LtSpice and split supplies :-(

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
Well, I'm no LTspice expert, nor am I one of the people that helped code it. But in my limited experience, the sort of results you've been getting are usually the consequence of imperfect numerical analysis techniques. They're caused, for instance, by iterations in which divisions are performed by a number that is too close to zero, or by the use of floating point variables in the code that do not have enough resolution to obtain an accurate result.

It might be, for instance (and most probably), that the software is internally using 32 bit numbers throughout the code, and that just won't cut it when performing calculations in extreme situations, like your circuit seems to pose.
Maybe (and this is mere speculation from my part) if the program were to be re-compiled to run in a 64 bit environment (with its internal variables also updated to make use of the whole spectrum of the hardware available to the OS) the result of your simulation would be very different.
Seems likely:)
FWIW In my (admittedly limited) experience with said simulator, when LtSpice 'stumbles', ground reference seems to figure into 'the mix' -- I have to wonder, for instance, if the trouble with my circuit is down to a condition whereby the instantaneous bias on a diode (or diodes) momentarily precludes an effective ground path? --- While I've not explored this, it seems plausible considering the 'nodes' complained of in the error message (when it occurs) reference the diodes in the 'lower' doubler --- as you and @Aleph(0) suggest, perhaps it's merely a 'resolution' issue inherent to digital modeling of analog phenomena? --- Anyway, having 'taken five', as it were, my patience has been restored:) --- I genuinely wish to continue my pursuit of proficiency with LtSpice:):):cool:
What the hey! Even as it stands, it's far less annoying than OrCad's simulator - and they don't give that away!:cool::cool::cool:

Sincere thanks for your insight and assistance:)

Best regards
HP
 

cmartinez

Joined Jan 17, 2007
6,890
The place to discuss this is the LTSpice Yahoo group where Mike and Helmut can wrap their collective heads around this. You do know about the yahoo group -- don't you?

https://groups.yahoo.com/neo/groups/LTspice/info
I don't know about HP, but I've known about the yahoo group for quite some time. What I did not know about was this link, which points to a table of contents of many sample circuits and additional parts for the LTspice library. And although it's going to take me a while to study it and sort it out, it seems that I've hit gold thanks to you @Papabravo . Many, many thanks!
 
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Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
The place to discuss this is the LTSpice Yahoo group where Mike and Helmut can wrap their collective heads around this.
That's unfortunate inasmuch as I refuse to give my mobile number to corporate data miners (Cip Yahoo):(
I suppose I could purchase an anonymous "pay as you go phone" for the purpose -- but there's an important principle involved!:mad:

OTOH -- If there's a similar Google Group (Google does not insist upon release of such info) - that'd be do-able?:)

Please know that your input is greatly appreciated!:) --- I hope I don't appear "contrary for contrary's sake" -- Tis merely that I will not be party to the on-going corporate assault upon personal privacy - in principle or practice! To be clear; this is about Yahoo -- not the referenced group:)

Again, thank you!:)
HP
 

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
They must have grandfathered me in before I had such a thing as a mobile number.
Take care to keep your account active! --- My first thought was to 'resurrect' my old Yahoo Acct - unfortunately it had 'permanently expired' owing to long inactivity (which I take to mean no logins):(

Best regards
HP
 

MikeML

Joined Oct 2, 2009
5,444
Not willing to wade thru 50 messages, mostly off topic.

All Spices require that there are no "floating nodes"; every node must have a finite resistance to node 0 (Gnd). Are you sure you have complied with this requirement?
 

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
Not willing to wade thru 50 messages, mostly off topic.

All Spices require that there are no "floating nodes"; every node must have a finite resistance to node 0 (Gnd). Are you sure you have complied with this requirement?
---Emphasis added---

Yes, unless a reverse biased or unbiased diode constitutes a 'loose end', as it were:)

Many thanks!:)
Best regards
HP
 

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
@MikeML

I apologize for the rambling nature of the thread (my fault):(

Attached are two ".asc" files:

"LtSpiceWorks.asc" For the working simulation.
and
"LtSpiceFails.asc" For the erroneous/abortive simulation.

As you may observe, the sole relevant difference in the circuits is the direct/low resistance ground connection (in the working Simulation) vs. the significantly resistive ground connection (in the dysfunctional Simulation)

Advance thanks for any consideration you give this matter!:)


Best regards
HP
 

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Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
Yahoo didn't force me to provide a mobile number.
But it prompts for one when I log on:mad:....I just skip it..:D
When I attempt to register with Yahoo (a prerequisite to joining any Yahoo Group) the registration algorithm insists the Mobile Number field is 'required' and will not accept the 'form' unless provided...:( While I'm tempted to merely enter a 'harmless' number (e.g. directory assistance, etc...) -- I suspect that part of the initial registration process includes response to a 'callback' or SMS message:mad:!

Thanks for your concern!:)

Best regards
HP
 

MikeML

Joined Oct 2, 2009
5,444
Examine this simple circuit:

139.gif

Note the reverse leakage of the default Diode model as the voltage sweeps to -1megV. It can be seen as the voltage at V(b) or I(R2). This sim behaves unnaturally in various ways if a "real" diode is substituted for the default model. Take a look at the LTSpice Help file under the topic D. Diode. Note the default values of some relevant model parameters vs what they are for "real" diodes.

I'm also showing the "noise" at the mostly-floating node C. This sim run was with the simulator settings as shown:

139s.gif

These are values you get with "Reset to Default Values". Playing with Solver, Gmin, Abstol, etc affects V(c).
 

Thread Starter

Hypatia's Protege

Joined Mar 1, 2015
3,214
This sim behaves unnaturally in various ways if a "real" diode is substituted for the default model.
It has been my experience that the default diode behaves quite unexpectedly - even in basic circuits:confused:

Take a look at the LTSpice Help file under the topic D. Diode. Note the default values of some relevant model parameters vs what they are for "real" diodes.
Thanks! Will do!:)

FWIW I often receive this error during a run of "LtSpiceFails.asc" (attached to post #55):
Singular matrix: Check nodes d2#int1 and d4#int1
Iteration #9


Many thanks!:)
HP
 

MikeML

Joined Oct 2, 2009
5,444
I have been a Yahoo Groups member forever. I still receive email digests from several groups I track, but haven't explicitly logged in for a year or so. I just tried it, and it asked for the mobile number, which I left blank. It said my login "failed", but yet I can still access the groups I could previously...
 
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