weird LT Spice

John Larkin · 2019-02-06T23:34:22+00:00

I entered a pretty simple pulse driver circuit. It starts with a 5-volt pulse generator V1, has three fets and some passives, and a 12 volt power supply for the output. When I run the transient sim, I can plot the waveform of V1, but no other node. None. If I try to plot any other node, it shows the waveform grid from -10 to +10 mV but no trace. That's weird. Just to test probing things, I added a +1 volt supply all alone off to the side. Then everything worked. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com

weird LT Spice

Feb 06, 2019 23 Replies

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John Larkin 7 years ago

I added a 1 volt supply that was grounded on the low end but not connected otherwise. That temporarily fixed the problem of the un-probeable nodes. But then adding another part broke it again. The power supply just shuffled the circuit a little and stirred up the random initial condition problem. LT Spice is funny that way.

I didn't have floating nodes unless they were inside the EPC fet model. I think that LT Spice doesn't like that model. The EPC library is all text, but it's too complex for me to decode.

John Larkin Highland Technology, Inc lunatic fringe electronics

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legg 7 years ago

If the issue is performance of GaN models, you could always consult the LTspice group on Yahoo.

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I don't recall anyone else having issues with them, but if you've loaded the EPC library somewhere in the past, it may be first reference for the model, even if it or a newer library or model is located in your working library.

The only way to enforce use of local libraries is to use .inc.\xxx.lib rather than the basic .inc xxx.lib

But that's only one possibility.

I ran into this issue with long forgotten non-standard libraries that were decades+ old, resident in a new XVI 'over-install'.

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John Larkin 7 years ago

What's interesting is that I don't have any .inc statement. Spice seems to use the epc.lib file in the local folder just because it's there, or referenced through some path not obvious to me. If I rename it to .liz, it won't run.

John Larkin Highland Technology, Inc lunatic fringe electronics

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legg 7 years ago

That's a good indication that there's only one library, the local one, involved.

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