MARK: 100 ELECTRICAL ENGINEERING DEPARTMENT ELCTRONIC COMPUTER AIDED DESIGN (EC302) TOPIC LAB WORK OBJECTIVES : : : TRANSIENT ANALYSIS (CLO3) 04 At the end of this session, students should be able to: 1. Open a new file 2. Generate schematic diagram 3. Run Transient Analysis 4. Generate the input and output signal THEORY A Transient analysis generates output similar to that normally shown on an oscilloscope, computing the transient output variables (voltage or current) as a function of time, over the user-specified time interval. During Transient Analysis, first an initial operating point is calculated (based on dc values) and after that all momentary voltages and currents are computed as the result of a time dependent voltage or current source - including, of course, the influence of capacitors and inductors as well as all non-linearity’s (clipping effects due to voltage limits etc.) The Transient response analysis causes the response of the circuit to be calculated from TIME = 0 to a specified time. Since transient analysis is dependent on time, it uses different analysis algorithms, control options with different convergence-related issues and different initialization parameters than DC analysis. However, since a transient analysis first performs a DC operating point analysis (unless the UIC option is specified in the .TRAN statement), most of the DC analysis algorithms, control options, and initialization and convergence issues apply to transient analysis. are presented in the Grapher View. There are three possible responses: α < ω0 : Underdamped response α = ω0 : Critically damped response α > ω0 : Overdamped response . the results. 2. Multisim performs Transient Analysis using the following process: 1. This analysis divides the time into segments and calculates the voltage and current levels for each given interval. They are defined by: The value of the damping factor (α) in relation to the natural frequency (ω0) determines the behavior of the circuit’s response. Capacitors and inductors are represented by energy storage models. Multisim computes the circuit’s response as a function of time. AC sources have time-dependent values. A DC Operating Point Analysis is performed for each time point in the cycle. the characteristic equation modeling this circuit can be represented as: Where α is the damping factor and w0 the natural frequency (or resonant frequency). The solution for the voltage waveform at a node is determined by the value of that voltage at each time point over one complete cycle. According to the theory. Each input cycle is divided into intervals.A Introduction In Transient Analysis. Numerical integration is used to calculate the quantity of energy transfer over an interval of time. 3. voltage versus time. Running Transient Analysis Consider the series RLC circuit shown in Figure 1. Finally. Assumptions: DC sources have constant values. also called time-domain transient analysis. Figure 1. In this example you will use Transient Analysis to plot the step responses of the RLC circuit. Table 1 describes the Analysis Parameters tab in detail. providing the transient response of the selected output variables starting at time 0 seconds and stopping after 1 ms. 200Ω and 1 kΩ. the RLC circuit is driven towards an over damped response.Note that as the value of α increases. The default settings are appropriate for normal use. Since α depends on the value of the resistance. Series RLC circuit. Complete the following steps to configure and run a Transient Analysis: 1. The Transient Analysis window opens. Draw the circuit in Figure 1 2. you will use three different values for R: 40Ω . Select Simulate»Analyses»Transient Analysis. . User-defined. Maximum time step the simulation can handle. Parameters used in Transient Analysis. Enable as desired. Maximum time step (TMAX). End time (TSTOP) End time of Transient Analysis. Parameter Initial Conditions Meaning There are four options: 1. it uses user-defined initial conditions. Multisim tries to start the simulation using the DC operating point as the initial condition. Must be greater than or equal to 0 and less than end time. There are three options: settings (TMAX) 1. Calculate DC operating point. 2. The analysis starts from initial conditions as set in the Transient Analysis window. Multisim first calculates the DC operating point of the circuit.Table 1. Automatically determine initial conditions. (TSTEP) Estimate maximum This becomes enabled when the Maximum timestep (TMAX) checkbox time step based on is selected. Minimum number of points between start and stop times. then uses that result as the initial conditions of the Transient Analysis. Set initial time step Enable to set a time interval for simulation output and graphing. Enable to generate time steps automatically. Maximum time step Enable to manually set time steps. If the simulation fails. 2. Generate time steps automatically. 4. netlist (TMAX) . Must be greater than start time. Start time (TSTART) Start time of Transient Analysis. 3. Set to zero. The analysis starts from zero initial conditions. Minimum number of time points. 3. You can reset all the parameters to their default values by clicking the Reset to default button. Figure 2. . Analysis parameters for the Transient Analysis. in Multisim you do not have to worry about the complex SPICE syntax.TRAN initializes a Transient Analysis. however. <TSTOP> is the final analysis time.Note: In SPICE. <UIC> is used for initial conditions. <TSTEP> is the time increment for reporting results. the command that performs a Transient Analysis has the following form: . 3. <TMAX> is the maximum step size used in incrementing the time during the analysis. <TSTART> is the start time for reporting results. Note that these are the same parameters that were defined in Table 1.TRAN <TSTEP> <TSTOP> < TSTART <TMAX> > <UIC> Where . Configure the Analysis Parameters as shown in Figure 2. Output variables for the Transient Analysis. Click Simulate. as shown below. and then highlight V(vi) and V(c) from the list.4. Results are displayed in Figure 4. . 7. Click the Add button to move the variables to the right side under Selected variables for analysis. Select the Variables in circuit list. Figure 3. select All variables from the drop-down list. Select the Output tab. 5. 6. The Grapher View window opens. . 8. a similar analysis is performed. Change the value of R to 200Ω 10. You will see the critically damped response. Note: If you connect the Oscilloscope to the circuit and run the simulation. As you can see.Figure 4. 9. Transient Analysis results. Run Transient Analysis for R = 1 kΩ The overdamped response will be plotted. 11. this is the typical underdamped response of a series RLC circuit. Run Transient Analysis once again. Close the Grapher View. however. you can also use Parameter Sweep Analysis to verify the behavior of a circuit when a parameter is varied across a range of values. Step responses of the RLC circuit. merge the plots in one. . In this example you executed the simulation three times in order to get the step responses of the RLC circuit. Figure 5 shows a comparison graph of the results. You can use Overlay Traces from the Graph menu.In order to compare the three results. Figure 5. Part 1 1 Create the Circuit shown in Figure 6 1 2 X1 R3 3 10kΩ 2 1 I1 1kHz 1A R1 10kΩ 2 C1 5pF V1 1kHz 40 V 0 1 SP DT_OP EN C1 5P F 0 Figure 6 Figure 7 The voltage source will be a 0 to 5V pulse signal (Vpulse). You will need to define the parameters of the pulse source. Refering to figure 7. so these instructions will focus on the new features we haven’t used before. We will use a special voltage source in the component library to accomplish this. The purpose of the pulse is to model the behavior of a switch operating between 0V and 5V. Keep the default settings for any parameter not listed below: _ Initial Value = 0V . – Print a copy of your design and put it in your lab report . – To define the parameters of the pulse. it behaves as if the switch is in position 1 and when the pulse is high (5V).B RC Network The purpose of this lab is to analyze an RC network using Multisim. double click on the voltage source and make the following settings in the PULSE VOLTAGE settings window. For the purpose of this exercise. it behaves as if the switch is in position 2. you will create a waveform that is 5V for the first 500ns and 0V for the next 500ns. when the pulse is low (0V). _ Pulsed Value = 5 _ Pulse Width = 500ns(be sure to check the units!) _ Period = 1000ns(units!) _ Double-check the settings and click OK _ The source label should now note the proper voltage and time parameters. You can refer back to last week’s notes to refresh your memory on other portions. then repeats this pattern. as in the diagram above. It is assumed that you remember (or can look up) the software procedures you used last week in Lab 3. It will pull a vertical line of a different color (probably yellow or blue) out into the plot. If you forget this step it will plot fewer points. II. Click the Minimum number of time points button and leave it at 100. which you will see if you re-open this window later). so we must run the analysis for at least the duration of the pulse source period. A Transient Analysis data window will open. From the Simulate menu. Their default position is on the vertical axis. Grab it with your mouse and drag it to the right. Analyzing the Plot: Notice that while the pulse reads 5V from 0s to 500ns. Click the Simulate button and a Grapher View window will appear showing your plot. Specifically. add V(1) and V(2) to the selected variables list so it will plot both the source voltage and the capacitor voltage. At the top of the voltage axis you will see a small colored (probably pink) triangle pointing downward. In the Analysis Parameters tab. There are two cursors. This opens the Transient Analysis parameters window. and drag it into the plot area too. III. select Black and White Color. We will use the software’s Transient Analysis feature to make these observations. Therefore we will set the simulation to run for 1000ns. We want to observe the capacitor for at least one charge and discharge cycle. This ensures that we plot plenty of data points to get a smooth curve. It should look like the one in Figure 8 To toggle the background color between black and white. VI. II. . and the curve will look chunky.000001 into the TSTOP window. from the Graphs menu. so you can go back to the vertical axis. connecting them with straignt lines. you will observe how a 5V source charges the capacitor in an RC network (and how the capacitor discharges in the same network when the source shuts off). from the Cursor menu. Drag it to the vacant area in the upper right of the screen above the discharge curve so we have an unobstucted view of the charge curve. III. Simulating the Circuit: Multisim allows the user to observe how a circuit behaves over time. VII. You can also type “1e-006” if you like (Multisim will translate your decimal value to this notation for you anyway. In the Grapher View window.2 I. the capacitor is shown to be charging. leave the start time at 0 and set the end time to 1000ns (or 1μs) by typing 0. grab the other one. In the Output tab. select Show Cursors. We will use the cursors to make measurements from the plot. select Analyses: Transient Analysis. while during the low portion of the pulse wave (500ns to 1μs) the capacitor is discharging. IV. 3 I. V. (c) Copy and paste the result in your report. (a) A rule of thumb states that the time it takes for a capacitor to charge from 10% to 90% (b) Leaving one cursor at the origin. Move one cursor to where it intersects the curve at a value of 0.5V (90% of 5V).5 and 4. Making measurements: of its maximum value is approximately equal to 2.y) coordinates for the point on the plot where the cursor intersects the plotted curve. And there are separate (x. Watch the values in the Transient Analysis window change as you move the cursor around. We are primarily interested in the capacitor charge and discharge curves for measurement’s sake. There is a separate column for each curve.IV. We won’t be taking measurements of the source voltage however. Using this you can make time and voltage difference measurements for any two points on either curve. Using these cursors you can extract numerical results from the plot. but we have displayed the source voltage on this plot to help us remember what the state of the source is for the charge and discharge scenarios.5V(10% of 5V) and the other to 4. X represents the time value and Y represents the voltage value. so you can ignore that column in the analysis window. Read the capacitor voltage at this point. . VI. When you are as close as you can get to 0. Keep track of the voltage value the cursor is at by watching the Transient Analysis window.2 to calculate the time constant. Name this output as “RC=50ns”. Divide this time value by 2. How does this number compare to the RC time constant value by calculation? V.y) values for each cursor. take note of the elapsed time difference between them. for each curve. the analysis window also calculates the difference between the X and Y values for the two cursor positions (and it calls these dx and dy). Note that.5V.2 times the time constant for that circuit. position the second cursor at the 150ns mark. This data represents the (x. Figure 8 . Fully label your schematic. Save your drawing. We also want to use a shorter period of time for this plot because the time constant is shorter than the first circuit. Configure the Transient Analysis: Remember from earlier.C SERIES AND PARALLEL RC NETWORKS R2 R1 1 V1 1kHz 40 V 0 83. Using what you know about the series and parallel relationships of resistors and capacitors. you want to be sure you’re plotting at least 100 points (check the box). This will increase our accuracy when picking points on the plot. VI. Create the circuit in Figure 4 using Multisim. Use the full diagram rather than your reduced version. II. configure a pulse signal with a 40V peak amplitude that is 150ns in length. . Also. IV.33kΩ 3 50kΩ R3 50kΩ R4 50kΩ C1 100PF C2 100PF 2 I. leave the start time at 0 and set the end time to 500ns. Use aperiod of 300ns. For Vs. go to the Simulate menu and select Analyses: Transient Analysis. Fully label your plots. III. V. What is the RC time constant for the circuit? Sketch the capacitor charging and discharging curves using the 2/3 approximation method. Remember to close the old design file and start a new one for this circuit. and tape it into your lab book. reduce the schematic in to a circuit with a single equivalent resistor and capacitor. In the Analysis Parameters tab. print out a copy (make it small enough to fit nicely in your lab book!). VII. Copy of the plot that shows the cursors in the 10% and 90% of total voltage amplitude positions and paste it in your lab report. VIII. Insert a name and the time constant information in the plot title. this means you’ll have to look at the net report to determine which net connects C1 and C2 (or double click on the wire that connects them and it will tell you how it has named that node). There is more than one voltage that will look like a capacitor charge/discharge curve so you must first confirm the correct one.. . Determine the time constant for this circuit by using the 10% to 90% risetime method. There will be several voltages to choose from. Simulate and analyze your circuit as before. and you want to plot Vceq which is the voltage across the parallel capacitors. as usual. Remember too that you’ll have to add the proper variables to the list in the Output tab.. 98kΩ 3 C4 3 6 2 4 741 R3 80kΩ 10nF 10nF 7 1 5 741 100mVpk 1kHz 0° C2 1nF 0 R7 22. Use Transient Analysis to see current drawn both from the input and output of the filter. s): R5 22.98kΩ Probe_Input V4 R2 3. The Band-Pass filter was built by cascading a High-Pass Filter and a Low-Pass Filter.5kΩ U1 C3 6 2 4 low passout 11..D Band-pass Filter This example uses Transient Analysis to plot the current drawn both from the input and output of a Band-pass filter.3kΩ U2 1 Probe_Output R1 V: V(p-p): V(rm . s): 3.5kΩ V3 12 V R4 20kΩ V1 12 V R8 1kΩ ... Choose Simulate/Analyses/Transient Analysis V2 12 V R6 C1 1µF 7 1 5 V5 12 V V: V(p-p): V(rm .. V1 160 V D2 MUR160 X1 MTP6N60/MC U1 2 3 0 D1 MBR20100 L1 2.Current Mode PWM Control The two-switch Forward Converter topology consists of two MOSFET switches X1 and X2. X1 and X2 are turned ON and OFF simultaneously. a power transformer U1. When they are ON power is delivered to the load through the transformer and the output filter. When the MOSFETs are turned OFF power flow in the primary circuit is cut off. Choose Simulate/Analyses/Transient Analysis view the output voltage of the circuit in Grapher View.22kΩ U3 2SWITCHCM ISENSE COMP FB VOSC OUT1 GNF OUT2 GND LLEAK1 10µH C2 775pF C3 2.65nF R5 20kΩ RGL1 15Ω X2 MTP6N60/MC R6 1. and the voltage on the primary winding will reverse until pin 0 of U1 is clamped to GND by D2 and pin 1 of U1 is clamped to VIN by D3.22kΩ R7 12kΩ CLEB1 100pF R8 1kΩ RSENSE1 284mΩ . and an output filter.3µH R1 1mΩ Vout R2 3mΩ RLOAD1 80mΩ C1 4mF Pout=300W CCM D3 MUR160 1 LMAG1 1mH RATIO = 180m D4 MBR20100 RGUP1 15Ω R3 134mΩ R4 1. two clamp diodes D2 and D3. In this topology the voltage stress on each MOSFET is clamped to the input voltage. two rectifier diodes D1 and D4.E Two-switch Forward Converter . Choose Simulate/Analyses/Transient Analysis. The smaller the equivalent resistor value. Observe the settings for Start time (TSTART) and End time (TSTOP).F Frequency Divider with Adjustable Duty Cycle This example describes how easily the tau constant of an RC circuit can be used to adjust the duty cycle of a waveform. When the capacitor voltage reaches 2V the output of the circuit goes low by the use of an inverting gate.2kΩ C2 2..2nF R2 2. the smaller the capacitor charge time. Click Simulate. Choose Simulate/Run to view the operation of the circuit using the virtual instrument.2kΩ U1B R1 1MΩ 50% Key=A D1 V1 4V VCC 5V GND U1A C1 2..2nF Pow er Supply for Digital Parts 74HC04N_4V V2 1kHz 5V 74HC04N_4V 1N4148 U1C D2 1N4148 74HC04N_4V C3 2nF . By keeping the input frequency constant the duty cycle of the output waveform is changed only through potentiometer R1. XSC2 Ext T rig + _ A + _ + B _ IN input V: V(p-p): V(rm . When the voltage on the capacitor drops below 2V the output of the circuit goes high. This example uses Transient Analysis to see the circuit behavior over a specific time span. Use Transient Analysis to see the Transient Response over a specific time span. s): R3 2. rather than twice the input voltage that is usually the case in push-pull and forward converters.8mH J2 1 3 0 U2 2 12 1 D2 DBREAK D3 rect L1 81uH R2 70mΩ COUT1 156uF IC=27.6Ω R5 12.512 RLOAD1 7Ω DBREAK D4 SBREAK 1V0V R7 500.G Half-Bridge Converter with Transformer . providing a constant potential of one-half of the input voltage at their junction.5V out RATIO=0. equal capacitors connected in series across the DC input.6525nF R3 20kΩ REF=5 RATIO=1 U6 PUSH_CM ISENSE COMP FB VOSC OUT1 OUT2 GND 0 U1 2 3 1 CUP1 10uF SBREAK 1V0V R4 894mΩ LMAG1 5. The transistor switches S1 and S2 are turned ON alternately and are subjected to a voltage stress equal to that of the input voltage. J1 D1 DBREAK R1 2.5mΩ C3 470pF CLOW1 10uF ABM1 ABM_VOLTAGE Choose Simulate/Analyses/Transient Analysis view the output voltage of the circuit in Grapher View.Current Mode PWM Control The Half-Bridge DC-DC converter configuration consists of two large. In this example Transient Analysis is used to simulate the output characteristics of a Current Mode Control Half-Bridge Converter.3027kΩ C1 HT 775pF V1 160 V C2 2.77kΩ R6 1kΩ ABM DBREAK D6 DBREAK D5 DBREAK RESR1 76. . The primary switches alternately power their respective windings.91 DBREAK D4 RESR1 152mΩ SBREAK 1V0V S2 DBREAK R4 sum R5 1kΩ C3 100pF RSENSE1 1.001kΩ RT D6 DBREAK D Choose Simulate/Analyses/Transient Analysis view the output voltage of the circuit in Grapher View.6047kΩ V1 4 U1 1 D1 DBREAK D2 rect L1 81uH R2 70mΩ COUT1 74.8mH R1 4.8uF out 3 160 V C1 775pF C2 2.H Push-Pull Converter .772kΩ R6 1.789Ω SBREAK 1V0V D5 DBREAK 12. LM1 5.Current Mode PWM Control A push-pull converter is a type of DC to DC converter that uses a transformer to change the voltage of a DC power supply. I Data . The Push-Pull topology is basically a forward converter with two primaries. Analysis and Report ( Instructions as in Lab 01) .8mH 2 0 DBREAK D3 RLOAD1 7Ω drain1 S1 RATIO=3. In this example Transient Analysis is used to simulate the output characteristics of a Current Mode Control Push-Pull Converter.6525nF R3 20kΩ REF=5 RATIO=1 U3 PUSH_CM ISENSE COMP FB VOSC OUT1 OUT2 GND LM2 5.