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There are indeed infinitely many reasons for that error. We can't help much unless you let us see more of what you are doing. Upload your .ASC file AND all the other files required to run the simulation, but not .RAW? and .LOG files or pictures,? in a ZIP archive to Files => Temp.

Go to the web page: /g/LTspice/topics. Click on Files in the list on the left. Then click on Temp. Then click on New Upload in the blue box at top left. Click on Upload File in the drop-down menu. Then send a message to tell us that you did that.

Hello everybody,
I'm working on a schematic and encounter a "singular matrix" error.
I know there are as many cause than people in the mankind, but I would like to have advices to avoid this sort of things.
I'm aware that there are a lot of maths in the background too :'(
Thanks a lot in advance for your help.

• Remove voltage sources and replace with "Nortonized" (current) sources.
• Add a small GSHUNT, perhaps 1e-12 to as much as 1e-10.
• Add a small CSHUNT, perhaps 1e-15.
• Use SPICE models for similar (IC or transistor) parts from other manufacturers.

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We can't run it , because:

1. RQ3E100AT_TH symbol has the full path on your computer attached. OK, we can fix that.
2. RQ3E100AT_TH_Thermal.lib is missing
3. ?There is a connection between the body of R3 and the wire labelled Vcc. I suspect that is not correct.
   

Hello John and Andy,

thanks a lot for your replies.

Please, find my circuit here:

/g/LTspice/files/Temp/foldback_switch_groups_io_pascal_plz.zip

Best regards,

Pascal

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You didn't fix the path in RQ3E100AT_TH, but never mind. I can't see what is causing the singular matrix error.

John,

I'm very sorry. I forget to correct paths into symbol and indeed I forget a lib too.

For R3, it wasn't connected to VCC: the wire was too long ;)

I just re-upload the whole schematic:

/g/LTspice/files/Temp/foldback_switch_groups_io_pascal_plz.zip

Thanks a lot in advance.

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I'm very sorry. I forget to correct paths into symbol and indeed I forget a lib too.

For R3, it wasn't connected to VCC: the wire was too long ;)

I just re-upload the whole schematic:

/g/LTspice/files/Temp/foldback_switch_groups_io_pascal_plz.zip

This circuit runs in 24.1.4, but fails in 24.0.12 with a singular matrix error.

Note: there is a pin (A1) on the thermistor, U7, that is disconnected - it's in the body of the symbol. Perhaps it needs connecting to something.

--
Regards,
Tony

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I'm very sorry. I forget to correct paths into symbol and indeed I forget a lib too.

For R3, it wasn't connected to VCC: the wire was too long ;)

I just re-upload the whole schematic:

/g/LTspice/files/Temp/foldback_switch_groups_io_pascal_plz.zip

Are you sure? U2 and J2 are correct?

U2 is configured as an inverting amplifier and is connected to node OUT, which must always be positive. Therefore, U2's output should go negative, but it can't because it doesn't have a negative power rail, it is grounded.

Did you test each stage before connecting it all together?

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thanks a lot for your reply.

Indeed, it's an inverting amplifier.

But if you look closer, no need to negative supply as the amplifier positive input is connected to mid-supply: it acts as a "virtual ground".

I first tested the whole schematic without PTC and it "works" :)

Sorry. Yes, you're right.

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Thanks a lot for your reply.

Indeed, it's an inverting amplifier.

But if you look closer, no need to negative supply as the amplifier positive input is connected to mid-supply: it acts as a "virtual ground".

I first tested the whole schematic without PTC and it "works" :)

I tested the whole schematic by removing the PTC and with R2 grounded, in a .OP analysis, and it didn't work in either 24.0.12 or 24.1.5 , although the errors are different:

24.1.5

Convergence Failure:? Time step too small; initial timepoint: trouble with instance "J2"

24.0.12

Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 4
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Singular matrix:? Check nodes v2#branch and u2:vn
?? Iteration No. 1
Starting source stepping with srcstepmethod=1
Source Step = 3.0303%
Source stepping failed

Singular matrix:? Check nodes u2:vn and u2:vp
?? Iteration No. 4
Fatal Error: Singular matrix:? check nodes u2:vn and u2:vp
?? Iteration No. 4

You can't conclude much from the errors.

If I also remove J1 as well, the circuit does simulate in 24.1.x, but not in 24.0.12 and foldback occurs at ~7.7A.

Hope that's helpful.

--
Regards,
Tony

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thanks a lot for your reply.

Indeed, it's an inverting amplifier.

But if you look closer, no need to negative supply as the amplifier positive input is connected to mid-supply: it acts as a "virtual ground".

I first tested the whole schematic without PTC and it "works" :)

Update:

Change V2 from 13VDC to:

PULSE(0 13 0 100u 0 1 2 1)

.. and the whole simulation works OK in both 24.0.12 and 24.1.5. You might also try using the "startup" switch in the .TRAN directive, which also works:

.TRAN 1 startup

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I hope you're doing well ?

Thanks you so much for your help, indeed it works on my side too with "startup" option.

How did you find that ? It's almost magic for me :)

However, I didn't try yet with PULSE(0 13 0 100u 0 1 2 1)

I tried with another PTC model and it does the "singular matrix" error again.

But it was worth a try !

Thanks you so much, I keep on :)

The clue was that LTspice always failed to find the initial solution, i.e. the matrix state at time=0, rather than failure mid-way through the analysis, which is what happens in some problems.

From the point of view of this schematic, the difference is that with the "startup" switch, all DC voltage sources start at 0 and ramp up over the initial 20μs just like a real power supply (well, much faster, really), whereas if you use a "virtual" startup condition by using a pulse specification, you can do this one DC source at a time. Obviously, "startup" is much simpler to do.

I don't know where the exact problem was, since you say that all parts tested OK on their own. Sometimes the solution to a problem is more important than a complete understanding of the problem itself.? ;-)

--
Regards,
Tony