EDAboard.com | EDAboard.de | EDAboard.co.uk | WTWH Media

weird LT Spice

Ask a question - edaboard.com

elektroda.net NewsGroups Forum Index - Electronics Design - weird LT Spice

Goto page 1, 2  Next

John Larkin
Guest

Thu Feb 07, 2019 12:45 am   



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
http://www.highlandtechnology.com

Martin Riddle
Guest

Thu Feb 07, 2019 2:45 am   



On Wed, 06 Feb 2019 15:34:22 -0800, John Larkin
<jjlarkin_at_highland_snip_technology.com> wrote:

Quote:


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.


What did you expect for FREE ?

Cheers

John Larkin
Guest

Thu Feb 07, 2019 3:45 am   



On Wed, 06 Feb 2019 20:40:27 -0500, Martin Riddle
<martin_ridd_at_verizon.net> wrote:

Quote:
On Wed, 06 Feb 2019 15:34:22 -0800, John Larkin
jjlarkin_at_highland_snip_technology.com> wrote:



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.

What did you expect for FREE ?

Cheers


Heck, expensive software is buggy too. I prefer free bugs!

The 1V supply fixed it, but adding a diode broke it again.

Setting the transient response option "skip initial operating point
solution" is ugly but does fix it.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

Clive Arthur
Guest

Thu Feb 07, 2019 12:45 pm   



On 06/02/2019 23:34, John Larkin wrote:
Quote:


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.



I've had a few weird things happen which get fixed after saving, closing
and restarting. I think LTspice XVII is buggier than the older
versions, but still very good value.

Cheers
--
Clive


Guest

Thu Feb 07, 2019 1:45 pm   



On Thursday, February 7, 2019 at 1:13:21 PM UTC+11, John Larkin wrote:
Quote:
On Wed, 06 Feb 2019 20:40:27 -0500, Martin Riddle
martin_ridd_at_verizon.net> wrote:

On Wed, 06 Feb 2019 15:34:22 -0800, John Larkin
jjlarkin_at_highland_snip_technology.com> wrote:



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.

What did you expect for FREE ?

Cheers

Heck, expensive software is buggy too. I prefer free bugs!

The 1V supply fixed it, but adding a diode broke it again.

Setting the transient response option "skip initial operating point
solution" is ugly but does fix it.


One should never underestimate one's capablity for screwing up a simulation by hitting the wrong key or selecting the wrong option.

That kind of error can be very hard to find, and excruciatingly embarrassing when you do find it, or somebody else finds it for you (which is usually the quickest option, if you can survive looking like an idiot).

--
Bill Sloman, Sydney

boB
Guest

Thu Feb 07, 2019 5:45 pm   



On Thu, 7 Feb 2019 11:28:54 +0000, Clive Arthur
<cliveta_at_nowaytoday.co.uk> wrote:

Quote:
On 06/02/2019 23:34, John Larkin wrote:


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.



I've had a few weird things happen which get fixed after saving, closing
and restarting. I think LTspice XVII is buggier than the older
versions, but still very good value.

Cheers


I have seen LTspice circuits not converge until I added something
weird, for example, I got it to work once by adding just ONE end of a
resistor to the circuit. Later versions did not need it.

Also, sometimes you need to add a high value (several MegOhms)
resistor from a floating node to a grounded node to get it to
converge.

But your circuit converges right ? It just comes up with a blank
trace ? That I haven't seen before as far as I remember.

I will assume that future versions of LTspice won't require that weird
battery connection.


Guest

Thu Feb 07, 2019 5:45 pm   



On Wednesday, February 6, 2019 at 6:34:30 PM UTC-5, John Larkin wrote:
Quote:
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.


You have GND missing somewhere whether it's used in the actual circuit or not, you need to rig it. Probe needs a reference.


Quote:



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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


John Larkin
Guest

Thu Feb 07, 2019 6:45 pm   



On Thu, 7 Feb 2019 08:36:55 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

Quote:
On Wednesday, February 6, 2019 at 6:34:30 PM UTC-5, John Larkin wrote:
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.

You have GND missing somewhere whether it's used in the actual circuit or not, you need to rig it. Probe needs a reference.



The circuit is fairly simple and visually correct. It does use some
EPC GaN fets, with an included library, but I've used that many times
before and the .lib file looks OK.

Spice doesn't complain about convergence or take long to run the sim.
It's just as though all nodes except the single pulse generator simply
don't exist, and don't show a plot line if probed. Not even the +12
volt power supply.

And it's erratic; adding a part might fix it or break it.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Gerhard Hoffmann
Guest

Thu Feb 07, 2019 6:45 pm   



Am 07.02.19 um 17:31 schrieb boB:

Quote:
I have seen LTspice circuits not converge until I added something
weird, for example, I got it to work once by adding just ONE end of a
resistor to the circuit. Later versions did not need it.

Also, sometimes you need to add a high value (several MegOhms)
resistor from a floating node to a grounded node to get it to
converge.


There is no such thing as a floating node in Spice. Everything
has to have some connection to node 0 (gnd). The first thing
that spice does to your circuit is constructing a conductance
matrix and zero or not-completely-0-but-nearly entries mess up
the algorithms that follow. Just imagine computing a voltage
difference between 2 nodes from current and NO conductance. i/0.

To avoid that, Spice normally adds huge resistors to nodes that
are not connected "enough". The size of these resistors is hard
to determine. Make them too large and the equation system will
not converge, make them too small and the user will complain
that the results are not accurate. And resistances/conductance
may change wildly during simulation.

So you don't add just one end of a resistor to the circuit.
The other end is connected also via the invisible large R.

And WRT LTspice support: If you feed your problem into the
provided channels, it will be fixed pretty soon. Last week I
heard of a case where writing sound files did not work for
resolutions other than 16 bits. That was fixed within hours.

regards,
Gerhard

John S
Guest

Fri Feb 08, 2019 2:45 pm   



On 2/6/2019 5:34 PM, John Larkin wrote:
Quote:


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.


Which version? If it is XVII, that may be the problem. Try it with
version IV.


Guest

Fri Feb 08, 2019 5:45 pm   



On Wednesday, February 6, 2019 at 9:13:21 PM UTC-5, John Larkin wrote:
Quote:
On Wed, 06 Feb 2019 20:40:27 -0500, Martin Riddle
martin_ridd_at_verizon.net> wrote:

On Wed, 06 Feb 2019 15:34:22 -0800, John Larkin
jjlarkin_at_highland_snip_technology.com> wrote:



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.

What did you expect for FREE ?

Cheers

Heck, expensive software is buggy too. I prefer free bugs!

The 1V supply fixed it, but adding a diode broke it again.

Setting the transient response option "skip initial operating point
solution" is ugly but does fix it.


Check to see if you have an undriven node lurking somewhere. Spice doesn't like those and may or may not throw a fit.

Rick C.


Guest

Fri Feb 08, 2019 5:45 pm   



On Thursday, February 7, 2019 at 12:01:21 PM UTC-5, John Larkin wrote:
Quote:
On Thu, 7 Feb 2019 08:36:55 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Wednesday, February 6, 2019 at 6:34:30 PM UTC-5, John Larkin wrote:
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.

You have GND missing somewhere whether it's used in the actual circuit or not, you need to rig it. Probe needs a reference.



The circuit is fairly simple and visually correct. It does use some
EPC GaN fets, with an included library, but I've used that many times
before and the .lib file looks OK.

Spice doesn't complain about convergence or take long to run the sim.
It's just as though all nodes except the single pulse generator simply
don't exist, and don't show a plot line if probed. Not even the +12
volt power supply.

And it's erratic; adding a part might fix it or break it.


Does it even work at DC? That's usually easiest to debug. It's probably your fet models.

Quote:


--

John Larkin Highland Technology, Inc

lunatic fringe electronics


Piotr Wyderski
Guest

Fri Feb 08, 2019 5:45 pm   



John Larkin wrote:

> That's weird.

The LTSpice UI is not particularly well-known for its quality.
I hate when it ignores manually changed .param values and sticks to the
old ones. Only one change per 3 or 4 take the desired effect. The way
it looks like on a 4k display is another "feature"...

Best regards, Piotr

John Larkin
Guest

Fri Feb 08, 2019 5:45 pm   



On Fri, 8 Feb 2019 07:15:36 -0600, John S <Sophi.2_at_invalid.org> wrote:

Quote:
On 2/6/2019 5:34 PM, John Larkin wrote:


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.


Which version? If it is XVII, that may be the problem. Try it with
version IV.


XVII, which is otherwise pretty good. IV isn't supported any more.

I think the problem is that I have some optional peaking inductors in
series with some fet gates. If I set the values small, around expected
circuit parasitics, the equivalent time constants or resonant
frequencies get crazy and the initial conditions solution doesn't
converge. But there is no warning, the sim runs, and the symptom
becomes this invisible node thing.

Removing the inductors, or skipping the initial condition solution,
either one fixes it.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

John Larkin
Guest

Fri Feb 08, 2019 6:45 pm   



On Fri, 8 Feb 2019 08:34:54 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

Quote:
On Thursday, February 7, 2019 at 12:01:21 PM UTC-5, John Larkin wrote:
On Thu, 7 Feb 2019 08:36:55 -0800 (PST),
bloggs.fredbloggs.fred_at_gmail.com wrote:

On Wednesday, February 6, 2019 at 6:34:30 PM UTC-5, John Larkin wrote:
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.

You have GND missing somewhere whether it's used in the actual circuit or not, you need to rig it. Probe needs a reference.



The circuit is fairly simple and visually correct. It does use some
EPC GaN fets, with an included library, but I've used that many times
before and the .lib file looks OK.

Spice doesn't complain about convergence or take long to run the sim.
It's just as though all nodes except the single pulse generator simply
don't exist, and don't show a plot line if probed. Not even the +12
volt power supply.

And it's erratic; adding a part might fix it or break it.

Does it even work at DC? That's usually easiest to debug. It's probably your fet models.


A grounded +1V DC power supply, connected to nothing in the circuit,
probes as "no line."

I should look at the .RAW file. Probably mostly empty.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Goto page 1, 2  Next

elektroda.net NewsGroups Forum Index - Electronics Design - weird LT Spice

Ask a question - edaboard.com

Arabic version Bulgarian version Catalan version Czech version Danish version German version Greek version English version Spanish version Finnish version French version Hindi version Croatian version Indonesian version Italian version Hebrew version Japanese version Korean version Lithuanian version Latvian version Dutch version Norwegian version Polish version Portuguese version Romanian version Russian version Slovak version Slovenian version Serbian version Swedish version Tagalog version Ukrainian version Vietnamese version Chinese version Turkish version
EDAboard.com map