Multisim Dc Sweep Analysis

[John]

Inthis case, the 1N4462 component has a Zener voltage (VZ) of 7.5 V and a 5% tolerance. The minimum and maximum input voltages that can be regulated by the Zener diode are 7.41 V and 26.41 V respectively. You will use DC Sweep Analysis to study the behavior of the regulator circuit when the input voltage is varied from 0 V to 40 V.

From the Grapher View you can observe that the output voltage steadies at around 7.5 V, which is the nominal Zener voltage for the 1N4462. Use the cursors to calculate the minimum and maximum voltages that this component can regulate.

Note that a second sweep variable (V2) has been added so that the analysis can perform a nested sweep. The first sweep (V1) will be done for each value of the second sweep. The number of output curves will be equal to the number of points for the second source.

The behavior of a circuit is affected when certain parameters in specific components change. With Parameter Sweep Analysis, you can verify the operation of a circuit by simulation across a range of values for a component parameter. The effect is the same as simulating the circuit several times, once for each value. You control the parameter values by choosing a start value, end value, type of sweep that you wish to simulate and the desired increment value. There are three types of analysis that can be performed on the circuit while the component is manipulated: DC Operating Point, Transient Analysis and AC Analysis.

You will find that some components have more parameters that can be varied than others. This will depend on the model of the component. Active components such as op-amps, transistors, diodes and others will have more parameters available to perform a sweep than passive component such as resistors, inductors and capacitors. For example the inductance is the only parameter available for an inductor as compared to a diode model that contains approximately 15 to 25 parameters.

Dictates how to calculate the interval between the start and stop values. Parameter Sweep Analysis plots the appropriate curves sequentially. The number of curves is dependent on the type of sweep as shown below:

I have designed a voltage regulator on Multisim with an AC voltage input, transformer, bridge rectifier and zener diode. I would like to simulate and analyse the line regulation of the regulator. This requires varying the AC voltage magnitude and see if there are any changes to the output voltage.

I was considering using the Parameter sweep to change the magnitude of the AC input however this does not seem to be working - please see screenshots of analysis setup and resulting waveform of the AC input:

As can be seen, even though I have set the settings so that the AC magnitude changes from 200 to 300V RMS in 10V steps with each iteration, the graph shown shows that the voltage does not change between each iteration.

When you define a parameter, for example if you want to sweep amplitude of the AC source you create parameter "Amplitude" and you put (you literally write the world Amplitude) that parameter in the "Voltage(PK)" instead of voltage value, after it will appear in the settings of analysis.

But, when shunt resistances are added, with the current source being fixed of course, the sweep's max voltage is of course lower due to the added parallel path. Therefore, I had to go back to the voltage source which doesn't work.

When a pot is paralleled with two equal value resistors, one above and below the wiper, the domain and range should not change. Rather, only the slope should change across the domain. Specifically, at the lower half of the sweep, [0,5k), the slope should be positive but then decrease as 5k is approached. Then 5k becomes an inflection point. Finally, at the upper half (5k,10k], the slope should gradually increase as 10k is approached. The graph should exhibit symmetry around the vertical line R=5k.

Also, was the circuiit you posted already set up for the analysis? Once I get this information I will try it again and see what I can do, but I still do not believe I am going to be able to do anything with it, but I will try.

It's a combination of two sweeps: a parametric and a dc sweep. I swept what I thought was the potentiometer's wiper and found the dc point with each change of the pot's wiper, but Multisim produced inaccurate results.

Understand that the line I'm calling Vwiper is actually the voltage at the wiper with a resistor in series. To get the actual voltage at the wiper itself, the series resistance can be made very small. What I'm trying to do is I'm trying play with the linearity of the pot, examine how each resistor affects the overall slope (the linearity), the character of the Excel plot.

Through doing it the hard way, using the voltmeter and making one change at a time, I've been able to demonstrate my hypothesis to myself, finally, but it'd be so much nicer, much more presentable, if I could make changes on-the-fly and then port the results to Excel. I just haven't been able to pull off what I can do manually using Multisim's sweep option.

What I've found is that the sweep only works when the pot stands alone (plus an impossibly high shunt resistance, so as to name the line of the output variable) and is driven by a current source that produces the desired max voltage. However, when shunting real-valued resistances are added, the current source also feeds the parallel path, of course, so the numbers are wrong again. Hence, I went to a voltage source again, but the numbers are still wrong. Thus, in order to get the results I was expecting, I could only manually perform the sweep, by using a series of manual pot changes, and with each change, I manually transfered the voltmeter's number to Excel.

It seems I've set up the sweep correctly, because, with only the current source, the pot's wiper seemed to change, based on the results. Likewise, in the resistance sweep (parametric sweep), it shows the current resistance value for the variable selected in the drop down box; you can change the wiper manually and then go back and note that the current value changes, reflecting your manual change, proving you're looking at the wiper and not the resistance from end-to-end.

I even tried a current source (which it liked alone) into the pot and a voltage source across the shunt resistances (which it also likes,) but the sweep still produced bad numbers. I found that what could be done manually just couldn't be done automatically. The only other thing I can think of is maybe I'm, despite the evidence of the wiper change, still not using the appropriate variable, as, in truth, I really don't understand what it means by "r1:xr1," while I couldn't seem to find any explanations in the manual for the various esoteric expressions available in that drop down list.

But I'd sure like to figure this thing out, as this would be a wonderful way to demonstrate Multisim's ease of use and capability. It takes time to manually tweak the pot and then transfer the new voltage drop number to Excel, time that, for the impatient people I work with, I don't have. However, were I to copy a new column of numbers into a second Excel sheet with each sweep, well that would be quite acceptable, as it'd make for an on-the-fly cause and effect demonstration.

Incidentally, assuming you have Excel, I'm also attaching an Excel output that demonstated the pot sweep worked when the pot stood alone and was driven by the appropriate current source. This plot will also show you the plot I'm trying to get when I add the other resistors to the circuit. (By hanging the "_none" suffix on the filename, I'm showing this data was gathered from only the stand-alone pot, with no other resistors, aside from the impossibly large shunt resistor explained earlier.)

Here's one more thing that I thought might help us. I've attached a .gif capture of the parameter sweep window. This window shows the "r1:xr1" option chosen, and it shows that the current position of the pot's wiper is 100% (10000 ohms). Try changing the pot's wiper position and you'll see that that number changes, verifying that we're looking at the right thing.

My experience with teaching SPICE and Multisim in ELEC2210is that live tutorials done in classturned out to be most effectivecompared to written tutorial and video tutorials, andthat is what we will rely on in the later partof this class for CMOS circuits.I will still provide screenshots embeddedin the notes of relevant chapters.

Multisim is available in ECE 308 and310 computer labs, with Elvis drivers.It is also available in the basementcollege of engineering computer labs, it may not havethe Elvis drivers.This likely means all other engineering computer labs shouldalso have it, e.g. in Shelby or Aerospace labs.

It is in some case easier to use thanother SPICE based simulators,e.g. Pspice,butcan be harder to use in other cases.One practical reason for usingMultisim is that it supportsvirtual instruments simulation,which will be useful asthe new 2210 labs use the new NI ELVIS II+ prototypecircuit board.

Note the standard components toolbars, the virtual components toolbar, and thevirtual instruments toolbars. For teaching purpose, we will first use virtual components.Unfortunately, by default, the virtual components toolbar is not shown, so we will needto turn that on as follows:

Ground is under Power_sources in Multisim.Like other SPICE based circuit simulators, it is mandatory tohave the proper ground which is the reference point for allthe nodal voltages simulated.This ground is known as the 0 node in most SPICE based simulators.

Wiring is both particularly simple and particularlydifficult in Multisim. The chanceis that you will first find the wiringsimple or simpler than other programs you used before,at least forsimple circuits.Whenthe cursor is close to the unconnected end of any component,it will change into a small black connection dot and crosshair.A click on the end of the component starts the wiring.Move the cursor to where you want it to be connected.The routing of the wire isby default automatic, but manual adjustment is possible.

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