LTSpice: Failed to find DC Operating point for AC-Analysis in complex feedback circuit

Hi forum,

I have a quite complex feedback circuit which is impossible to simulate under LTSpice. The circuit's aim is a pushpull stage with current regulation. The current is sensed via U4 and U5, their output is led via current-mirrors to the transimpedance amplifier U6 which creates a voltage signal. This voltage signal is fed into the error amplifier U1 which again drives the push-pull-stage.

When I run the step analysis the LTSpice takes forever. With AC-Analysis I am not successful neither. Running the AC-Analysis I can cancel the simulation and I get the error: Failed to find DC Operating point for AC-Analysis

Do you have any idea how to get any result from the simulation?

Top Replies

    •  Analog Employees 
    Dec 30, 2020 +1 suggested

    Hi pioupus,

    I wished you had attached your circuit (*.asc file) to the post. To do so, you have to use "Insert", "image/video/file", and then click on "upload" to attach your LTspice simulation file so…

    •  Analog Employees 
    Mar 12, 2021 in reply to pggood +1 verified

    pggood

    Please use insert -> image/video/file to attach the asc files.  

  • 0
    •  Analog Employees 
    on Dec 30, 2020 8:36 PM

    Hi pioupus,

    I wished you had attached your circuit (*.asc file) to the post. To do so, you have to use "Insert", "image/video/file", and then click on "upload" to attach your LTspice simulation file so maybe someone can help with the simulation not executing.

    Regards,

    Hooman

  • Im having the same issue

    This will run 

    Version 4
    SHEET 1 948 680
    WIRE 752 -224 576 -224
    WIRE 752 -208 608 -208
    WIRE 576 -192 576 -224
    WIRE 576 -192 208 -192
    WIRE 880 -192 816 -192
    WIRE 752 -176 704 -176
    WIRE 768 -160 768 -176
    WIRE 544 -144 448 -144
    WIRE 608 -144 608 -208
    WIRE 608 -144 544 -144
    WIRE 448 -112 448 -144
    WIRE 448 -112 416 -112
    WIRE 208 -64 208 -192
    WIRE 208 -64 160 -64
    WIRE 320 -64 208 -64
    WIRE 96 -48 -16 -48
    WIRE 112 -32 112 -48
    WIRE 320 -16 320 -32
    WIRE 576 0 576 -192
    WIRE 544 16 544 -144
    WIRE 576 16 544 16
    WIRE -16 32 -144 32
    WIRE 576 48 544 48
    WIRE 704 48 704 -176
    WIRE 704 48 640 48
    WIRE 592 80 592 64
    WIRE 64 112 -16 112
    WIRE 448 112 416 112
    WIRE -16 128 -16 112
    WIRE 208 160 128 160
    WIRE 320 160 208 160
    WIRE 448 176 448 112
    WIRE 544 176 544 48
    WIRE 544 176 448 176
    WIRE 624 176 544 176
    WIRE 80 192 80 176
    WIRE -144 208 -144 32
    WIRE -128 208 -144 208
    WIRE -16 208 -128 208
    WIRE 320 208 320 192
    WIRE -128 224 -128 208
    WIRE 208 256 208 160
    WIRE 576 256 576 64
    WIRE 576 256 208 256
    WIRE 704 256 704 48
    WIRE 784 256 704 256
    WIRE 624 288 624 176
    WIRE 784 288 624 288
    WIRE 576 304 576 256
    WIRE 784 304 576 304
    WIRE 880 304 848 304
    WIRE 800 336 800 320
    FLAG -128 224 0
    FLAG 112 -32 0
    FLAG 80 192 0
    FLAG 320 -16 0
    FLAG 320 208 0
    FLAG 592 80 0
    FLAG 768 -160 0
    FLAG 800 336 0
    SYMBOL voltage -16 112 R0
    WINDOW 123 24 124 Left 2
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value ""
    SYMATTR Value2 AC 10
    SYMBOL voltage -16 -64 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value SINE(0 10 12K)
    SYMBOL Digital\\or 128 -144 R0
    SYMATTR InstName A1
    SYMBOL Digital\\or 96 80 R0
    SYMATTR InstName A2
    SYMBOL Digital\\srflop 368 -160 R0
    SYMATTR InstName A3
    SYMBOL Digital\\srflop 368 64 R0
    SYMATTR InstName A4
    SYMBOL Digital\\or 608 -32 R0
    SYMATTR InstName A5
    SYMBOL Digital\\or 784 -272 R0
    SYMATTR InstName A6
    SYMBOL Digital\\or 816 224 R0
    SYMATTR InstName A7
    TEXT -50 256 Left 2 !.ac lin 200 11K 13K

    When I add 2 wires from the output back to the input or gates

    Version 4
    SHEET 1 948 680
    WIRE 880 -320 32 -320
    WIRE 752 -224 576 -224
    WIRE 752 -208 608 -208
    WIRE 576 -192 576 -224
    WIRE 576 -192 208 -192
    WIRE 880 -192 880 -320
    WIRE 880 -192 816 -192
    WIRE 752 -176 704 -176
    WIRE 768 -160 768 -176
    WIRE 544 -144 448 -144
    WIRE 608 -144 608 -208
    WIRE 608 -144 544 -144
    WIRE 32 -112 32 -320
    WIRE 96 -112 32 -112
    WIRE 448 -112 448 -144
    WIRE 448 -112 416 -112
    WIRE 208 -64 208 -192
    WIRE 208 -64 160 -64
    WIRE 320 -64 208 -64
    WIRE 96 -48 -16 -48
    WIRE 112 -32 112 -48
    WIRE 320 -16 320 -32
    WIRE 576 0 576 -192
    WIRE 544 16 544 -144
    WIRE 576 16 544 16
    WIRE -16 32 -144 32
    WIRE 576 48 544 48
    WIRE 704 48 704 -176
    WIRE 704 48 640 48
    WIRE 592 80 592 64
    WIRE 64 112 -16 112
    WIRE 448 112 416 112
    WIRE -16 128 -16 112
    WIRE 208 160 128 160
    WIRE 320 160 208 160
    WIRE 64 176 32 176
    WIRE 448 176 448 112
    WIRE 544 176 544 48
    WIRE 544 176 448 176
    WIRE 624 176 544 176
    WIRE 80 192 80 176
    WIRE -144 208 -144 32
    WIRE -128 208 -144 208
    WIRE -16 208 -128 208
    WIRE 320 208 320 192
    WIRE -128 224 -128 208
    WIRE 208 256 208 160
    WIRE 576 256 576 64
    WIRE 576 256 208 256
    WIRE 704 256 704 48
    WIRE 784 256 704 256
    WIRE 624 288 624 176
    WIRE 784 288 624 288
    WIRE 576 304 576 256
    WIRE 784 304 576 304
    WIRE 880 304 848 304
    WIRE 800 336 800 320
    WIRE 32 416 32 176
    WIRE 880 416 880 304
    WIRE 880 416 32 416
    FLAG -128 224 0
    FLAG 112 -32 0
    FLAG 80 192 0
    FLAG 320 -16 0
    FLAG 320 208 0
    FLAG 592 80 0
    FLAG 768 -160 0
    FLAG 800 336 0
    SYMBOL voltage -16 112 R0
    WINDOW 123 24 124 Left 2
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value ""
    SYMATTR Value2 AC 10
    SYMBOL voltage -16 -64 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value SINE(0 10 12K)
    SYMBOL Digital\\or 128 -144 R0
    SYMATTR InstName A1
    SYMBOL Digital\\or 96 80 R0
    SYMATTR InstName A2
    SYMBOL Digital\\srflop 368 -160 R0
    SYMATTR InstName A3
    SYMBOL Digital\\srflop 368 64 R0
    SYMATTR InstName A4
    SYMBOL Digital\\or 608 -32 R0
    SYMATTR InstName A5
    SYMBOL Digital\\or 784 -272 R0
    SYMATTR InstName A6
    SYMBOL Digital\\or 816 224 R0
    SYMATTR InstName A7
    TEXT -50 256 Left 2 !.ac lin 200 11K 13K

    I get an error 

    Circuit: * D:\pll\freq_Phase2.asc

    Direct Newton iteration failed to find .op point. (Use ".option noopiter" to skip.)
    Starting Gmin stepping
    Gmin = 10
    Gmin = 1.07374
    vernier = 0.5
    vernier = 0.25
    vernier = 0.125
    vernier = 0.0625
    Gmin = 0.995033
    vernier = 0.03125
    vernier = 0.015625
    vernier = 0.0078125
    vernier = 0.00390625
    Gmin = 0.999816
    vernier = 0.00195313
    vernier = 0.000976563
    vernier = 0.000488281
    Gmin = 0
    Gmin stepping failed

    Starting source stepping with srcstepmethod=0
    Could not converge to DC with sources off!
    Starting source stepping with srcstepmethod=1
    Could not converge to DC with sources off!
    Pseudo Transient failed in finding the operating point at 0 s.
    Fatal Error: Failed to find DC operating point for AC analysis.

  • 0
    •  Analog Employees 
    on Mar 11, 2021 11:24 PM in reply to pggood

    Hi pggood,

    I recommend you attach the LTspice *.asc file here (along with any special components you may have in your netlist).

    Use, Insert, Upload to attach your circuit and any images you may want to show.

    It's not easy to look at your spice text and figure out what's going on.

    Regards,

    Hooman

  • The TXT is the 

    Original.asc

    ______________________________________

    Version 4
    SHEET 1 948 680
    WIRE 752 -224 576 -224
    WIRE 752 -208 608 -208
    WIRE 576 -192 576 -224
    WIRE 576 -192 208 -192
    WIRE 880 -192 816 -192
    WIRE 752 -176 704 -176
    WIRE 768 -160 768 -176
    WIRE 544 -144 448 -144
    WIRE 608 -144 608 -208
    WIRE 608 -144 544 -144
    WIRE 448 -112 448 -144
    WIRE 448 -112 416 -112
    WIRE 208 -64 208 -192
    WIRE 208 -64 160 -64
    WIRE 320 -64 208 -64
    WIRE 96 -48 -16 -48
    WIRE 112 -32 112 -48
    WIRE 320 -16 320 -32
    WIRE 576 0 576 -192
    WIRE 544 16 544 -144
    WIRE 576 16 544 16
    WIRE -16 32 -144 32
    WIRE 576 48 544 48
    WIRE 704 48 704 -176
    WIRE 704 48 640 48
    WIRE 592 80 592 64
    WIRE 64 112 -16 112
    WIRE 448 112 416 112
    WIRE -16 128 -16 112
    WIRE 208 160 128 160
    WIRE 320 160 208 160
    WIRE 448 176 448 112
    WIRE 544 176 544 48
    WIRE 544 176 448 176
    WIRE 624 176 544 176
    WIRE 80 192 80 176
    WIRE -144 208 -144 32
    WIRE -128 208 -144 208
    WIRE -16 208 -128 208
    WIRE 320 208 320 192
    WIRE -128 224 -128 208
    WIRE 208 256 208 160
    WIRE 576 256 576 64
    WIRE 576 256 208 256
    WIRE 704 256 704 48
    WIRE 784 256 704 256
    WIRE 624 288 624 176
    WIRE 784 288 624 288
    WIRE 576 304 576 256
    WIRE 784 304 576 304
    WIRE 880 304 848 304
    WIRE 800 336 800 320
    FLAG -128 224 0
    FLAG 112 -32 0
    FLAG 80 192 0
    FLAG 320 -16 0
    FLAG 320 208 0
    FLAG 592 80 0
    FLAG 768 -160 0
    FLAG 800 336 0
    SYMBOL voltage -16 112 R0
    WINDOW 123 24 124 Left 2
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value ""
    SYMATTR Value2 AC 10
    SYMBOL voltage -16 -64 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value SINE(0 10 12K)
    SYMBOL Digital\\or 128 -144 R0
    SYMATTR InstName A1
    SYMBOL Digital\\or 96 80 R0
    SYMATTR InstName A2
    SYMBOL Digital\\srflop 368 -160 R0
    SYMATTR InstName A3
    SYMBOL Digital\\srflop 368 64 R0
    SYMATTR InstName A4
    SYMBOL Digital\\or 608 -32 R0
    SYMATTR InstName A5
    SYMBOL Digital\\or 784 -272 R0
    SYMATTR InstName A6
    SYMBOL Digital\\or 816 224 R0
    SYMATTR InstName A7
    TEXT -50 256 Left 2 !.ac lin 200 11K 13K

    ______________________________________

    notworking.asc

    _____________________________________________________

    Version 4
    SHEET 1 948 680
    WIRE 880 -320 32 -320
    WIRE 752 -224 576 -224
    WIRE 752 -208 608 -208
    WIRE 576 -192 576 -224
    WIRE 576 -192 208 -192
    WIRE 880 -192 880 -320
    WIRE 880 -192 816 -192
    WIRE 752 -176 704 -176
    WIRE 768 -160 768 -176
    WIRE 544 -144 448 -144
    WIRE 608 -144 608 -208
    WIRE 608 -144 544 -144
    WIRE 32 -112 32 -320
    WIRE 96 -112 32 -112
    WIRE 448 -112 448 -144
    WIRE 448 -112 416 -112
    WIRE 208 -64 208 -192
    WIRE 208 -64 160 -64
    WIRE 320 -64 208 -64
    WIRE 96 -48 -16 -48
    WIRE 112 -32 112 -48
    WIRE 320 -16 320 -32
    WIRE 576 0 576 -192
    WIRE 544 16 544 -144
    WIRE 576 16 544 16
    WIRE -16 32 -144 32
    WIRE 576 48 544 48
    WIRE 704 48 704 -176
    WIRE 704 48 640 48
    WIRE 592 80 592 64
    WIRE 64 112 -16 112
    WIRE 448 112 416 112
    WIRE -16 128 -16 112
    WIRE 208 160 128 160
    WIRE 320 160 208 160
    WIRE 64 176 32 176
    WIRE 448 176 448 112
    WIRE 544 176 544 48
    WIRE 544 176 448 176
    WIRE 624 176 544 176
    WIRE 80 192 80 176
    WIRE -144 208 -144 32
    WIRE -128 208 -144 208
    WIRE -16 208 -128 208
    WIRE 320 208 320 192
    WIRE -128 224 -128 208
    WIRE 208 256 208 160
    WIRE 576 256 576 64
    WIRE 576 256 208 256
    WIRE 704 256 704 48
    WIRE 784 256 704 256
    WIRE 624 288 624 176
    WIRE 784 288 624 288
    WIRE 576 304 576 256
    WIRE 784 304 576 304
    WIRE 880 304 848 304
    WIRE 800 336 800 320
    WIRE 32 416 32 176
    WIRE 880 416 880 304
    WIRE 880 416 32 416
    FLAG -128 224 0
    FLAG 112 -32 0
    FLAG 80 192 0
    FLAG 320 -16 0
    FLAG 320 208 0
    FLAG 592 80 0
    FLAG 768 -160 0
    FLAG 800 336 0
    SYMBOL voltage -16 112 R0
    WINDOW 123 24 124 Left 2
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value ""
    SYMATTR Value2 AC 10
    SYMBOL voltage -16 -64 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V2
    SYMATTR Value SINE(0 10 12K)
    SYMBOL Digital\\or 128 -144 R0
    SYMATTR InstName A1
    SYMBOL Digital\\or 96 80 R0
    SYMATTR InstName A2
    SYMBOL Digital\\srflop 368 -160 R0
    SYMATTR InstName A3
    SYMBOL Digital\\srflop 368 64 R0
    SYMATTR InstName A4
    SYMBOL Digital\\or 608 -32 R0
    SYMATTR InstName A5
    SYMBOL Digital\\or 784 -272 R0
    SYMATTR InstName A6
    SYMBOL Digital\\or 816 224 R0
    SYMATTR InstName A7
    TEXT -50 256 Left 2 !.ac lin 200 11K 13K

    __________________________

  • +1
    •  Analog Employees 
    on Mar 12, 2021 2:29 AM in reply to pggood

    Please use insert -> image/video/file to attach the asc files.