Objectives: Lab 5: Time Proportioning Control After performing this experiment, you will be able to: 1. Control the average voltage/power delivered to the load using Time proportioning method. 2. Measure the duty cycle of the Pulse Width Modulated (PWM) signal. Procedure: 1. Construct the following circuit using multisim. R2 10ΚΩ Key=A 0% VCC 10V VCC 10V XSC1 A B U1 3 V1 + ཀ་ 5Vpk 60Hz 2 741 0° Offset = 5V Ext Trig Figure 1: Time proportioning circuit 2. Set the potentiometer to 0% and Run the simulation. Observe the oscilloscope; you should be able to see a positive DC voltage because the op-amp is saturated. Means the voltage at the non- inverting terminal is greater than the inverting terminal. 3. Measure the dc output voltage using the voltage probe at pin 6. Record the result in table 1 below under output voltage. 4. Set the potentiometer to 10%; you should be able to see the following waveform. Oscilloscope-XSC1 < T1+ T2 → T2-T1 Time 617.176 ms 630.054 ms 12.879 ms Channel_A Channel_B 9.118 V Reverse 9.118 V -297.448 uV Save Ext. trigger Timebase Scale: 10 ms/Div Channel A Scale: 5 V/Div Channel B Scale: 5 V/Div Trigger Edge: FABExt X pos. (Div): 0 Y pos. (Div): 0 Y pos. (Div): 0 Level: 1 V Y/T Add B/A A/B AC 0 DC AC 0 DC - Single Normal Auto None Figure 2: Measuring ON time of the pulse 5. Place the cursors 1 and 2 at the beginning and ending of the pulse as shown above. 6. Observe the value of T2-T1, which gives the ON time of the pulse. Record the result in the table 1 below under ON time (ton). Potentiometer setting Output ON Time (ton) Duty cycle Voltage 0% N/A 100% 10% 30% 60% 90% 100% N/A 0% Table 1: Duty cycle measurement 7. Now place the cursors such that time period (T) of the waveform can be measured as shown below. To measure the time period cursors must be place to cover one complete cycle. This time period will not change since the frequency of the signal stays at 60Hz. Oscilloscope-XSC1 Figure 2: Measuring time period of the waveform 8. The measured time period (T) is ¸ 9. Calculate the duty cycle using the formula below. Record the duty cycle in table 1 above. % DC = ton T * 100 10. Record the dc output voltage using the probe under output voltage. 11. Now, change the potentiometer setting as listed in table 1 above and repeat steps 5 through 10. Experiment Questions: 1. The term duty cycle refers to the amount of time a signal is compared to the period of one complete cycle. A. off B. on 2. The output voltage of op-amp is positive saturation, when the voltage applied to the input is greater than the A. inverting input. B. noninverting 3. A square wave that is 20V at its high state and OV when it is off will produce an average DC voltage of A. 7.5V when its duty cycle is 75%. Formula: VOUT = Duty Cycle * Peak voltage B. 10V C. 15V