On Mon, 14 May 2018 07:12:36 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:
>On Sun, 13 May 2018 21:12:13 -0700 (PDT), evelyn.kreps74@gmail.com
>wrote:
>
>>https://support.google.com/photos/thread/115943?msgid=115982
>
>"Update required"
>
>Update of what?
>
>Google is evil. Post pix to Dropbox or something.
>
>I recently made a pulse generator using a Cree SiC fet. Their Spice
>model assumes zero forward recovery time of the substrate diode.
>Wrong.
Spice Modeling of forward AND reverse recovery is difficult due to
lack of real data. Thus my original post...
Message-ID: <tomv8clnib23d5t57t39p4esi2vi5v09bi@4ax.com>
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions,
by understanding what nature is hiding.
"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie
Reply by John Larkin●May 14, 20182018-05-14
On Sun, 13 May 2018 21:12:13 -0700 (PDT), evelyn.kreps74@gmail.com
wrote:
"Update required"
Update of what?
Google is evil. Post pix to Dropbox or something.
I recently made a pulse generator using a Cree SiC fet. Their Spice
model assumes zero forward recovery time of the substrate diode.
Wrong.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
On Mon, 06 Feb 2017 10:16:43 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>On Sun, 5 Feb 2017 19:01:04 -0800 (PST), bill.sloman@ieee.org wrote:
>
>>On Monday, February 6, 2017 at 3:07:19 AM UTC+11, Jim Thompson wrote:
>
>[snip]
>>
>>> I would suggest you check out the accuracy of the resident Spice
>>> models... all based on nearly ideal approximations to emphasize
>>> simulation speed... not accuracy.
>>
>>Gummell-Poon is pretty accurate, where it works. VBIC - which LTSpice will run - is supposed to be better, if you can get the parameters for a specific part. Semiconductor manufacturers treat them as trade secrets.
>
>Most of the foundries I deal with (that have processes with bipolar
>devices) _do_ provide VBIC models (PSpice runs them as well).
>
>Unfortunately most _discrete_ device manufacturers don't provide
>adequate models, if they provide any at all.
>
> ...Jim Thompson
You missed that my point was about LTspice... LTspice's default models
are gross simplifications.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
Reply by Jim Thompson●February 6, 20172017-02-06
On Sun, 5 Feb 2017 19:01:04 -0800 (PST), bill.sloman@ieee.org wrote:
>On Monday, February 6, 2017 at 3:07:19 AM UTC+11, Jim Thompson wrote:
[snip]
>
>> I would suggest you check out the accuracy of the resident Spice
>> models... all based on nearly ideal approximations to emphasize
>> simulation speed... not accuracy.
>
>Gummell-Poon is pretty accurate, where it works. VBIC - which LTSpice will run - is supposed to be better, if you can get the parameters for a specific part. Semiconductor manufacturers treat them as trade secrets.
Most of the foundries I deal with (that have processes with bipolar
devices) _do_ provide VBIC models (PSpice runs them as well).
Unfortunately most _discrete_ device manufacturers don't provide
adequate models, if they provide any at all.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
Reply by ●February 5, 20172017-02-05
On Monday, February 6, 2017 at 3:07:19 AM UTC+11, Jim Thompson wrote:
> On Sat, 4 Feb 2017 09:08:44 -0600, "Tim Williams"
> <tiwill@seventransistorlabs.com> wrote:
[snip]
> It struck me that most of the lurkers on this group are engineers.
>
> All that an engineer cares about in regard to a Spice model is that
> it's terminal behavior be the same as the real device behaves in his
> system/PCB.
>
> The engineer doesn't give a damn whether the model duplicates the
> actual physics of the device or not, only that it performs properly.
>
> I would argue that attempting to model a device following the complete
> physics of a device produces a cumbersome, difficult to converge and
> slow-to-simulate model.
Not necessarily.
> I have 55 "learned"/peer-reviewed papers in my
> forward-overshoot/reverse-recovery research file that demonstrate my
> point ;-)
>
> I would point out, for instance, that the Spice model for a bipolar
> device is not a model that conveys the actual physics of the device,
> but a simulatablely-tractable approximation.
Gummel-Poon doesn't capture inverted transistor behaviour that makes Baxandall class-D oscillators "squeg" when built with bipolar transistors and a too-big feed inductor.
> The elitists amongst us would insist that a proper model can't be
> created unless it "solves" the underlying physics equations.
>
> That is nonsense.
It is. A proper model must respect the underlying physics as much as it can - and the underlying physics is often a royal route to a good model - but - as the Gummel-Poon example makes clear - an imperfect model can often be very useful.
It's nice if it's imperfections are spelled out, as they rarely are.
> In my musing, not even committed to paper yet, just rolling the
> function around in my head, I realized that a controlled charge
> accumulation, metered release could easily model the sacred SRD... no
> solution of a transport equation involved.
Phil Hobbs did spell out why this might not work as well as you like to think, and might have given you a clue to an approach that might work better.
> When I posted the waveforms of my forward recovery model, the resident
> pompous asshole reared his ugly head and pronounced, "...only
> waveforms".
Waveforms are the integrated output of complex processes. A waveform has one value at one moment. The process that generates the waveform has several variables all of which are varying with time.
> Sonnuva gun, I do believe that's what engineers want to see on their
> simulator and their 'scope... not a scrolling useless paper extolling
> that the physics equation has been solved.
That's what they want to see. This doesn't mean that it's what they ought to be looking for.
> Lastly, I think many people here are using LTspice, and the elitists
> and the resident pompous asshole hang their hats on the results...
We all know that LTSpice outputs can be misleading. The trick is to know when, where and why.
> I would suggest you check out the accuracy of the resident Spice
> models... all based on nearly ideal approximations to emphasize
> simulation speed... not accuracy.
Gummell-Poon is pretty accurate, where it works. VBIC - which LTSpice will run - is supposed to be better, if you can get the parameters for a specific part. Semiconductor manufacturers treat them as trade secrets.
--
Bill Sloman, Sydney
Reply by Jim Thompson●February 5, 20172017-02-05
On Sat, 4 Feb 2017 09:08:44 -0600, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:
[snip]
[replying to Phil Hobbs]...
>
>So I don't get your obsession with analytical accuracy. You're being a
>useless dick about it. If all your PhD has to say is "can't be done", then
>would you please step out of this conversation while the engineers discuss
>the "well what if..."?
>
>Please do correct me if I'm wrong about any of these things: the value of an
>analytical 1N914 model, or a rectifier, or PD, or the reasons for your
>obstinance.
>
>Cheers,
>
>Tim
Over dinner last night I was musing about Spice models, my diode model
covering forward overshoot and the resulting hysteria amongst the
"elite".
It struck me that most of the lurkers on this group are engineers.
All that an engineer cares about in regard to a Spice model is that
it's terminal behavior be the same as the real device behaves in his
system/PCB.
The engineer doesn't give a damn whether the model duplicates the
actual physics of the device or not, only that it performs properly.
I would argue that attempting to model a device following the complete
physics of a device produces a cumbersome, difficult to converge and
slow-to-simulate model.
I have 55 "learned"/peer-reviewed papers in my
forward-overshoot/reverse-recovery research file that demonstrate my
point ;-)
I would point out, for instance, that the Spice model for a bipolar
device is not a model that conveys the actual physics of the device,
but a simulatablely-tractable approximation.
The elitists amongst us would insist that a proper model can't be
created unless it "solves" the underlying physics equations.
That is nonsense.
In my musing, not even committed to paper yet, just rolling the
function around in my head, I realized that a controlled charge
accumulation, metered release could easily model the sacred SRD... no
solution of a transport equation involved.
When I posted the waveforms of my forward recovery model, the resident
pompous asshole reared his ugly head and pronounced, "...only
waveforms".
Sonnuva gun, I do believe that's what engineers want to see on their
simulator and their 'scope... not a scrolling useless paper extolling
that the physics equation has been solved.
Lastly, I think many people here are using LTspice, and the elitists
and the resident pompous asshole hang their hats on the results...
I would suggest you check out the accuracy of the resident Spice
models... all based on nearly ideal approximations to emphasize
simulation speed... not accuracy.
HTH >:-}
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.
Reply by John Larkin●February 4, 20172017-02-04
On Sat, 04 Feb 2017 17:32:26 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:
>On Sat, 4 Feb 2017 16:29:42 -0800 (PST), pcdhobbs@gmail.com wrote:
>
>>>Nothing is impossible to model with Spice.
>>>Watch this space >:-}
>>
>>Wow, between that and the Donald, I may OD on popcorn. ;)
>>
>>Cheers
>>
>>Phil Hobbs
>
>I did that last night... and now I am suffering some intestinal
>discomfort.... I really shouldn't eat popcorn... seems the wine turns
>it to concrete :-(
>
>But you do indeed need to watch this space ;-)
>
> ...Jim Thompson
Too much popcorn will lacerate your plumbing. Blood.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
Reply by ●February 4, 20172017-02-04
On Sunday, February 5, 2017 at 2:27:10 AM UTC+11, Jim Thompson wrote:
> On Sat, 4 Feb 2017 01:50:22 -0500, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
> [snip]
> >
> >However, because these models don't correctly represent the internal
> >state of the solutions of the transport equation, a change in conditions
> >is very likely to make the mimicry fail. Sending charge density waves
> >into a 1N914 by hitting it with a step with a big 2-GHz ring is an
> >example. A model based only on the response to a clean step is unlikely
> >to get that right, because it has no way of expressing the wave
> >behaviour, which will have excursions in both density and momentum.
> >
> [snip]
>
> What does the real device do under such circumstances?
>
> Win's post, while at a much lower frequency, would indicate nothing
> visible.
>
> Besides, forward overshoot and reverse recovery are of most importance
> to the power supply application, not something with a "2-GHz ring".
>
> I have 55 "learned" papers on Spice modeling forward overshoot and
> reverse recovery.
>
> Their models are grotesque complex because they aren't Spice
> aficionados, they're equation bangers ;-)
>
> However their models do match the measured behavior quite closely.
>
> But so does mine at 11 lines total... a much simpler approach using
> controlled sources (that allow equations in their templates ;-)
>
> I _will_ ultimately publish. What I seek yet is a way to simply plug
> in numbers from a datasheet and automatically parameterize the model's
> equations. Right now I have to manually twiddle coefficients until I
> get a fit.\
> Of note, once fit, the model behavior _does_ track slew rate _and_
> peak current values.
Working within a restricted parameter space, a model doesn't have to be physically realistic to work. Physically realistic models can be expected to hold up better when used outside the operating range within which the model was fitted.
--
Bill Sloman, Sydney
Reply by Jim Thompson●February 4, 20172017-02-04
On Sat, 4 Feb 2017 16:29:42 -0800 (PST), pcdhobbs@gmail.com wrote:
>>Nothing is impossible to model with Spice.
>>Watch this space >:-}
>
>Wow, between that and the Donald, I may OD on popcorn. ;)
>
>Cheers
>
>Phil Hobbs
I did that last night... and now I am suffering some intestinal
discomfort.... I really shouldn't eat popcorn... seems the wine turns
it to concrete :-(
But you do indeed need to watch this space ;-)
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Thinking outside the box... producing elegant solutions.