Question

A step down converter is used to charge a set of batteries at 12V and a constant power flow of 12W. The input voltage is 40V. The converter is operating at a 300 kHz switching frequency. L is designed to be 56uH while C is designed to be 2uF.

1) Construct an average model, show the schematic of your average model with the same circuit parameters.

2) (Also set inductor initial current to 0 and capacitor initial voltage to 0). Plot inductor current waveform of the switching circuit (1) and the average model on top of each other in the same graph. Plot output voltage waveform of the switching circuit (1 ) and the average model on top of each other in the same graph. Comment the results.

3) Apply an additional output current load step at 0.3ms, with the load step from 0A to 0.25A and pulse width 0.2us. Plot the two inductor current waveforms on top of each other in the same graph. Do the same for output voltage waveform. Both graphs should be from 0.25ms to 0.5ms. Comment the results and specify the time required to reach the new steady state.

4) Apply an additional input voltage load step at 0.6ms, with the input voltage step from 0V to 5V and pulse width 0.2us. Plot the two inductor current waveforms on top of each other in the same graph. Do the same for output voltage waveform. Both graphs should be from 0.55ms to 0.8ms. Comment the results and specify the time required to reach the new steady state.