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I'm studying for my electrical circuits exam and since Eagle is used for some future exams I thought I could learn it and double-check my calculations by simulating with Eagle.

I'm trying to simulate the following circuit, but Eagle is giving me a "singular matrix warning" and failing to simulate. It's also telling me to "check nodes l_l2#branch and l_l2#branch" but I don't know how which nodes those are, or how to get nodes' names.

I searched for this error and what I found concerned voltage sources in a loop (only one source here) or infinite impedance branches (there shouldn't be any). Why isn't the simulation running? Thanks in advance!

Netlist:

* SpiceNetList
* 
* Exported from Main.sch at 5/12/19 12:37 PM
* 
* EAGLE Version 9.4.0 Copyright (c) 1988-2019 Autodesk, Inc.
* 
.TEMP=25.0

* --------- .OPTIONS ---------
.OPTIONS ABSTOL=1e-12 GMIN=1e-12 PIVREL=1e-3 ITL1=100 ITL2=50 PIVTOL=1e-13 RELTOL=1e-3 VNTOL=1e-6 CHGTOL=1e-15 ITL4=10 METHOD=TRAP SRCSTEPS=0 TRTOL=7 NODE

* --------- .PARAMS ---------

* --------- devices ---------
V_V1 N_1 0 DC 1V AC 1V 
R_R2 0 N_1 4 
L_L1 0 N_3 20m 
L_L2 0 N_1 20m 
R_R1 N_3 N_1 2 

* --------- simulation ---------
.control
set filetype=ascii
OP
write Main.sch.sim
.endc



.END

Schematic:circuit schematic

P.S. Are there any good Eagle tutorials out there focused on SPICE simulation? Moreover, Eagle only allows simulating DC/AC sweeps, transients or at operating point. How do I simulate a constant-frequency AC source?

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  • \$\begingroup\$ the inductor is shorting the voltage source. \$\endgroup\$
    – analogsystemsrf
    May 12, 2019 at 10:52
  • \$\begingroup\$ Which inductor, and how would I go about fixing this? I don't see any short-circuit in the schematic and I copied it verbatim from the professor's handout... \$\endgroup\$
    – kmf
    May 12, 2019 at 10:56
  • \$\begingroup\$ If you cannot see that L2 is across your voltage source, perhaps this is a good time to practice redrawing the circuit to get familiar with seeing parallel and series connections. \$\endgroup\$
    – Tyler
    May 12, 2019 at 11:36
  • \$\begingroup\$ Add a tiny resistance in series with L2. \$\endgroup\$
    – Chu
    May 12, 2019 at 12:32
  • \$\begingroup\$ Got it, thank you. So this is a shortcoming of ngspice's capabilities, it can't simulate ideal circuits? (makes sense) How would I go about solving it? Adding a small resistor in series? EDIT: @Chu, didn't see your comment. I'll try, thank you! \$\endgroup\$
    – kmf
    May 12, 2019 at 12:38

1 Answer 1

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The problem is that you have asked for an operating point (OP) analysis which is a dc simulation, regardless of whether your voltage source is intended to be an ac source. So, the inductor L2 is shorting the voltage source.

I have no experience with how Eagle does simulations, but there may be an option to skip the OP. You might then be able to run a transient simulation, if you want to see voltage and current as a function of time. If you only want to see the magnitude and phase of ac signals then run an "AC sweep"...you can usually have that run at a single frequency rather than sweep the frequency.

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  • \$\begingroup\$ Thank you! If I try to make it run at a single frequency, however, Eagle tells me that end frequency must be greater than starting frequency. Moreover, if I try to run an AC sweep, the error is still there :( \$\endgroup\$
    – kmf
    May 12, 2019 at 12:40
  • \$\begingroup\$ It sounds like you will have to add a small resistance in series with L2. Try 0.001 ohm and see if that helps. Yes, your ac results will be a bit incorrect, but the other option is to use a different simulator. \$\endgroup\$
    – Elliot Alderson
    May 12, 2019 at 12:44
  • \$\begingroup\$ Works. Thank you! \$\endgroup\$
    – kmf
    May 12, 2019 at 13:36

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