EECS 100 Circuit Elements Laboratory B Boser University of California Berkeley Department of Electrical Engineering and Computer Sciences EECS 100 Professor Bernhard Boser LABORATORY 3 v1 CIRCUIT ELEMENTS The purpose of this laboratory is to familiarize ourselves with the concept of circuit elements Anything that has electrical connections can be viewed as a circuit element The resistors and solar cells we worked with in the first lab are circuit elements as are the power supply and multimeter The circuit element abstraction lets us to focus on the relationship between currents and voltages at the interface of the element without having to worry about the complex circuitry inside of it We already made use of this abstraction in the first lab when we treated the power supply which contains a very complex circuit inside simply as a constant voltage or current source To successfully apply complicated circuit elements we need means to describe and measure their behavior at the terminals In this lab we concentrate on the current versus voltage characteristics IV curves for short We already have seen IV characteristics of supplies and solar cells in the first lab In this laboratory we will extend our repertoire to include the characteristics of potentiometers an oscilloscope a diode and a transistor In later laboratories we will use our understanding of circuit elements to design electronic circuits This laboratory also uses two new instruments the function generator and the oscilloscope Download and read the instructions before coming to the lab Page 1 EECS 100 Circuit Elements Laboratory B Boser LAB REPORT Lab Session Name 1 SID Name 2 SID 1 Oscilloscope Model Resistors are not only useful circuit elements but are also good models for many electrical devices Here we use a resistor to model a complex electronic test instrument a In the graph below plot the IV characteristic of a 1k resistor for V 5 5V Label the axes scale and units of 1 P of 1 M Measured optional for extra credit b Oscilloscopes are complicated electronic instruments for measuring voltage versus time We will make extensive use of an oscilloscope later in this course but today we treat the oscilloscope as a simple circuit element without worrying about its internals Use the circuit shown below to measure the IV characteristic for V 5 5V and graph do not forget to label the axes your result in the chart provided Make sure that the oscilloscope is turned on when Page 2 EECS 100 Circuit Elements Laboratory B Boser making the measurement After removing the scope probe from the circuit check your result with the ohm meter setting of the multimeter Note use a coax connector with individual red and black cables to connect the scope and tie the black strand to the common terminal of the supply Ask the TA if you are not sure how to do this of 2 M of 3 M What value resistor has the same IV characteristic Extracted resistance 2 Diodes Diodes pass current in only one direction The circuit symbol for a diode is shown above and the direction of the triangle indicates which direction current can flow through it In other words a diode acts like a short circuit for current flowing in the direction of the arrow and like an open circuit for current flowing in the opposite direction a Based on the description above plot the IV current versus voltage characteristic of an ideal diode in the graph below part b b Measure and graph the IV characteristic of a diode and plot the result in the graph below Do not forget the tickmarks 0 1V 0 2V etc Use the test circuit shown below The resistor limits the current Page 3 EECS 100 Circuit Elements Laboratory Ideal and measured diode IV characteristics B Boser of 3 P of 5 M c Sketch the voltage VR1 across resistor R1 1k in the circuit below Vin is a sinusoidal voltage with peak amplitude 5V 3 5 Vrms Assume that the diode is ideal Plot the expected value of VR1 as a function of time and verify your result by simulating the circuit with Multisim In the laboratory substitute the function generator for Vin and program it for a 1kHz sinusoidal output with 5V peak to peak amplitude and zero offset verify with the oscilloscope Connect the oscilloscope across R1 use a probe with 10x attenuation and transfer the measured waveform to the graph below Try also square wave and ramp signals Page 4 EECS 100 Vin Circuit Elements Laboratory B Boser R1 Expected waveform of 1 P Multisim simulation result of 3 P Measurement of 3 M Explain discrepancies of 1 M d The circuit shown above is called a half wave rectifier since it passes only the positive half of the sine A variation using 4 diodes is used in wall transformers to generate the output shown below Can you figure out the correct circuit for extra points Circuit diagram optional of 3 Page 5 P EECS 100 Circuit Elements Laboratory B Boser 3 Field Effect Transistor The transistor is arguably the most important circuit element Unless you are an integrated circuit designer a specialization within electrical engineering you will rarely deal with individual transistors but rather use integrated circuits with several transistors inside that have more functionality than a single transistor But sometimes a single transistor is just what we need and in this lab we are going to measure transistor characteristics The picture on the right shows an IRF 510 a so called N Channel enhancement mode silicon gate power field effect transistor It has three terminals Drain D gate G and source S Corresponding circuit symbols are shown on the right Transistors are quite universal and can be used as on off switches programmable resistors or current sources We call the voltage difference between drain and source VDS similarly the voltage difference between gate and source is VGS In this section of the lab the switch like behavior of the transistor is demonstrated The transistor is like a switch in the sense that it has two states an on state low resistance between drain and source and an off state high resistance between drain and source The gate voltage determines which state the transistor is in When VGS is below some threshold the switch is off and the resistance between drain and source is high When VGS exceeds the threshold the switch is on and the resistance between drain and source is lower D G S a Use the circuit shown below to measure the resistance between the drain and source terminal as a function of VGS and plot your result using a logarithmic scale for resistance Keep VDS 1V
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