LTspice weirdness

Jul 05, 2026 Last reply: 2 weeks ago 5 Replies
P

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Hi, all,



I'm working on a charge amp for a short-wave UV photodetection system. LTspice goes nuts trying to simulate it for 1.5 ms or more. It works fine up to 1.499999ms.



The attached .asc file has a somewhat stylized version of the front end, using only LTspice built-in parts and with not a lot of bias control.



Changing ".tran 1.499ms" to .tran 1.5ms" changes its behavior completely. This is using version 1.72, with all the default values for control panel settings. The Win32 version looks much the same.



Weird.



Cheers



Phil Hobbs


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J

Try adding a 1 ohm resistor off to the side. Ground one end.

And the Gear solver seems more willing to go.

.opt abstol=20n .opt chgtol=20p .opt method=gear

or something like that.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

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P

Didn’t help when I did it.

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P

Turns out that switching to straight trapezoidal *and* settinga short minimum time step more or less fixes it.

Thanks for the nudge!

Cheers

Phil Hobbs

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J

LT lets you set a max time step but not a min.

Pity. It can spend all afternoon stepping femtoseconds.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

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