Question

Objectives: To learn transient behavior of series RC circuits To observe of time constant and its effect on charging process of capacitor using pulse waveforms Equipment: Oscilloscope Function generator Resistors (1 k) Capacitors (1 uF) Breadboard Pre-Lab Questions A pulse is a voltage or current that changes from one level to the other and back again. If a waveform's high time equals its low time, it is called a square wave. The length of each cycle (one positive peak and one negative peak) of a pulse train is termed its time period (T) The pulse width (tp) of an ideal square wave is equal to half the time period. sec (eqn. ) The relation between pulse width and frequency is then given by (Units: ) (eqn. 2) 1.Write down the equation for time constant of a capacitor charging circuit. Mention units 2. Write down the equation for voltage across the capacitor during the charging process 1. Mount the series RC eircuits on breadboard as shown in fig. (1) Figure 1: Series RC eircuit 2. Connect function generator output to series RC circuit. 3. Connect Channel of the oscilloscope to monitor the source/input signal. 4. Connect Channel 2 of the oscilloscope to monitor the voltage across the capacitor Calculate the time constant for the circuit. Mention units and show calculations below. Also mention time required for circuit to attain steady state (5 t) s. Calculate the pulse width (t) of square waveform to observe steady state characteristics (t, 5 ) and also calculate frequency (f) using eqn. 2 in pre-lab questions section. Part I: Charging the capacitor under a pulse width equal to 5r 6. Generate the square wave of 10 Vp, and frequency 100 Hz using function generator. 7. Set the oscilloscope to dual mode to observe the input and output signals simultaneously. 8. Observe the voltage across the capacitor at different time instant and record the values in table I 9. Draw the observed capacitor voltage waveform on graph sheet. Table I: Voltage across the capacitor Timdime (s) v,(t) (V) (Mcasured) ) (V) (Calculated) constant 2r 3 r 4 r 5 r Part II: Charging the capacitor under a pulse width that is much less than 5r Determine the frequency of the waveform having a pulse width t, equal to 0.5 times the pulse width in step 5 and also calculate frequency (f). Show calculations below. 10. 11. Generate a 10 V Pp square wave signal at the trequency determined in Step 10. Observe the waveform on Channel 1 of the oscilloscope 12 Set up the circuit shown in Figure 1 using the signal generated in Step 11 as input 13. Connect Channel 2 of the oscilloscope to observe the change in voltage across the capacitor. 14 Set the oscilloscope to dual mode to observe the input and output signals simultaneously 15. Identify and note the maximum voltage that the capacitor attains and the time taken to charge. Махіmum capacitor voltage the асross (Oscilloscope measurement) Time taken for capacitor to attain maximum voltage: (Oscilloscope measurement) 1 Draw the observed capacitor voltage waveform on graph sheet Part IlI: Charging the capacitor under a pulse width that is much higher than 5r 17. Determine the frequency of the waveform having a pulse width equal to 10 times the pulse width in step 5 and also calculate frequency (). Show calculations below. I8. Generate a 10 Vp square wave signal at the frequency determined in Step 17. Observe the waveform on Channel 1 of the oscilloscope. 19. Set up the circuit shown in Figure 1 using the signal generated in Step 18 as input 20. Connect Channel 2 of the oscilloscope to observe the change in voltage across the capacitor. Identify and note the maximum voltage that the capacitor attains and the time taken to charge. Maximum 21 voltage the capacitor: 22 аcross (Oscilloscope measurement) 23 Time taken for capacitor to attain maximum voltage: (Oscilloscope measurement) 24. Draw the observed capacitor voltage waveform on sheet. graph Mention the effect of changes in pulse width on maximum voltage across capacitor. 2. Comment on the time required by capacitor to attained steady state for given circuit. 1.

Answer 1

1) With increase in pulse width, the maximum voltage across the capacitor will increase until a steady state value is reached.

2) The time required to reach the steady state value is 5 times the time constant or 5RC.