1. Rowan Hall 238A beard@rowan.edu http://rowan.jkbeard.com April 24, 2007 Electronics I for M.E. ECE 09-311 2 Load Line Exercises James K. Beard, Ph.D.

2. Slide 2 Electronics I for M.E. April 24, 2007 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

3. Slide 3 Electronics I for M.E. April 24, 2007

4. Slide 4 Electronics I for M.E. April 24, 2007

5. Slide 5 Electronics I for M.E. April 24, 2007

6. Slide 6 Electronics I for M.E. April 24, 2007 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

7. Slide 7 Electronics I for M.E. April 24, 2007 The Voltage Transfer Characteristic 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

8. Slide 8 Electronics I for M.E. April 24, 2007 Saturation line Cutoff line Load line

9. Slide 9 Electronics I for M.E. April 24, 2007 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, V f = 0.7 Volts

10. Slide 10 Electronics I for M.E. April 24, 2007 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 V f 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

11. Slide 11 Electronics I for M.E. April 24, 2007 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 V TR 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