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Vin vs. Load - YX logarithmic plot

 

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Hello, I would like to create a simulation of overcurrent protection circuit — a graph where the Y-axis shows the current drop (in Amperes), and the X-axis shows a linear increase of voltage in the range of 15–50 V.

I expect a logarithmic curve of the current decreasing from 1.2 A down to 0 A as the voltage increases. I used the .step param function (.step param Vin 12 50 1), but that’s not what I’m looking for.

?

How should I define such a graph?

?

Thanks Jurek
 

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On 27/04/2025 22:26, jerzy przezdziecki via groups.io wrote:

Hello, I would like to create a simulation of overcurrent protection circuit — a graph where the Y-axis shows the current drop (in Amperes), and the X-axis shows a linear increase of voltage in the range of 15–50 V.

I expect a logarithmic curve of the current decreasing from 1.2 A down to 0 A as the voltage increases. I used the .step param function (.step param Vin 12 50 1), but that’s not what I’m looking for.

?

How should I define such a graph?

If you want a graph of an over-current protection circuit, what does it matter what Vin is? Surely what you're interested in is Iout vs. Vout?

--
Regards,
Tony
 

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Jurek, are you looking for something like a solar panel I/V curve?

Maybe look at the SA Sim.zip I just uploaded.

?

Dave

?

From: [email protected] <[email protected]> On Behalf Of jerzy przezdziecki via groups.io
Sent: Sunday, April 27, 2025 1:27 PM
To: [email protected]
Subject: EXTERNAL: [LTspice] Vin vs. Load - YX logarithmic plot

?

Hello, I would like to create a simulation of overcurrent protection circuit — a graph where the Y-axis shows the current drop (in Amperes), and the X-axis shows a linear increase of voltage in the range of 15–50 V.

I expect a logarithmic curve of the current decreasing from 1.2 A down to 0 A as the voltage increases. I used the .step param function (.step param Vin 12 50 1), but that’s not what I’m looking for.

?

How should I define such a graph?

?

Thanks Jurek
 

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Thanks a lot Dave, it looks exactly like what I need.

?

J

?

From: <[email protected]> on behalf of "Bell, Dave via groups.io" <Dave.Bell@...>
Reply to: <[email protected]>
Date: Sunday, 27 April 2025 at 23:34
To: "[email protected]" <[email protected]>
Subject: Re: [LTspice] Vin vs. Load - YX logarithmic plot
Resent from: <Dave.Bell@...>
Resent date: Sun, 27 Apr 2025 14:34:08 -0700

?

Jurek, are you looking for something like a solar panel I/V curve?

Maybe look at the SA Sim.zip I just uploaded.

?

Dave

?

From: [email protected] <[email protected]> On Behalf Of jerzy przezdziecki via groups.io
Sent: Sunday, April 27, 2025 1:27 PM
To: [email protected]
Subject: EXTERNAL: [LTspice] Vin vs. Load - YX logarithmic plot

?

Hello, I would like to create a simulation of overcurrent protection circuit — a graph where the Y-axis shows the current drop (in Amperes), and the X-axis shows a linear increase of voltage in the range of 15–50 V.

I expect a logarithmic curve of the current decreasing from 1.2 A down to 0 A as the voltage increases. I used the .step param function (.step param Vin 12 50 1), but that’s not what I’m looking for.

?

How should I define such a graph?

?

Thanks Jurek
 

The plot window will give you the chance to scale the axes logarithmically.? Be careful that your results don't include negative or zero values, which will prevent you from selecting log scaling.? At least it works that way in Excel.? In the plot window, hover the mouse over the axis of interest, <RMB> opens the Axis limit window, check the Logarithmic box at the bottom.??
I apologize if this is obvious to you.? I get frustrated with some answers that assume I know the intricacies of a program I'm still trying to learn.
?
 

... and I don't read ahead and see the question has already been answered.? DOH!
 

You can change to a logarithmic axis (in LTspice) even if the waveform has negative values.? It just won't plot over those ranges.? Best to add a limiting function first (in the waveform window).
?
LTspice is a wonderful learning experience.? There tends to be more than you knew, just waiting for you to try.
?
Andy
 

On Fri, May 2, 2025 at 10:30 AM, <rick_church@...> wrote:
The plot window will give you the chance to scale the axes logarithmically.? ...
I want to add this note:? Usually when I change the Y-axis from linear to log, LTspice scales the Y-axis so that it?covers too much range (too many decades), making it a less useful plot.? If I immediately right-click in the plot pane and select "Autorange Y-axis", it usually fixes that problem.
?
If the Y-axis waveform includes negative values, then it might still be scaled with too much range to be helpful.? In that case, right-click on the Y-axis and set a new value for the Bottom, so that the displayed plot does not cover so wide a range.
?
Andy
?
 

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“If I immediately right-click in the plot pane and select "Autorange Y-axis", it usually fixes that problem”

Begging the question of why that *颈蝉苍’迟* the Automatic default!

?

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Friday, May 02, 2025 10:51 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Vin vs. Load - YX logarithmic plot

?

On Fri, May 2, 2025 at 10:30 AM, <rick_church@...> wrote:

The plot window will give you the chance to scale the axes logarithmically.? ...

I want to add this note:? Usually when I change the Y-axis from linear to log, LTspice scales the Y-axis so that it?covers too much range (too many decades), making it a less useful plot.? If I immediately right-click in the plot pane and select "Autorange Y-axis", it usually fixes that problem.

?

If the Y-axis waveform includes negative values, then it might still be scaled with too much range to be helpful.? In that case, right-click on the Y-axis and set a new value for the Bottom, so that the displayed plot does not cover so wide a range.

?

Andy

?
 

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I find that in many cases, the plotted variable does reach very small values, which are of no significance or interest, but Autorange accommodates them, as it should, having no 'knowledge' of which values are significant. The same occasionally applies to initial very large values, such as inrush current.

On 2025-05-02 21:18, Bell, Dave via groups.io wrote:

“If I immediately right-click in the plot pane and select "Autorange Y-axis", it usually fixes that problem”

Begging the question of why that *颈蝉苍’迟* the Automatic default!

?

?

From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Friday, May 02, 2025 10:51 AM
To: [email protected]
Subject: EXTERNAL: Re: [LTspice] Vin vs. Load - YX logarithmic plot

?

On Fri, May 2, 2025 at 10:30 AM, <rick_church@...> wrote:

The plot window will give you the chance to scale the axes logarithmically.? ...

I want to add this note:? Usually when I change the Y-axis from linear to log, LTspice scales the Y-axis so that it?covers too much range (too many decades), making it a less useful plot.? If I immediately right-click in the plot pane and select "Autorange Y-axis", it usually fixes that problem.

?

If the Y-axis waveform includes negative values, then it might still be scaled with too much range to be helpful.? In that case, right-click on the Y-axis and set a new value for the Bottom, so that the displayed plot does not cover so wide a range.

?

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

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