Performance-Based Assessments for Semiconductor Circuit Competencies

Use a variable-voltage, regulated power supply to supply any amount of DC voltage below 30 volts. Specify standard resistor values, all between 1 kΩ and 100 kΩ (1k5, 2k2, 2k7, 3k3, 4k7, 5k1, 6k8, 10k, 22k, 33k, 39k 47k, 68k, etc.).

This circuit produces nice, sharp-edged square wave signals at the transistor collector terminals when resistors R₁ and R₄ are substantially smaller than resistors R₂ and R₃. This way, R₂ and R₃ dominate the capacitors’ charging times, making calculation of duty cycle much more accurate. Component values I’ve used with success are 470 Ω for R₁ and R₂, 270 kΩ for R₂ and R₃, 4.7 μF for C₁ and C₂, and 6 to 14 volts for V_CC. The frequency of this circuit does vary with supply voltage, so don’t expect perfect agreement between predicted and measured values.

By the way, this circuit works very well for holiday flashing lights - decorate your lab room accordingly with student-built light flashers!

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.

Use a variable-voltage, regulated power supply to supply any amount of DC voltage below 30 volts. Specify standard resistor values, all between 1 kΩ and 100 kΩ (1k5, 2k2, 2k7, 3k3, 4k7, 5k1, 6k8, 10k, 22k, 33k, 39k 47k, 68k, etc.).

This circuit produces nice, sharp-edged square wave signals at the transistor collector terminals when resistors R₁ and R₄ are substantially smaller than the combined resistance of resistors R₂ and R₃ and the respective potentiometer section resistances. This way, R_pot, R₂, and R₃ dominate the capacitors’ charging times, making calculation of duty cycle much more accurate. Component values I’ve used with success are 1 kΩ for R₁ and R₂, 10 kΩ for R₂ and R₃, 100 kΩ for R_pot, and 0.001 μF for C₁ and C₂.

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.

Use a variable-voltage, regulated power supply to supply any amount of DC voltage below 30 volts. Specify standard resistor values, all between 1 kΩ and 100 kΩ (1k5, 2k2, 2k7, 3k3, 4k7, 5k1, 6k8, 10k, 22k, 33k, 39k 47k, 68k, etc.).

This circuit produces nice, sharp-edged square wave signals at the transistor collector terminals when resistors R₁ and R₄ are substantially smaller than the combined resistance of resistors R₂ and R₃ and the respective potentiometer section resistances. This way, R_pot, R₂, and R₃ dominate the capacitors’ charging times, making calculation of duty cycle much more accurate. Component values I’ve used with success are 1 kΩ for R₁ and R₂, 10 kΩ for R₂ and R₃, 100 kΩ for R_pot, and 0.001 μF for C₁ and C₂.

An extension of this exercise is to incorporate troubleshooting questions. Whether using this exercise as a performance assessment or simply as a concept-building lab, you might want to follow up your students’ results by asking them to predict the consequences of certain circuit faults.