UNIVERSITY OF CALIFORNIA BERKELEY EE100 Summer 2008 Lab 2 Equivalent Circuits Guide Important Notes Please make sure the current limit set higher than the current required by the circuit but lower than 2 amps This is to ensure that you provide your circuit with enough power without damaging the equipment Always use measuring devices DMM to take your measurements Do not depend on the power supply to report accurate voltage and current values In this lab you will use 1 2k 2 2k 220 and 1k resistors For this lab you can use resistor values are at within 10 of your theoretical value If you require the use of other valued resistors then your theoretical calculations are incorrect These circuits are complicated Good breadboard practice will be key in completing this lab Equivalent Resistor Networks 2 2k 2 2k DC 2 2k 2 2k Figure 1 1 Build the circuit shown in Figure 1 To demonstrate the importance of a neat and orderly breadboard layout use only the resistors and no extra wires except those connecting o the power supply to build this circuit Assuming a maximum of 10 volts what is the maximum amount of current supplied by the power supply 2 From your prelab you calculated the theoretical resistance across A and B Disconnect the circuit from the power supply and use the DMM to measure the actual resistance across terminals A and B 3 Reconnect the power supply and record VAB and I for 5 different supply voltages between 0 and 10 volts Plot the IV curve of this circuit a When recording the value of VAB and I it is important that you use the digital multimeter DMM to take your measurements The readings from the power supply are inaccurate b Please set the current limit of the power supply to a value higher than that calculated in Step 1 but lower than 2 amps DC Req Figure 2 4 Build the circuit shown in Figure 2 Use the value of Req calculated in the prelab exercises and measured in step 2 5 Using the power supply record VAB and I for 5 different supply voltages between 0 and 10 volts Plot the IV curve of this circuit Th venin s and Norton s Equivalence 1 2k 7V C 1 2k D RL 2 2k 220 Figure 3 6 Build the circuit shown in Figure 3 leaving out the resistor labeled RL for now Again use only the resistors and no extra wires to build this circuit Measure the voltage across terminals C and D This is your open circuit voltage VTH and should be the same as you calculated in your prelab 7 Now measure the current flowing through terminals C and D Remember when measuring current using the DMM there is 0 resistance across the probes Then you are essentially measuring the short circuit current ISC and should be the same as you calculated in your prelab 8 Disconnect the power supply and short terminals A and B You killed the voltage source Measure the resistance across terminals C and D This is your Th venin resistance RTH and should be the same as what you calculated in prelab 9 Now unshort terminals A and B and reconnect the power supply thus restoring the circuit in figure 3 For 3 different values of RL 220 1 2k and 2 2k install the resistor and measure the voltage across and the current through RL Vth RL Figure 4 10 Build the circuit shown in Figure 4 with the appropriate values of VTH and RTH you calculated in your prelab and measured in steps 6 and 8 11 For the three values of RL measure the voltage across and current through RL ISC Rth RL Figure 5 12 Build the circuit shown in Figure 5 with the appropriate values of ISC and RTH that you calculated in your prelab and measured in steps 7 and 8 Hint to make a viable current source connect a large RTH resistor in series with the power supply and adjust the voltage of the power supply until the current through the resistor is ISC 13 For the three values of RL measure the voltage across and current through RL Pure Resistive Networks and Frequency 14 Attach the oscilloscope channel across points C and D on figure 3 This is the system output Disconnect the power supply and instead attach points A and B to the function generator This will apply an AC rather than DC input to the system Attach a second oscilloscope channel across points A and B 15 Output a 1 kilohertz sinusoidal wave with function generator 16 Observe both input and output waveforms together on the oscilloscope screen Vary the frequency of the sine wave Circuit Simplification and Symmetry B C A D F E H G Figure 6 17 Build the circuit in figure 6 on the breadboard Make all resistor values 1k As mentioned in the prelab this circuit should be constructed in a neat and orderly fashion using only the resistors and no extra wires Hint node A and F are the voltage source and ground respectively Remember the breadboard configuration need not resemble the circuit s spatial configuration Only the connections between nodes matters 18 Measure Req between points A and F Compare this to the value you calculated in the prelab 19 Reconnect the power supply to points A and F Adjust the voltage such that the total current supplied is 10 mA Measure the current through the resistor between point A and D
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