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Ltspice question.

Discussion in 'Electronic Design' started by [email protected], Sep 13, 2005.

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  1. Guest

    Hi all.
    I have a simple cct that I want to simulate. Ltspice gives me strange
    behaviour , depending on values in the circuit.


    here is the cct:

    Version 4
    SHEET 1 880 680
    WIRE -128 448 -128 400
    WIRE -32 320 -128 320
    WIRE 80 176 80 144
    WIRE 80 256 80 240
    WIRE 80 320 48 320
    WIRE 144 16 144 -16
    WIRE 144 144 80 144
    WIRE 144 144 144 96
    WIRE 144 176 144 144
    WIRE 144 256 80 256
    WIRE 144 272 144 256
    WIRE 144 448 -128 448
    WIRE 144 448 144 368
    WIRE 160 144 144 144
    WIRE 224 448 144 448
    WIRE 224 464 224 448
    WIRE 288 -16 144 -16
    WIRE 288 96 224 96
    WIRE 288 96 288 -16
    WIRE 352 192 224 192
    WIRE 352 240 352 192
    WIRE 352 448 224 448
    WIRE 352 448 352 320
    WIRE 448 192 352 192
    WIRE 448 240 448 192
    WIRE 448 448 352 448
    WIRE 448 448 448 304
    WIRE 592 -16 288 -16
    WIRE 592 160 592 -16
    WIRE 592 448 448 448
    WIRE 592 448 592 240
    FLAG 224 464 0
    SYMBOL res 128 160 R0
    SYMATTR InstName R1
    SYMATTR Value 2k2
    SYMBOL res 128 0 R0
    SYMATTR InstName R2
    SYMATTR Value 10k
    SYMBOL res 64 304 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R3
    SYMATTR Value 1k
    SYMBOL res 336 224 R0
    SYMATTR InstName R4
    SYMATTR Value 500
    SYMBOL cap 432 240 R0
    SYMATTR InstName C1
    SYMATTR Value 100µ
    SYMBOL voltage 592 144 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 5
    SYMBOL voltage -128 304 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value PULSE(0 5 100u 100n)
    SYMBOL cap 64 176 R0
    SYMATTR InstName C2
    SYMATTR Value 10µ
    SYMBOL npn 80 272 R0
    SYMATTR InstName Q1
    SYMATTR Value 2N2222
    SYMBOL pnp 160 192 M180
    SYMATTR InstName Q2
    SYMATTR Value 2N2907
    TEXT -162 506 Left 0 !.tran 2m


    If I make C2 1 , 2 ,3 ,4 or 5uF the circuit simulates quickly.
    If I make C2 6u or 10u the cct simulates very slowly up to 100uS , then
    runs quickly.If I make it 22u it goes quickly again.
    Why is this happening. I am using the default settings in the control
    panel.
    Cheers
    Rob
     
  2. I read in sci.electronics.design that wrote (in
    Why don't you ask on the LTSpice mailgroup on Yahoo? You have access to
    real experts, and even the author to a limited extent.
     
  3. Guest

    Thanks.Will do.
     
  4. KoKlust

    KoKlust Guest

    If I make C2 1 , 2 ,3 ,4 or 5uF the circuit simulates quickly.
    If I make C2 6u or 10u the cct simulates very slowly up to 100uS , then
    runs quickly.If I make it 22u it goes quickly again.
    Why is this happening. I am using the default settings in the control
    panel.
    Cheers
    Rob


    Hi Rob,

    It is a convergence phenomenon. On my computer, your simulation takes 10.063
    seconds.
    You can help the solver by checking the 'Start external DC supply voltages
    at 0V' checkbox in the 'Simulate/Edit simulation command' window. Then the
    simulation finishes in 0.031 seconds, while giving the same results.

    You can see in the results that it then takes 20 us for the supply voltage
    to linearly ramp up to 5V.

    Best regards,

    Marco
     
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