Topology choice for wide-output-voltage-range SMPS
If your only control of the energy-transfer is by the duty cycle of a switch, then 1% to 99% may be in conflict.

The circuit need two periods:

1) storing energy into the inductor

2) removing energy from the inductor

Storing energy with 200 or 300 volts across the inductor: OK its fast

Removing energy with only ONE VOLT across the inductor (or a schottky diode voltage_drop + ONE VOLT): not so fast.