The "left" part of the I-V curve with the current load is physically
unrealisable because it requires the rail Vpv400W to go negative.
This can't happen with a resistive load. Try adding the "LOAD"
parameter to the current source. Ideal current sources don't exist
in the real world.
Hi,
I am trying to understand how MPPT works in a buck converter
with resistive load by doing an LTSpice simulation. I have a PV
model which works very accurately with a current sink load. And
it works perfectly as in figure below (I can also change
irradiance and its very accurate with the datasheet)
But
when I use a buck converter with a resistive load I can not
achieve the left part of the IV curve. I am changing the duty
cycle from 0 to 0.98 continuously (kind of) in 0.12s. I cant get
the left part and I think this is logical because with a
resistor at the output load there is no way that voltage will
increase but current stay constant because resistor is a passive
load. As in the figure below
I
added the figures in the folder "MPPT
Resistive Load"?
?
Why
I cant go to the left part of the IV curve ?
Re: How can I create a continuously (kind of) varying duty cycle in one simulation
I am trying to create a duty cycle that kind of continuously
varying like in a 200ms simulation I want a duty cycle start
from 0.01 to 0.99 ?(approximately 0.01 Duty increase per 2 ms).
How can I do this I am really struggling with it .?
Thanks
Trying to understand how MPPT works in a buck converter with resistive load (heating rod)
Hi, I am trying to understand how MPPT works in a buck converter with resistive load by doing an LTSpice simulation. I have a PV model which works very accurately with a current sink load. And it works perfectly as in figure below (I can also change irradiance and its very accurate with the datasheet)
But when I use a buck converter with a resistive load I can not achieve the left part of the IV curve. I am changing the duty cycle from 0 to 0.98 continuously (kind of) in 0.12s. I cant get the left part and I think this is logical because with a resistor at the output load there is no way that voltage will increase but current stay constant because resistor is a passive load. As in the figure below
I added the figures in the folder "MPPT Resistive Load"?
?
Why I cant go to the left part of the IV curve ?
Re: How can I create a continuously (kind of) varying duty cycle in one simulation
I am fairly new to LTspice, so my suggestion may not be the best way to go about implementing what you are looking for. However, can the following trick help you?
I have ended at 8 milliseconds. You will have to go until 199.99m 0.99 199.999m 0.01 endrepeat. This is not an optimal solution but the only way I could come up with.
There's a similar kind of question which is better than what I have suggested.
?
With Regards,
Ankit
Re: How to simulate the gate charge characteristic given in the datasheet of a mosfet?
A very good day to you. Again thanks a lot for explaining the insights on how to use .meas intelligently. I am grateful to you, teacher.
?
I looked at figure 5 of the white paper carefully. You are correct. I was confusing Ton (Toff) with the time period during which Eon (Eoff) need to be calculated. Now I understand the difference clearly.
?
Amidst all the discussion I overlooked some of the key concepts that are essential to these simulations and I can certainly use a second opinion from you.
?
1) Double Pulse Test (DPT) is used for device characterization and estimating these parameters. Am I correct? Links such as , , and evaluated the Eon and Eoff using two pulses, where as in , the evaluation has been done using a single pulse. Your simulation file 2n7002 mosfet Eon also works with a single pulse. Will there be too much of variation in the results between the two approaches?
2) Most semiconductor manufacturers evaluate the performance of the body diode using a DPT. I scrolled through the datasheets of a few didoes (Schottky and Ultrafast Recovery) with ratings 650V, 25A and above. In the datasheets that I looked, I was unable to find a description of the test circuit used to arrive at the results provided in them. I wonder how will the test circuit look like for a diode. Can I use the same circuit as that for a MOSFET, switch it ON and OFF and measure the losses across the diode when it is freewheeling? Will this be a reasonable approach?
3) Does .meas command detect the conditions it is supposed to detect while the simulation is running or after the simulation is over? I am under the assumption that measurement and simulation happen side by side and therefore only known triggers can be detected.
4) Lastly, if the models provided by the manufacturers are well detailed and the simulation has been set up properly will the simulation results be as accurate as the hardware results?
Once again thank you for all the help.
With Regards, Ankit
How can I create a continuously (kind of) varying duty cycle in one simulation
I am trying to create a duty cycle that kind of continuously varying like in a 200ms simulation I want a duty cycle start from 0.01 to 0.99 ?(approximately 0.01 Duty increase per 2 ms). How can I do this I am really struggling with it .?
On Wed, Apr 9, 2025 at 10:42 AM, <gkhebert2@...> wrote:
...? The model designer(s) of the universal opamp seem to have assumed that all opamps have MOS inputs ...
That might be so, but I personally doubt it.? Just my opinion.
...? Opamps with bipolar input devices have substantially lower differential input impedance than common-mode input impedance ...
That might be why these UniversalOpamp models lack any explicit provision for Rin(CM).? It seems to have been ignored - even though its presence is definitely there in these models, even disproportionately there.
?
...? The also have input bias currents, which are missing from all of the universal opamp models.
That might have been intentional, to give you just the basics of a "universal" op-amp without that particular distraction.? Some bipolar op-amps have input bias cancellation, with an average bias current of zero and a spread around it, both positive and negative.? That makes it difficult to represent in a SPICE model.
?
At the time these UniversalOpamp models were made, which I believe would have been 20 or 25+ years ago, bipolars were the first choice.
Weren't these models changed soon after AD
took over?
On 2025-04-09 16:04, Andy I via
groups.io wrote:
It seems as if whoever designed these Universal Opamps gave
no thought whatsoever to a common-mode input impedance.? Not one
of them has a parameter for that.
?
If you ground either input pin and measure the impedance
between the input pins, you get what appears to be an impedance
between the pins of Rin, so you can fool yourself by doing that.
?
I assumed it was Mike Engelhardt who made these models.? I am
guessing he just overlooked this.
?
Andy
?
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
It seems as if whoever designed these Universal Opamps gave no thought whatsoever to a common-mode input impedance.? Not one of them has a parameter for that.
?
If you ground either input pin and measure the impedance between the input pins, you get what appears to be an impedance between the pins of Rin, so you can fool yourself by doing that.
?
I assumed it was Mike Engelhardt who made these models.? I am guessing he just overlooked this.
Far from 'universal', then. These surprising
issues should be fixed, because the errors caused by the present
models could be very serious. Input resistances are often very
important in opamp circuits. It's possible to work round the
absence of bias currents, and it's probably better to do that
than include them in the models.
On 2025-04-09 15:36, gkhebert2 via
groups.io wrote:
I also noticed the input impedance issue some time ago.? The
model designer(s) of the universal opamp seem to have assumed
that all opamps have MOS inputs wherein the input resistance is
determined almost entirely by the impedance of the ESD
protection structures to the supply rails.? Opamps with bipolar
input devices have substantially lower differential input
impedance than common-mode input impedance and this does
manifest as performance differences in different circuit
topologies.? The also have input bias currents, which are
missing from all of the universal opamp models.
--
Best wishes John Woodgate RAYLEIGH Essex OOO-Own Opinions Only
If something is true: * as far as we know - it's science *for
certain - it's mathematics *unquestionably - it's religion
I also noticed the input impedance issue some time ago.? The model designer(s) of the universal opamp seem to have assumed that all opamps have MOS inputs wherein the input resistance is determined almost entirely by the impedance of the ESD protection structures to the supply rails.? Opamps with bipolar input devices have substantially lower differential input impedance than common-mode input impedance and this does manifest as performance differences in different circuit topologies.? The also have input bias currents, which are missing from all of the universal opamp models.
I just tried in another platform, with XVII & V.24, ran the same file using 'AD746', it runs well.
?
I guess, it's because the search paths configuration in V24. I pasted lots paths from XVII's lib paths (including recursive) into V.24's 'searh paths' setting which doesn't support recursive searching.
Then it gives the wrong reference to ...something else. (ADA4830? ADA4857? ...)
The UniversalOpamp model really makes sense, it draws lots current flow.
Since it hurts because of the larger power dissipation, so I give a shot by using local 'AD746', it draws much fewer current, though possibly could be adjusted by external parameters, more efforts needed.
Above ~2.29Hz, the common mode impedance will be larger than differential mode impedance about starting with 9.8G. (Same as gravity value) Apply the common sense rule, common mode impedance should be greater than differential mode.
?
Maybe I don't have the common sense, knowing so much different things all over the world, eg: I haven't noticed the 'common mode > differential mode... things'. But still eager to learn more.
Maybe something is inevitable ,eg: Unfortunately, we can't know/fix every bug, same as the laplace transformation issue mentioned before, see below: That one broken my heart, (sorry correct to ) religion.
All models should play happily, but the simulator platform mechanism always alternate between bright & dark, peak & valley. Sooner or later, unfortunately.
Which , I mean in the file I changed from the UniversalOpamps to AD746, it plays very sadly not going right in new simulator LTspice V.24.1.5 , which I modified it in LTspice XVII V.17.0.37.0, and when migrate it to run in new one , it feedbacks the following message:
Problem fixed ... found out how to make Microsoft Edge open .html files, instead of Notepad, in my Laptop App Settings ... bingo ... I must have set up Notepad as the Default when I was adding 3rd party models to my Spice Libraries.? Another Brick in the Wall.
Re: this Group web site .... I searched the Files, Database and Wiki sections but did not think to look in the Home page .... :(
Re: Analog Devices .... I have searched that site several times and only found this page ?? which is 24.1.6? or LTspice XVII ... :(
That said, I can download 24.0.12 from both sources.
?
I tried the "Repair" option provided in the LTspice download ... no change;? I did an Uninstall and Re-install with the same outcome.??
?
LTspice Help Menu did function on this laptop until recently ..... so my problem must be some File/Program Property(??) that I have selected wittingly or unwittingly ... veeeerrryyyy frustrating that I don't understand this stuff sufficiently to fix it myself ... I will delve into File associations and?html .... gulp.
Tony Casey
John Woodgate