# Waveform simulation in LTspice

Discussion in 'General Electronics Discussion' started by RATAN ROY, Jan 13, 2016.

1. ### RATAN ROY

4
0
Jan 13, 2016
Hi All,
I am trying to generate transient waveform using LTspice exponential voltage source. I am not able achieve the desired waveform. Can anybody help me how to get desired waveform. My desired waveform is as below with T1 = 40 microseconds and T2=120 microseconds. At T2 Voltage amplitude should be 50% of peak voltage amplitude

Thank you so much.

2. ### Alec_t

2,965
804
Jul 7, 2015
Welcome to EP!
Does i/v mean
1) i divided by v
2) i OR v
?
Is the rounded top to the waveform essential, or would a conventional RC charge/discharge waveform do?

Edit: The nearest I could get to the first waveform was by setting the source properties as EXP(0 1 0 40u 40u 80u)

Last edited: Jan 14, 2016
3. ### Harald KappModeratorModerator

11,530
2,656
Nov 17, 2011
Go to our resources -> simulators -> LTSPICe, you'll find useful information there, including surge pulses as shown above.

The latter. This is a typical surge waveform as described in various standards.

The exact waveform is imho not that critical. The relevant point are 100% at T1 and 50% T2 with an exponential decay after T=T1. This waveform is typically generated in a test generator by a combination of RLC elements and switches. It is furthermore coupled to a device under test via coupling networks consisting of RLC eleme´nt themselves. It would be moot to try to synthesize the waveform in more detail, especially considering that the real test more often than not reveals effects that could not be simulated simply because they were unknown at the time of simulation (e.g. stray capacitances from wiring and/or PCB traces).

4. ### LvW

604
146
Apr 12, 2014
The requested transient waveform is a typical step response of a low-Q second-order bandpass.
So - it shouldn`t be a problem to create such a signal.

#### Attached Files:

• ###### Step_response.pdf
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34.9 KB
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Arouse1973 likes this.
5. ### RATAN ROY

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Jan 13, 2016
My thought is also same with you. May be some RLC network needs to be added with appropriate voltage source. Hopefully by changing RLC value we can control T1 & T2 as required. Since I am new in this waveform simulation need your help to generate waveform and perform simulation.

Can we do cable modelling as well in LTspice? Would be appreciated if some reference materials can be provided.

6. ### LvW

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146
Apr 12, 2014
Ratan - didn`t you read my answer? A simple RC-CR bandpass will do the job to transfer a step signal into the desired waveform .
The example provided with my anser is a RC lowpass (1k, 16nF) in series with a CR highpass (16n, 100k).

7. ### RATAN ROY

4
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Jan 13, 2016
I would definitely try with the info you provided. I believe I need to take pulse voltage source with above mentioned elements added in schematic. Thank you so much.

8. ### LvW

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Apr 12, 2014
Of course, you must tune the parts values according to your timing requirements (T1 and T2).

9. ### Harald KappModeratorModerator

11,530
2,656
Nov 17, 2011
The complete description of how to simulate your waveform is in my LTSPICE ressource. Did you even care to look it up as suggested in post #3? You can directly set the peak voltage and the timing parameters.

10. ### RATAN ROY

4
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Jan 13, 2016
I have tried to generate same waveform here. Played around with component value to achieve desired T1 (40us) and T2 (120us). T2 needs to be considered at 50% of peak amplitude. It sounds I achieved T1 but not T2 yet. One more thing I observed is peak amplitude is significantly reduced 600V to 357V. The max I got T2 at 50% of peak amplitude is about 89us.

Here I attached my experimental schematics. Look forward for your help. I would be glad if you can provide some references on cable modeling in LTspice that would be great. I want to study that too.