Homework 7 EE 461G Spring 2000
SPICE Simulation of a diode circuit
A circuit contains a pn diode (Is = 10-10 A, n = 1.2) and a Thevenin equivelant circuit consisting of a DC voltage source and a 1kW resistor as shown below.
(a) Find the operating point for the circuit using SPICE if Vin = 5 V.
(b) Use SPICE to plot the voltage across the diode as a function of time if Vin rises from 0 V at time = 0 and 5 V at time = 100 nsec. (see note below)
(c) Estimate the turn on voltage, Vf, of the device from the plot. (note, the current is almost a linear function of the input voltage ramp once the diode turns on, so the V vs. Time plot is comparable to the V vs. I plot we have seen in class.
Notes on doing this assignment with B2Spice.
-Start B2Spice Workshop and build the circuit by placing devices, moving them around, and connecting them with wires.
-Set properties for all elements including DC voltage of the source, resistance of resistor, and model parameters for the diode.
-For part (a), set up the simulation by selecting .OP (operating point). Then run the simulation to find the operating point.
-For part (b), change the simulation setup to .TRAN (transient analysis). Set .TRAN parameters tstart, tstop, tstep to 0, 100n, and 1n. To do this select the parameter, enter a new value in the ‘Value’ window and then select ‘Accept’ before moving to the next parameter
-Setup the voltage source as a ramp by double-clicking the source and selecting ‘Piece-wise Linear’. Then click on the ‘Transient Properties’ tab and enter the values as
time1 value1
time2 value2
You can enter the values in the ‘Value’ window or select ‘Edit Table’. Either way, be sure to click on the ‘Accept’ button after you have entered your values or it won’t be saved. Then click ‘OK’ to exit the voltage source properties window.
-Run the simulation. Select the transient plot (called Circuit1-Transient-1.1, or something similar). Right-click on the window and select ‘Edit Plot’. Select the voltage you wish to plot from the ‘Plot list’. Then click ‘OK’ and the voltage will be plotted for you.
-You can plot both the input and the diode voltage if you want, but the plot you turn in should only show the diode voltage. If you’re not sure which one is the diode voltage, select the circuit schematic window, then from the top window select ‘View’ / ‘Show Node Numbers’. The diode voltage will be the voltage of the node between the resistor and the diode (referenced to ground in this circuit).
Professor Mason's: HOME | RESEARCH | AMSaC LAB | EE COURSES
University of Kentucky | UK College of Engineering | UK Electrical Engineering | UK EE Faculty
