90M Re=0.515 Rb=2.06 Rc=0.206 Xtb=1.5 Cje=24.9p Vje=1.1 Mje=0.5 Cjc=8.67p Vjc=0.3 Tf=497p Tr=345n)
jony130 said:.....................
And again LT find a solution (11.2V) that's very different from the PSpice result (0.1V)
It's looks like the LTspice is given more "real life" solution.
I restore the default values in LTspice and surprise surprise result has change.I have simulated your circuit No. 2 (with positive feedback) in LTspice using the same transistors as I have used before in PSpice (but with slightly modified model description) and I got about the same results: Bias point at the ouput without saturation (app 0.1 volts)
It's really interesting, because the noobie in EE will believe the PSpice result and if he build the circuit, he will be looking error in assembling not in the circuit.FvM said:It's really an interesting question, why the Bias Point Solver finds a solution, that won't be observed in a real circuit.
FvM said:To my opinion, one can't expect a generally correct solution from the Bias Point Analysis for a bistable circuit.
I wonder, if Pspice also shows the said results when simulating the a DC transfer function. This could be actually regarded as faulty behaviour.
FvM said:..............
I don't think however, that the mechanical balance analogon really hits. It's rather the case of a ball laying motionless on an inclined plane. Following the analogon, the PSpice solver is ignoring gravity when calculating the solution.
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