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## Electronics I for M.E. ECE 09-311 2 Load Line Exercises

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**Electronics I for M.E.ECE 09-311 2Load Line Exercises**James K. Beard, Ph.D.**The Load Line**• Definition: v-i curve of Thévenin equivalent of a linear circuit • Purpose: To provide a graphical interface with a nonlinear circuit element such as a diode or transistor • Usage: • Draw v-i curve of the nonlinear element, • Draw load line over it, and • Intersection of the lines is the operating point. • Examples follow for BJT, MOSFET, and diode Electronics I for M.E.**Input-Output Voltage Curve**• Called the voltage transfer characteristic curve • A plot of the output voltage versus the input voltage • The voltage transfer characteristic from load line: • Draw the family of transistor v-i curves • Draw the collector load line • Find the proper transistor v-i curve from an input voltage, • Read the output voltage from the load line intersection • Construct a table of input voltages versus output voltages and plot the table Electronics I for M.E.**The Voltage TransferCharacteristic From Load Line**• Draw the family of transistor v-i curves • Draw the collector load line • For each of a set of input voltages • Find the proper transistor v-i curve for this voltage, • Read the output voltage from the load line intersection with the v-i plot, and • Add the result to a table. • Plot the table Electronics I for M.E.**Saturation line**Load line Cutoff line Electronics I for M.E.**Exercise 1: The Diode v-i Curve**• Draw a load line for a 6 V source and a 75 Ohm resistor over the diode v-i curve • Read the voltage and current at the intersection • Check the results by using a constant voltage drop model for the diode, Vf = 0.7 Volts Electronics I for M.E.**Exercise 2: The BJT v-i Curves**• Draw a load line for a 15 Volt source and a 750 Ohm collector load resistor • For a base series resistance of 1 kOhms and Vf equal to 0.7 Volts: • Find the base current for input voltages of 1.7 Volts, 2.7 Volts, etc. and • Find the output voltages from the intersections of the proper v-i curves with the load line and put them in a table • Plot the table Electronics I for M.E.**Exercise 3: The MOSFET v-i Curves**• Draw a load line for a 20 Volt source and a 400 Ohm drain load resistor • For a threshold voltage VTR of 2 Volts: • Find the drain current for input voltages of 2 Volts, 3 Volts, etc. and • Find the output voltages from the intersections of the proper v-i curves with the load line and put them in a table • Plot the table Electronics I for M.E.