3  Check List

This is the guide for your submission for the lab. The questions are repeated elsewhere though the lab document and collected here for your convenience.

Put all the answers, plots, and oscilloscope screenshots in a single PDF document and upload to Gradescope.

3.1 Tasks

3.1.1 Converter Efficiency

  1. Measure the efficiency of the flyback converter over a load range of \(0.25~A\) - \(1.5~A\) in \(0.25~A\) increments and input voltages of \(12~V\), \(24~V\) and \(32~V\).
  2. Create a plot overlaying the efficiency curves over load current for the three input voltages.
  3. (Post Lab) List 3 components where power is dissipated in the flyback converter, provide the component reference designators of those components from the schematic.

3.1.2 Snubber Design

  1. With \(C_{snub}\) (C11) and \(R_{snub}\) (R21) not installed measure the frequency of the ringing on \(V_{DS}\) during turn-off, \(f_1\). Save an oscilloscope screenshot for your lab submission.
  2. Solder in a \(100~pF\) capacitor for \(C_{snub}\) and a zero ohm resistor or small wire for \(R_{snub}\). Measure the frequency during turn off, \(f_2\).
  3. Given the measured frequencies, \(f_1\) and \(f_2\), and the known additional capacitance in parallel with \(C_{DS}\) when measuring \(f_2\), calculate the values of \(L_{leak}\) and \(C_{DS}\).
  4. Choose \(C_{snub}\) to be three to five times greater than the value you calculated for \(C_{DS}\), subject to the values available in the SMD capacitor kit. This is satisfactory to assume \(C_{snub} \gg C_{DS}\). Calculate \(R_{snub}\) such that \(\zeta = 1.0\) and choose the closest value of resistor available in the SMD capacitor kit.
  5. Solder in the new components for \(C_{snub}\) and \(R_{snub}\). Measure and save an oscilloscope screenshot of the new turn-off transition for your lab submission.

3.1.3 Switching Loss

  1. Provide oscilloscope screenshots of the turn-on and turn-off switching transitions.
  2. Calculate the turn-on and turn-off switching loss. Your answer should be in units of Joules.
  3. (Post Lab) The flyback converter switches at approximately \(250~kHz\). Calculate the time averaged switching loss in watts. Using your results from measuring the converter efficiency, what percentage of the total power loss is switching loss?
  4. (Post Lab) As the MOSFET switches faster switching loss is reduced. The MOSFET gate is modeled as a capacitor and as the resistance of the source driving the MOSFET gate is reduced the MOSFET will switch faster. What is the reference designator of the resistor in the schematic which could be reduced in value to reduce switching loss?

3.1.4 Feedback

Please provide feedback to help make future labs better! Anonymous feedback can be provided via this google form. Feedback is strongly appreciated but feel free to skip answering any of these questions.

  1. Approximately how many hours did this lab take?
  2. Is there anything that you think should be removed from the lab? If so, what?
  3. Is there anything that you wish the lab included or elaborated more on? If so, what?
  4. What is the most useful thing that you learned from this lab?