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Step a resistor over time

 

Hi All, is it possible to step a resistor over time? Right now if I use the step command like this:

.step param R 100 1000 100
.tran 0 1ms 0 1

I
end up with a bunch of parallel horizontal lines. What I want is a
bunch of points (maybe even connected) over time. So in other words,
over the 1ms, I want the resistance to step from 100 to 1000. Is it
possible?

Thanks!
Richard
 

--- In LTspice@..., Richard Norman <rnorman3@...> wrote:

Hi All, is it possible to step a resistor over time? Right now if I use the step command like this:

.step param R 100 1000 100
.tran 0 1ms 0 1

I
end up with a bunch of parallel horizontal lines. What I want is a
bunch of points (maybe even connected) over time. So in other words,
over the 1ms, I want the resistance to step from 100 to 1000. Is it
possible?

Thanks!
Richard

Hello Richard,

You can use formulas instead of a fixed value for a resistor.
Therefore replace the value of 1k on your resistor with a
formula. See below.

R=100*(1+time/10m)

This will rise the resistance from 100Ohm to 1kOhm in 90ms.

Best regards,
Helmut
 

Hi Richard,
?
Aside from the form Helmut gave you, you can set any resistor to as many changes as you need. The format, which is entered in the resistance window in place of a single value is :
???
???? R=table(time,0,res1,time1a,res1,time1b,res2.....,last res)
?
Example : R=table(time,0,10K,3m,10K,3.00001m,100K,6m,100K,6.00001m,1)
?
This starts with the resistance value at 10K until 3mS after start, then steps to 100K until 6mS and then to 1 ohm for the rest of the run. The run duration sets the max time end point. Careful to place comma's between each entry, and no spaces.
?
If you want a slope change instead of a step, for example a changing value of 100 ohms to 10 ohms over a 10mS time and back to 100 ohms over the next 10mS,?the form would be:
?
???? R=table(time,0,100,10m,10,20m,100)
?
Lastly, always check your entries for pairs. There must be a time/value pair for each entry. This listing approach is invaluable for all sorts of applications which require either a slope or step change such as load testing etc.
?
- Cordially - RC
?


________________________________
From: Richard Norman <rnorman3@...>
To: "ltspice@..." <ltspice@...>
Sent: Sunday, April 14, 2013 2:30 AM
Subject: [LTspice] Step a resistor over time

?

Hi All, is it possible to step a resistor over time? Right now if I use the step command like this:

.step param R 100 1000 100
.tran 0 1ms 0 1

I
end up with a bunch of parallel horizontal lines. What I want is a
bunch of points (maybe even connected) over time. So in other words,
over the 1ms, I want the resistance to step from 100 to 1000. Is it
possible?

Thanks!
Richard

[Non-text portions of this message have been removed]




[Non-text portions of this message have been removed]
 

Hi Ron,
Thanks for sharing the inline table approach - very useful too! But I can't seem to see what differentiates the step version from the slope version. Can you elaborate please?
Thanks,
Mike

--- In LTspice@..., Ron Liff <ron_liff@...> wrote:

Hi Richard,
??
Aside from the form Helmut gave you, you can set any resistor to as many changes as you need. The format, which is entered in the resistance window in place of a single value is :
??????
???????? R=table(time,0,res1,time1a,res1,time1b,res2.....,last res)
??
Example : R=table(time,0,10K,3m,10K,3.00001m,100K,6m,100K,6.00001m,1)
??
This starts with the resistance value at 10K until 3mS after start, then steps to 100K until 6mS and then to 1 ohm for the rest of the run. The run duration sets the max time end point. Careful to place comma's between each entry, and no spaces.
??
If you want a slope change instead of a step, for example a changing value of 100 ohms to 10 ohms over a 10mS time and back to 100 ohms over the next 10mS,??the form would be:
??
???????? R=table(time,0,100,10m,10,20m,100)
??
Lastly, always check your entries for pairs. There must be a time/value pair for each entry. This listing approach is invaluable for all sorts of applications which require either a slope or step change such as load testing etc.
??
- Cordially - RC
??


________________________________
From: Richard Norman <rnorman3@...>
To: "ltspice@..." <ltspice@...>
Sent: Sunday, April 14, 2013 2:30 AM
Subject: [LTspice] Step a resistor over time

??

Hi All, is it possible to step a resistor over time? Right now if I use the step command like this:

.step param R 100 1000 100
.tran 0 1ms 0 1

I
end up with a bunch of parallel horizontal lines. What I want is a
bunch of points (maybe even connected) over time. So in other words,
over the 1ms, I want the resistance to step from 100 to 1000. Is it
possible?

Thanks!
Richard

[Non-text portions of this message have been removed]




[Non-text portions of this message have been removed]
 

But I can't seem to see what differentiates the step version from the slope version.
The difference is the shape of the curves. They are both PWL
(piecewise linear). The step one changes in steps, abruptly, followed
by periods where the resistance stays fixed. The slope one changes
like a triangular wave. Plot out the values to see for yourself.

Andy
 

Hi Andy,
Thanks for your response, but I do understand step vs slope. My question was actually about some difference in the syntax of the statement examples (which I couldn't detect). For some reason I was thinking that some subtle difference was making the first example actually step. But after closer inspection, I see that they both change in slopes, but the chosen values just force the slopes to be short. Sometimes I miss the obvious...

Thanks,
Mike

--- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:

But I can't seem to see what differentiates the step version from the slope version.
The difference is the shape of the curves. They are both PWL
(piecewise linear). The step one changes in steps, abruptly, followed
by periods where the resistance stays fixed. The slope one changes
like a triangular wave. Plot out the values to see for yourself.

Andy

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