Forums

LT spice, leakage inductance

Started by John Larkin July 20, 2017

I'm simulating a flyback switcher and noticed that any K < 1 in the
transformer radically slows down the sim, which is annoyingly slow
already... 90 seconds to sim 60 ms of startup and a little pulsed load
blip. Maybe 6:1 slower with a little leakage inductance. So I only
include leakage inductance to tweak the snubber.



-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

On Thu, 20 Jul 2017 11:39:25 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

> > >I'm simulating a flyback switcher and noticed that any K < 1 in the >transformer radically slows down the sim, which is annoyingly slow >already... 90 seconds to sim 60 ms of startup and a little pulsed load >blip. Maybe 6:1 slower with a little leakage inductance. So I only >include leakage inductance to tweak the snubber.
You have to use Mikey's idealized components... fast, but... ...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 | I'm looking for work... see my website. Thinking outside the box...producing elegant & economic solutions.
On 2017-07-20 11:39, John Larkin wrote:
> > > I'm simulating a flyback switcher and noticed that any K < 1 in the > transformer radically slows down the sim, which is annoyingly slow > already... 90 seconds to sim 60 ms of startup and a little pulsed load > blip. Maybe 6:1 slower with a little leakage inductance. So I only > include leakage inductance to tweak the snubber. >
That's probably what we all do. Leakage only on a cycle-by-cycle basis but not for a whole load change reaction run. Besides, it would cause global warming :-) Ever since I bought a PC with an Intel i7 in there things have greatly accelerated in SPICE. -- Regards, Joerg http://www.analogconsultants.com/
On Thu, 20 Jul 2017 12:05:52 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Thu, 20 Jul 2017 11:39:25 -0700, John Larkin ><jjlarkin@highland_snip_technology.com> wrote: > >> >> >>I'm simulating a flyback switcher and noticed that any K < 1 in the >>transformer radically slows down the sim, which is annoyingly slow >>already... 90 seconds to sim 60 ms of startup and a little pulsed load >>blip. Maybe 6:1 slower with a little leakage inductance. So I only >>include leakage inductance to tweak the snubber. > >You have to use Mikey's idealized components... fast, but... > > ...Jim Thompson
Using a discrete inductor to simulate the leakage inductance is no faster. Nice try, JL. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thu, 20 Jul 2017 12:14:06 -0700, Joerg <news@analogconsultants.com>
wrote:

>On 2017-07-20 11:39, John Larkin wrote: >> >> >> I'm simulating a flyback switcher and noticed that any K < 1 in the >> transformer radically slows down the sim, which is annoyingly slow >> already... 90 seconds to sim 60 ms of startup and a little pulsed load >> blip. Maybe 6:1 slower with a little leakage inductance. So I only >> include leakage inductance to tweak the snubber. >> > >That's probably what we all do. Leakage only on a cycle-by-cycle basis >but not for a whole load change reaction run. Besides, it would cause >global warming :-) > >Ever since I bought a PC with an Intel i7 in there things have greatly >accelerated in SPICE.
So we simulate more complex stuff and give all that saved time back. I've got a radically weird PLL that would probably Spice in 1 PPB of real time. We may sim it in Python, or just build it and tweak. Actually, PowerBasic would be better than Python. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thu, 20 Jul 2017 12:26:42 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>On Thu, 20 Jul 2017 12:05:52 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Thu, 20 Jul 2017 11:39:25 -0700, John Larkin >><jjlarkin@highland_snip_technology.com> wrote: >> >>> >>> >>>I'm simulating a flyback switcher and noticed that any K < 1 in the >>>transformer radically slows down the sim, which is annoyingly slow >>>already... 90 seconds to sim 60 ms of startup and a little pulsed load >>>blip. Maybe 6:1 slower with a little leakage inductance. So I only >>>include leakage inductance to tweak the snubber. >> >>You have to use Mikey's idealized components... fast, but... >> >> ...Jim Thompson > >Using a discrete inductor to simulate the leakage inductance is no >faster. Nice try, JL.
What happened to LTspice's "fastest simulator ever" ?>:-} ...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 | I'm looking for work... see my website. Thinking outside the box...producing elegant & economic solutions.
On 2017-07-20 12:31, John Larkin wrote:
> On Thu, 20 Jul 2017 12:14:06 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2017-07-20 11:39, John Larkin wrote: >>> >>> >>> I'm simulating a flyback switcher and noticed that any K < 1 in the >>> transformer radically slows down the sim, which is annoyingly slow >>> already... 90 seconds to sim 60 ms of startup and a little pulsed load >>> blip. Maybe 6:1 slower with a little leakage inductance. So I only >>> include leakage inductance to tweak the snubber. >>> >> >> That's probably what we all do. Leakage only on a cycle-by-cycle basis >> but not for a whole load change reaction run. Besides, it would cause >> global warming :-) >> >> Ever since I bought a PC with an Intel i7 in there things have greatly >> accelerated in SPICE. > > So we simulate more complex stuff and give all that saved time back. >
Not really. I try to be frugal with resources. It's just that for whatever reason I get to design switch-mode converters all the time and those are sim-hungry. So now the job goes faster. I don't particularly enjoy it but it seems hardly anyone else wants to design switchers these days.
> I've got a radically weird PLL that would probably Spice in 1 PPB of > real time. We may sim it in Python, or just build it and tweak. > > Actually, PowerBasic would be better than Python. >
For analog SPICE always rules, except where it doesn't and then it means bench time, soldering iron, coffee or maybe a Pale Ale. It can help to change precision parameters such as RELTOL in SPICE for a faster run but I rarely do that. That was different in the days when all I had was a 80386 running a 25MHz and a Cyrix Math processor. -- Regards, Joerg http://www.analogconsultants.com/
On Thu, 20 Jul 2017 13:02:23 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On Thu, 20 Jul 2017 12:26:42 -0700, John Larkin ><jjlarkin@highland_snip_technology.com> wrote: > >>On Thu, 20 Jul 2017 12:05:52 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >>>On Thu, 20 Jul 2017 11:39:25 -0700, John Larkin >>><jjlarkin@highland_snip_technology.com> wrote: >>> >>>> >>>> >>>>I'm simulating a flyback switcher and noticed that any K < 1 in the >>>>transformer radically slows down the sim, which is annoyingly slow >>>>already... 90 seconds to sim 60 ms of startup and a little pulsed load >>>>blip. Maybe 6:1 slower with a little leakage inductance. So I only >>>>include leakage inductance to tweak the snubber. >>> >>>You have to use Mikey's idealized components... fast, but... >>> >>> ...Jim Thompson >> >>Using a discrete inductor to simulate the leakage inductance is no >>faster. Nice try, JL. > >What happened to LTspice's "fastest simulator ever" ?>:-} > > ...Jim Thompson
I have no idea how fast this would run in some other simulator, or if the leakage L would matter as much. But since I'm using an LTC3803, probably no other software would work. It is a nice chip, the 3803. At around a minute per run, it's not too terrible to iterate the compensation and such. 6 minutes was a bit much. I'm making a DAC-programmable flyback supply, 0 to +70 volts out, a few watts. Gotta pervert the usual feedback scheme. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thu, 20 Jul 2017 14:25:43 -0700, Joerg <news@analogconsultants.com>
wrote:

[snip]
> >For analog SPICE always rules, except where it doesn't and then it means >bench time, soldering iron, coffee or maybe a Pale Ale. > >It can help to change precision parameters such as RELTOL in SPICE for a >faster run but I rarely do that. That was different in the days when all >I had was a 80386 running a 25MHz and a Cyrix Math processor.
386/387, now those were the good old days... start a simulation and check back tomorrow about lunch time ;-) RELTOL _usually_ is _not_ the option to tweak. Instead... Be sure to set "Step gmin" vntol doesn't need to be 1uV, 100uV is fine, or even 1mV for switchers abstol at 1nA is usually quite sufficient nominal gmin=1n is also adequate ...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 | I'm looking for work... see my website. Thinking outside the box...producing elegant & economic solutions.
On Thu, 20 Jul 2017 14:31:49 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

>On Thu, 20 Jul 2017 13:02:23 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Thu, 20 Jul 2017 12:26:42 -0700, John Larkin >><jjlarkin@highland_snip_technology.com> wrote: >> >>>On Thu, 20 Jul 2017 12:05:52 -0700, Jim Thompson >>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>> >>>>On Thu, 20 Jul 2017 11:39:25 -0700, John Larkin >>>><jjlarkin@highland_snip_technology.com> wrote: >>>> >>>>> >>>>> >>>>>I'm simulating a flyback switcher and noticed that any K < 1 in the >>>>>transformer radically slows down the sim, which is annoyingly slow >>>>>already... 90 seconds to sim 60 ms of startup and a little pulsed load >>>>>blip. Maybe 6:1 slower with a little leakage inductance. So I only >>>>>include leakage inductance to tweak the snubber. >>>> >>>>You have to use Mikey's idealized components... fast, but... >>>> >>>> ...Jim Thompson >>> >>>Using a discrete inductor to simulate the leakage inductance is no >>>faster. Nice try, JL. >> >>What happened to LTspice's "fastest simulator ever" ?>:-} >> >> ...Jim Thompson > >I have no idea how fast this would run in some other simulator, or if >the leakage L would matter as much. But since I'm using an LTC3803, >probably no other software would work.
That's the problem with LT, and Analog Devices and sometime TI... if your model will run on only your proprietary simulator, what the f**k good is it?
> >It is a nice chip, the 3803. At around a minute per run, it's not too >terrible to iterate the compensation and such. 6 minutes was a bit >much. > >I'm making a DAC-programmable flyback supply, 0 to +70 volts out, a >few watts. Gotta pervert the usual feedback scheme.
...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 | I'm looking for work... see my website. Thinking outside the box...producing elegant & economic solutions.