I made a buck converter, And I tested the circuit under following conditions:
Vi = 32V
R = 6.8 ohm
Fs = 125kHz
I got this result:
I think it's kinda odd that the difference between the theoric output voltage and the experimental one get smaller when the duty cycle increases.
The bigger difference between experimental and theoric voltage happens when the duty cycle is close to 0.5, I think two factors may explain this result:
1) The current ripple has its peak just at a duty cycle of 0.5, bigger currents imply a bigger lost since the Ron of the MOSFET.
2) The second one will be that for a duty cycle under 0.5 most of the time the diode is ON, for a duty cycle bigger than 0.5 the transistor is ON most of the time. Since the power loss in a diode is bigger in the diode this may explain the improvement in the efficiency for a bigger duty cycle