Understanding Multisim Simulation Results: Schematic and Oscilloscope Analysis

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Discussion Overview

The discussion revolves around the interpretation of simulation results from Multisim, specifically regarding the behavior of a transformer circuit with capacitors and switches. Participants explore the discrepancies between simulated and real-world behavior, focusing on oscillation patterns, transformer functionality, and the implications of using DC in simulations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion over the simulation results, noting that the oscilloscope displays a square wave despite the capacitors being partially charged, which should theoretically affect the current and transformer flux.
  • Another participant suggests that the model used by Multisim may not accurately represent a real transformer, particularly in its behavior with DC.
  • A participant questions the utility of the circuit design, indicating that if the capacitors charge, the transformer may cease to function effectively.
  • It is noted that removing the capacitors still yields similar results in the simulation, raising questions about the nature of the transformer model in Multisim.
  • One participant posits that the observed voltage readings on the oscilloscope contradict the expected behavior of a transformer when there are no oscillations in the primary circuit.
  • Another participant explains that ideal transformers can operate with both AC and DC in theory, but this may not reflect practical applications.
  • There is a discussion about the phase shift of current in relation to different waveforms, with one participant questioning how to address phase shifts when the input is not a sine wave.
  • A suggestion is made to study DC/DC converters and a specific resource is recommended for further understanding of inductors.

Areas of Agreement / Disagreement

Participants express varying opinions on the validity of the Multisim transformer model and its implications for real-world applications. There is no consensus on the effectiveness of the circuit design or the interpretation of the simulation results.

Contextual Notes

Participants highlight limitations in understanding the behavior of transformers under DC conditions and the assumptions made in the simulation model. The discussion reflects uncertainty about the implications of capacitor charge on transformer operation.

Crazymechanic
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Hi once again I don't really understand multisim simulated results as i find them kinda not 1:1 with reality, I am not sure maybe someone here can help.
In this schematic a switch the switches one one at a time.
For the first time when each of the switches is switched on each of the caps charge.While they charge a current runs through them which also runs through the primary winding.
When I continue switching the caps still maintain some if not most of their charge , so how come the oscilloscope show a clear square wave when switching as each next time because the capacitor is already atleast half charged the current rush towards it is far less than if it were empty so the flux in the transformer should change too and the reading on the oscilloscope too.
Well check it out for yourselves.

I zipped the ms. file because somebody has made it impossible to attach a multisim file directly.Kinda stupid.
 

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Please add diagram in PNG format, everybody don't have to use multisim.
 
here you are:)
 

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What are you try to achieve ? With this strange circuit?
Have you check what type of a model multisime is using to model the behavior of the transformer?
Maybe this "model" also work with DC and don't behaves just like a real transformer. Have you checked this?
 
Last edited:
No I haven't , the circuit is thought to produce a back and forth oscillations so that the transformer could work.
Ofcourse it is only useful until /if the capacitors stay empty, if they charge up hen no charge flows any more so no change in the em field and the transformer stops doing it's job.
so the question rather is does this can work , including the back emf etc etc , guess rather not, and secondly what is a dc transformer , as transformers don't work on dc ?
 
Real transformers don't work on DC but in multimsime they work on DC also.
Simply remove capacitors from your circuit and see if we get the same result.
 
yes we get the same result, also what made me wonder is that when I leave one switch closed and the other opened , the oscilloscope reads either + or - 50 volts from the secondary , but normally that couldn't happen because as if there are no oscillations anymore in the primary there should be no induction in secondary.
So I guess multisim uses somekind of a weird dc transformer , I can't understand the reason one would need that as if it doesn't work in real life.

what do you think if both sides of the primary are equally loaded should there be any current on the switches , if a high frequency is used , and no capacitors ? Theoretically there should but doesn't the back EMF stop it if the switches are cut off before the flux in the core reaches it's peak 90 degrees after voltage is applied?
 
So I guess multisim uses somekind of a weird dc transformer , I can't understand the reason one would need that as if it doesn't work in real life.
We use this "weird transformer" to model basic principal of how ideal transformer work.
Transformer can step up/down voltages and Pin = Pout nothing more. An ideal transformer is a perfect transformer of both AC and DC.

In general flux in the core the integral of the applied voltage waveform. So only for a sin wave voltage, the flux in the core lags 90 degrees after voltage is applied. Because if you integral sin wave you will get a cosine wave.
 
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Ok so then by how many degrees the current lags a say , square wave , even though there is no true square wave , especially in circuit parts that have inductance like a inductor or transformer.
?
 
  • #10
How can we talk about phase shift if our input voltage is not a sinewave? For a square wave voltage across an inductor we get triangle wave for the current as well as for the flax.

I think that you should back to basics and start studying DC/DC converters.
And I highly recommend you to read this pdf starting from page 22 "Understanding the Inductor".
http://www.elsevierdirect.com/samplechapters/9780750679701/9780750679701.PDF
 

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