I'm having trouble with a PSpice simulation for a relaxation oscillator posted in a previous message on sci.electronics.basics: "PUT Oscillator?"
Terry Pinnell was able to model the oscillator succesfully, using the following netlist:
*Spice netlist for Circuit:
> D:\Docs\Electronics\CIRCUITS\CM\PUT-Diode.CKT
> D1 V1_1 C1_1 D1N914
> V1 V1_1 0 DC 6V
> Q1 Q2_2 Q1_2 V1_1 Q2N2907
> Q2 C1_1 Q2_2 0 Q2N2222
> C1 C1_1 C1_2 20nF
> R2 0 Q1_2 2.2meg
> R1 C1_2 Q1_2 22k
> .SAVE C1_1 C1_2 V1_1 Q2_2 Q1_2 @d1[p] @d1[id] @v1[p] v1#branch @q1[p]
> @q1[ic]
> .SAVE @q1[ib] @q1[ie] @q2[p] @q2[ic] @q2[ib] @q2[ie] @c1[p] @c1[i]
> @r2[p] @r2[i]
> .SAVE @r1[p] @r1[i]
> * Selected Circuit Analyses :
> .OP
> .TRAN 1u 50m 0 1u
> * Models/Subcircuits Used:
> *1N914 100V 80mA Si Switching Diode pkg:DIODE0.4 A,K
> .MODEL D1N914 D(IS=7.075E-9 RS=0.78 N=1.95 TT=7.2E-9 CJO=4E-12
> VJ=0.657
> + M=0.4 BV=100 IBV=0.0001 )
> --
> Terry Pinnell
> Hobbyist, West Sussex, UK
This simulation works correctly for CircuitMaker (using Spice3f5/XSpice). A picture of the results is at http://www.terrypin.dial.pipex.com/Images/Relaxation1.gif
I tried the following netlist in PSpice Lite Version 9.2:
Oscillator
>D1 V1_1 C1_1 D1N914
>V1 V1_1 0 DC 6V
>Q1 Q2_2 Q1_2 V1_1 Q2N2907A
>Q2 C1_1 Q2_2 0 Q2N2222
>C1 C1_1 C1_2 20nF
>R2 0 Q1_2 2.2meg
>R1 C1_2 Q1_2 22k
>.OP
>.TRAN 1u 50m 0 1u
>.lib eval.lib
>.probe
>.end
This circuit does not oscillate. V(C1_1) is 4.9504V, V(C1_2) is 5.293V, VB(Q1) is 5.293V, VB(Q2) is 772.971mV. I(D1) = IC(Q2) = 89.884mA. I(C1) =0. I think that IC(Q2) should discharge C1 but all the current goes through D1 instead.
I was wondering how this circuit is supposed to work, and what possible changes I could make to the PSpice netlist to derive the correct results.