EE 461G Introduction to Electronics

Homework # 6 Due October 19, 1999

In Sedra and Smith browse sections 4.1 - 4.3, read sections 4.4 - 4.7. Browse section 5.1, read sections 5.2 and 5.3

In Sedra and Smith do problems 4.20, 430 and 4.33 at the end of chapter 4.

In Sedra and Smith do problems 5.8, and 5.10 at the end of chapter 5.

Problem 1

Rb = 100kW, Vac = 15 Vpeak 60 Hz, Vbb = 5.0V, bf = 90

The above circuit is a simple curve tracer from which you can see the BJT's characteristic curve for single value of base current. You may use the spice default parameters for the rectifier diodes and the default spice parameters for the BJT except for the forward current gain bf.

  1. Choose Vbb so that the collector current is 1mA. What is the base current?
  2. Recall that B2 spice requires the x axis data to be monotonic. Choose tend and tstep to plot one characteristic curve of the diode.
  3. For Rc = 1kW what is the maximum Vce you can achieve (with the specified Vac)? Verify the value with spice by plotting ic versus Vce. Also plot Vbe versus time. How does it change with time?
  4. Compute Rc so that the maximum value of Vce is 14V with the specified Vac. Verify the value with spice by plotting ic versus Vce with this new value of Rc.
  5. Change BJT parameter Is in the BJT model to 0.1pA (0.1 10-12A). Run the simulation and determine the new Vbe. Note any changes compared to what you computed previously.